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John Wiltrout's Blog

116 posts
jw0752

My Muse is Gone

Posted by jw0752     Top Member Sep 13, 2017

For those of you who have known me and followed me over these last 4 years there has been one continuing theme. My Mom with deteriorating symptoms of Parkinson's Disease and me with furtive attempts to use electronics and technology to ameliorate her situation. In addition to countless little twists and hacks to everyday items, we had modified her chair so that it wouldn't over extend, built a pain creme dispenser, designed a power straw to let her drink when she was too weak to draw water up a straw, she had the only remote assistance call button in the home attached to her wheel chair, her call light was modified so it was visible to her in bed, and just as many attempts that were failures. She kept me thinking and inspired. She was also engaged with the electronics and always wanted me to bring and explain my latest projects. We often looked at the E14 forum and she came to know my many friends here.

 

Last week her condition had finally worsened so that she was not able to eat or drink without choking. So many things had been taken from her by the disease that she finally just gave up. Monday night I stayed with her as she was having great difficulty breathing. In the morning I stepped away and returned home and before I could return she was gone. My beautiful, precious, muse was gone and all I could see was the image from just a few days earlier of her sitting in the wheel chair looking at me with her bright blue eyes, her smile still visible through the face robbed of the ability to emote, and trying feebly to wave goodbye to me for the day.

 

I am sorry to throw my sadness in front of you. I may be quiet for a while.

 

John

jw0752

Disaster Averted

Posted by jw0752     Top Member Aug 31, 2017

About a year ago I installed a Water Mains Shut Off system in my home. I blogged about it at the time and here is a link to the final Blog Post where I included a video:

 

https://www.element14.com/community/people/jw0752/blog/2016/07/12/automatic-water-shut-off-system-for-home-chapter-5-final-demo

 

Over the course of the year I have had two times where the system shut off due to a splash of water in the laundry room getting to the sensor. Both of these times the alarm and shut off was trivial since there wasn't really a leak and we were right there when it happened.

 

Today we were finally thankful for the shut off system. The other day my wife brought home a couple of throw rugs that a friend had given her. Since they were originally expensive she decided to hand wash them in the laundry tub. She began by putting them in the tub with some Woolite and turned on the water. Since the tub was taking a while to fill she decided to check on something in the kitchen and, as this scenario usually goes, she got busy and forgot about the running water.

 

I was in my office when she suddenly came running to say that there was a flood in the laundry room and my alarm was sounding in the basement.

 

IMG_1633.JPG

 

This was the scene of the potential disaster. When I took this picture the laundry sink had already been drained and the wet dry vacuum had been used but you can still see the sensor on the floor under the washing machine hookup. After I vacuumed up the spilled water I was please to find there was only about 2 liters that actually made it to the floor before the sensor tripped the main water shut off in the house. If you want to see how the shut off itself works you can use the link above to go back and watch my final demo video.

 

When we finished the project a year ago there was some question in all of our minds if my homemade sensors would stand up or if they would pull moisture from the air and give false triggers. So far there has been no sign of this happening. All three triggers have been for cause and the one today would have resulted in the dumping of considerable water on the floor had the sensor not shut down the main water valve so quickly.

 

John

jw0752

I Love Wire

Posted by jw0752     Top Member Aug 17, 2017

Yes I admit it, I confess, I Love Wire!

 

IMG_1585.JPG

 

A while back Alpha Wire announced the release of a new wire called Thermo Thin Hook-up Wire. Here is their announcement on e14 in case you missed it.

 

https://www.element14.com/community/groups/alphawire/blog/2017/06/08/alpha-wire-releases-all-new-600v-thermothin-hook-up-wire

 

The announcement offered a free sample so I signed up. That was June 8th. Today two months later I received 2 FEDEX packages each containing 2 feet of Red Thermo Thin Hook-up Wire. Since I had forgotten about my request it was a really nice surprise. Did I mention that I love wire.

 

IMG_1578.JPG

 

This is 22 gauge Thermo Thin wire and it has 19 strands of 34 gauge wire covered by an ECA flouropolymer insulation that is rated at 600 volts. The insulation is quite flexible and can deal with a temperature range of minus 150 degrees C all the way to +300 degrees C. The excellent qualities of the insulation keep the external diameter of the 22 gauge wire to approximately 1 mm. One of the first things that caught my eye was how tightly the strands were wound. As close as I could figure it out we see a 360 degree twist for every cm. This gives the wire a lot of extra flexibility as the single strands are slightly helical and can flex without being stretched beyond their ability to recover or suffer damage. I have no test equipment capable of testing the claims of the manufacturer but I see no reason to doubt them.

Here is a link to Thermo Thin wire on Newark Electronics:

 

http://www.newark.com/alpha-wire/2922-bk005/hook-up-wire-22awg-black-30-5m/dp/22AC3402

 

I really wish I had a good application for this wire at this time. I can see that it would be a pleasure to work with compared to the stiff Teflon covered wire we used to use on sterilizers and other heat intensive equipment in the dental equipment field.

 

While we are on one of my favorite subjects I want to continue to talk about some of the wire technologies that have a special place in my heart.

 

The next one is the wire that was used in the coil cords of corded telephones. For those of us who spent most of our lives using corded phones it has to be a surprise that with all the use and all the abuse the coiled cords almost never failed. They could be stretched, pulled, swung and pulled between ones toes while simultaneously scratching the back of ones neck and continue to function properly for decades. In case you ever wondered why here is the secret.

 

IMG_1583.JPG

 

Each of the 4 wires of the coiled cord had its own 4 separate conductors. Each of these conductors consisted of a nylon string with a flat ribbon of copper conductor wound around it like a coiled spring. If you look at the picture you can see where I have separated the copper ribbon from the inner nylon string on one conductor. Remember how impressed I was with the tight winding of the Thermo Thin with 1 twist per cm, well the phone wire has upwards of 15 coils per cm. In this configuration the wire is very much like a coiled spring and our bending and twisting has little or no effect on the copper conductor at any point. The internal nylon string takes up all the linear force and leaves the ribbon of copper to do its job of conducting electrons. One of the products that I developed for the dental industry used this technology to solve a problem. In the dental clinics there were wall mounted x-ray units to take radiographs of the patient's teeth. Each of these units had a coiled cord with a thumb switch attached so that the operator could step out of the room, away from the x-ray radiation, and push the button to make the exposure. These cords were very prone to failure and were constantly in need of repair or replacement. My re-purposing of telephone technology brought the telephone cord into the dental operatory to be used as the cord on these x-ray exposure switches. These cords are still being sold to dental equipment repair people across the world.

 

http://www.chapmanhuffman.com/index.php?main_page=product_info&cPath=7&products_id=461

 

Another of my favorite wires are the rubberized (silicone) test probe and patch cord wires made by Pomona. These 18 gauge beauties just call out to me and beg me to make them into test leads and patch cords.

 

IMG_1579.JPG

 

They are composed of many small gauge strands (192 strands of 41ga according to the data sheet) that make them flexible and durable. I have lived long enough to know that the rubberized insulation will eventually ( 40 years or so ) harden and crumble but no one would be disappointed in this kind of a life span and perhaps the new silicone version will last even longer. In case you would like to make some nice cords for your own lab here is the link to the wire on e14 Newark Electronics. The Red is denoted by a -2 and the black by a -0.  Just a side feature, (they smell nice too).

 

http://www.newark.com/pomona/6733-2/test-lead-wire-50ft-18awg-copper/dp/63H2515

 

Another of my pet wires is not to be found easily. I call them High Strand wire and I have only been able to get them by salvaging them out of expensive dental equipment cords. They are used in the cords that go between a table top machines and the handpieces used by the dentist. In some case they supply the 2 or 3 watts of power needed to light a small halogen bulb that lights the inside of the patients mouth. These wires can have up to a hundred or more individual strands of fine gauge wire all in a 20 to 24 overall gauge conductor. They are extremely flexible and durable. I like to use then in any application where I need to handle currents of up to an ampere and where the wire will under go a lot of bending and flexing. I would not use these wires for voltages over 30 or 40 volts as I am quite sure that the insulation is not rated for higher voltages. If you want to get a hold of some of this wire check with your local dentists and ask them to save their old handpiece cords for you or if you have a dental equipment repair man in your area he probably has a pile of them in a corner of his shop.

 

IMG_1581.JPG

 

The last wire that I will cover here is the Kynar wire wrap hookup wire. I was reminded of this wire the other day when I read shabaz 's excellent DIY test instrument project:

 

https://www.element14.com/community/community/project14/diytestequipment/blog/2017/07/14/cyclops-1000-an-electronic-eye-for-rotational-speed-measurement

 

If you look carefully at the first picture in his blog of the perf board prototype you can see how he has skillfully used the Kynar wire as hookup wire. It is very small diameter and can be threaded through the perf board holes to provide beauty and strain relief. The insulation on this wire is a cousin of the insulation on the Thermo Thin and as such is quite high voltage and tolerant of heat, cold and chemicals. Here is a picture of a 30 gauge Kynar wire:

 

IMG_1584.JPG

 

Now that I have introduced you to some of my favorite wires I invite you to send me pictures and stories about your own favorite wire technology. When it comes to wires just remember that I am a little like a cat lady and your favorite might end up being part of my collection too.

 

John

 

If you have followed the previous 3 posts about this project you know that we are at the point where the rubber meets the road. I have now put the interface circuits, that were previously on bread boards, on to an Arduino shield board. The shield will make all of the necessary connections to the Arduino. The connections from the interface board to the rest of the circuit are being assembled so that I will be able to easily disconnect and remove the interface board for modification or service if necessary. Here is a picture of the completed interface board:

 

IMG_1548.JPG

 

IMG_1550.JPG

 

I have also improved the schematics for the interfaces and included the hookup wire color that is being used to assist me if I have to troubleshoot the unit in the future.

 

Voltage Interface Board Ver 1.bmp

 

Arduino to Clock Interface.bmp

 

As mentioned before both of these circuits have been installed on the Arduino Shield board.

 

For the power hookup which brings 9 volts to the Arduino I have made up a polarized connector using board headers. The rest of the connections to the peripheral circuit are going to be made with Male-Female bread board wires which I have cut in half to produce a color coded connection (see schematics for colors used). While these wires are really quite small gauge they are more than adequate for this low current application. Half of the cut bread board wire is attached to the interface board and the other half is attached to the appropriate point on the peripheral circuits. I always put the female ends on the wires that may be powered when disconnected so that they can not short to other wires or components. Here are a couple pictures of the unit with and without the interface board installed.

 

IMG_1545.JPG

 

IMG_1547.JPG

 

With projects like this I like to layout the wiring harness so that I can open the unit and have access to the circuits without having to stress the wires or their connections. To do this I make sure that the wires all pass over the same edge so that the cover can be laid back as in this photo:

 

IMG_1561.JPG

 

This point in building a project is always the most nerve wracking for me as I am about to turn the unit on for the first time. Though I have checked every connection there is always a chance that it may not work or worse yet there may be smoke and fire. If that happens it would force me into skipping sleeping tonight so that I can get to the bottom of the problem. Fortunately I have been lucky this time and everything comes on and works as planned. I have made a short video of the first tests that I performed on the unit using my power supply to provide the test voltage which I could decrease until it fell below the target voltage.

 

 

Now that I had a functional unit I decided to test it by putting a AA battery under load and seeing how long it would take for it to drop below 1 volt. The PDT has a set of banana jacks that allow an external electronic load to be attached to the device that is being tested.

 

IMG_1533.JPG

 

I hooked up the external electronic load and set it to 300 mA. The Target voltage on the PDT was set at 1 volt and the AA battery was hooked to the circuit and the Start Button on the PDT was pushed. I walked away and returned several hours later. On return the complete light was on and the time on the PDT was waiting at the push of the TIME button. Sorry I have no photos or videos as I forgot in my excitement.

 

Now I wanted to run some experiments that were more predictable so I found the largest non-super capacitor that I had which happened to be 33,000 uF. My plan was to charge the capacitor to 30 volts and then time it through one time constant. I did not need the external electronic load this time as I would use the inherent 75K ohms input resistance of the PDT created by the voltage divider for the arduino's analog inputs. One time constant below 30 volts would be 11.3 volts. Here is a picture of the setup with the 33,000 uF capacitor.

 

IMG_1552.JPG

 

You can see that when the picture was taken 1 minute and 53 seconds had elapsed and the capacitor was down to 28.15 volts. I ran this experiment 3 times and received the following results;

 

Test 1 Elapsed time  41:05     Calculated capacitance assuming input resistance of 75K  =  32,900 uF

Test 2 Elapsed time  42:42     Calculated capacitance assuming input resistance of 75K  =  34,000 uF

Test 3 Elapsed time  42:00     Calculated capacitance assuming input resistance of 75K  =  33,600 uF

 

I wanted to produce a video to demonstrate this type of test so I chose a 350 uf capacitor and charged it to 16 volts. One time constant below 16 volts is 6.03 volts.  This should take about 30 seconds which is more appropriate for a demo video. Just for back ground on this experiment and video I had to do it 4 times before I got it this bad. What I lack as a moderator I less than make up for as a videographer but here it is:

 

 

When I first felt that I needed a timer like the Process Duration Timer I was testing and comparing batteries from different manufacturers. To test batteries properly they need to be allowed to discharge at reasonable rates. The times involved made personally monitoring the process impossible. I built my first timer at that time but I have always found it clumsy to use and it lacked the range to test batteries over 12 volts. The PDT is my attempt to produce a more accurate unit with a greater range (up to 30 volts in this case). As you have seen it can also be used to time the process of capacitor discharge and with a simple interface it should be able to time any electronic or mechanical process that can be connected to a sensor or a switch. All that one has to do is sense the end of the process and pull the test voltage below the target voltage.

 

Thank you to my friends who have taken the time to read and make suggestions that have helped me make this a more successful project.

 

John

 

 

 

 

 

 

The purpose of the Process Duration Timer (PDT) is to provide a means to set up an experiment and time a process, whether it is the discharging of a battery, the discharging of a capacitor or some other process that one does not want to sit around and watch. The PDT allows the experimenter to set up the experiment and walk away. The PDT watches the voltages and pushes the button on the stop watch the second that the process voltage crosses the target goal.

 

In the last three blogs we have built the power supply, the clock circuit , and the interfaces have been designed and bread boarded. Today we will work with the Arduino.

 

All I need at this point to hook things together and test the PDT idea to see if it will work is a properly programmed Arduino. A couple years ago I built a multiple unit project using the Arduino Duemilanove and since I still have several of these boards, this will be the board that I will try to program. I say try to program as this is the part of this project that I am the least comfortable with.

 

I always begin a programming project with a flow chart that takes me on a step by step path through the logic of what I want to do. As you will see the logic needed for this project is very straight forward and even I should be able to program it.

 

Here is a list of the flow chart:

 

Initialize the Timer so that it resets to 00:00:00

Begin Program Loop

     Begin sub loop

          Read the analog pin for the Test Voltage

          Repeat this process 10 times

          Sum the individual readings

          Exit the sub loop

     Divide summed value of Test Voltage by 10 and Store

     Begin sub loop

          Read the analog pin for the Target Voltage

          Repeat this process 10 times

          Sum the individual readings

          Exit the sub loop

     Divide summed value of Target Voltage by 10 and Store

     Test to see if the Test Voltage is lower than the Target voltage

     If "No" start Main loop again

     If "Yes" do the following:

          Turn on the Clock suspend timing relay

          Begin a Sub loop with no logical exit.

 

I got out my arduino programming books, I booted up the Arduino website and got out my notes from previous efforts to program the Arduino. Because it was a very simple program it wasn't long before I had something put together. I also added the ability to print my analog pin readings to the computer monitor so that during the Proof of Concept test I would be able to watch the numbers that would be used by the Arduino to represent my voltage levels. Here is the program that I came up with:

 

/* Program to Zero a clock and then begin reading the voltage from a Test Voltage and comparing
it to a Target Voltage. If the Target Voltage exceeds the Test Voltage the Pin 12 is pulled 
which stops the clock */


const int CLOCK = 10;        // assign the Clock reset function to Pin 10
const int SUSP = 12;          // assign the Suspend function to Pin 12
const int TEST = 0;          // Assign TEST to Analog 0
const int TARGET = 1;        // Assign TARGET to Analog 1
int valtest = 0;
int valtarg = 0;
int vte = 0;
int vta = 0;                // initialize the variables


void setup()
{
  Serial.begin(9600);
  pinMode(CLOCK,OUTPUT);
  pinMode(SUSP, OUTPUT);
  digitalWrite(SUSP,LOW);
  digitalWrite(CLOCK,LOW);
  delay(2000);
  digitalWrite(CLOCK,HIGH);
}


void loop()
{
  vte = 0;
  for(int x=0; x<10; x++)
  {
    valtest=analogRead(TEST);
    vte=vte+valtest;
  }
  valtest = vte/10;
  
  vta = 0;
  for ( int x=0; x<10; x++)
  {
    valtarg = analogRead(TARGET);
    vta = vta + valtarg;
  }
  valtarg = vta/10 ;
  
  Serial.print("Test Voltage:   ");
  Serial.print(valtest);
  Serial.print("     Target Voltage:   ");
  Serial.println(valtarg);
  delay(2000);
  
  if (valtarg > valtest)
  {
    digitalWrite(SUSP,HIGH);
    while(valtarg = valtarg)
    {
      delay(1000);
    }
  }
}

 

This program works but it probably could use some polish. Ideas and suggestions are welcome. I have only improved my knowledge on this site thanks to the great ideas and suggestions for improvement offered to me by my fellow members.

 

Now that I had a programmed Arduino I used my bread boarded interface circuits to put together a working prototype that I could test to see if the Arduino would accept the voltages and make the correct decisions with respect to controlling the clock. Here is a short video of the proof of concept test.

 

 

 

Now that I have a working prototype the next project will be to build the interfaces onto a shield that will mount to the Arduino and then connect it up to the rest of the systems. In the mean time I have completed the mechanics of mounting the switches, Clock and input jacks to the project enclosure. Here are a few pictures of the progress to date:

 

IMG_1527.JPG

 

IMG_1531.JPG

 

IMG_1533.JPG

 

IMG_1538.JPG

As you may have noticed in the second picture above the strain relief I was using was on the mains cord was not conventional nor adequate. I have since rectified this problem with a more sturdy and conventional anchor.

 

In the next and final Blog the interface shield will be built and wired into the system. The wiring will be completed to the switches and controls and I will make a video of the unit in operation.

 

John

 

https://www.element14.com/community/people/jw0752/blog/2017/08/08/process-duration-timer-final-chapter-assembly-and-testing

     I will begin this blog by showing you how I have mounted the power supply into the project box that will be used for the Process Duration Timer. After a lot of searching in my transformer grave yard I found one that will allow the power supply to deliver 0 to 30 volts for the Target Clock Off Voltage. I have mounted a Recon R78C9.0-1 DC to DC converter to the power supply board. This will supply Vin to the Arduino as well as power the clock and the voltmeters for the Test Voltage and Target Voltage. Here are a couple pictures of the power supply and transformer mounted in the project box:

 

IMG_1521.JPG

The loop of yellow wire will run to the main power switch. I have not yet planned the layout of the instrument and control panel. The Yellow , Blue, and Green twisted line in the lower right goes to the potentiometer that controls the Target Voltage which is supplied by the black common and red wire that exit to the top of the picture. The orange wire is the 9 volt supply.

 

IMG_1522.JPG

 

IMG_1523.JPG

I have fused the primary with a 500 mA Slow Blow fuse and mounted the power cord with a strain relief. The power cord is extreme over kill on gauge as it came off an Iron but it was more flexible than the lesser gauge cords in the box.

 

     Since my last blog on this project I have been working on the interface between the Arduino and the Clock board. I wanted the Arduino to be able to send a High out one port to enable power to the Clock board and also send a High out a second port to put the clock into Suspended Animation. The plan is to have the Arduino turn off the clock once on reset (I will call it START eventually) and then keep the clock powered until the Reset is pushed again. Once the Reset is pushed and the clock is timing the Arduino will busy itself comparing the Test Voltage to the Target Voltage. As soon as the Process that is lowering the Test voltage brings it below the Target Voltage the Arduino will send the High out the second port and suspend the Clock. At this point the Arduino will pause until I come back at a later time to record the elapsed time on the clock and reset the experiment. There is minimal challenge to this interface as it is a very standard circuit for this purpose. I am using (2) 2N7000 N Channel Mosfets to do the heavy lifting. Here is the circuit that I put together and tested.

 

IMG_1516.JPG

And Here is a Schematic:

Arduino to Clock Interface.bmp

For those of you with sharp eyes the bread board doesn't match the schematic. The schematic is the correct configuration, though the bread board works this way it isn't the right way to do it.

 

One thing of interest since last time is that I have solved the problem of where I was going to get the 5 volts to energize the relay that puts the clock into suspended animation. I remembered that while the clock itself has a Vin of 9 volts it was followed in the circuit by a 78L05 voltage regulator. This is a small TO-92 device and I didn't trust it to handle the power requirements of both the clock and the relay so I replaced it with another Recon R78E5.0-0.5 which is a 500 mA version DC to DC converter. Here is a picture of the reverse side of the clock module showing the installation of the DC to DC converter. Not surprisingly the current draw on the 9 volt line dropped considerably as the DC to DC converter is much more efficient than the linear 78L05.

 

IMG_1518.JPG

 

By taking the power for the suspension relay from the clock board I was left with only two control lines running from the Clock Module to the Interface Board. Pulling one to ground will turn on the clock itself and pulling the other one to ground will energize the relay and suspend the clock. I bread boarded the interface circuit and hooked it to the Clock Module. I manually simulated the control output of the Arduino and monitored the current drawn by the clock module.

 

     The next interface that I needed to design was the one between the Test Voltage and the Arduino's analog input (0) and the one between the Target Voltage and the Arduino's analog input (1). Since the Arduino can handle a maximum 5 volts on these inputs and since my target and test voltages may be as high as 30 volts a resistor divider seemed to be indicated. Besides just making it a resistor divider I also wanted to put a little bit of averaging into the voltage delivered to the Analog inputs so that spikes and fluctuations would not cause problems. The last thing I wanted to do was to make an effort to balance the two voltage dividers so that the voltage received by the Arduino wasn't weighted in favor of the Test or Target voltages. I wanted to be able to do this without spending hours trying to match the resistors that I chose for the dividers. Here is the circuit that I designed, bread boarded and tested out.

 

IMG_1520.JPG

And the Schematic to go along with it.

 

Voltage Interface Board.bmp

 

Since I am only a Technician and not an Engineer I have special permission to design empirically. The balancer with the 1 meg trimmer and center leg to ground through another 1 meg resistor was what it took to balance the two sides. No calculations needed. To test this I put the same 30 volts on the Target Vin and the Test Vin. I then put my millivolt meter between "To Analog (0)" and "To Analog (1)". I next adjusted the 1 meg trimmer until I had 0 volts on the meter. This told me that my voltage dividers would deliver the same voltage to analog (0) and (1) if the same voltage was provided at Target Vin and Test Vin.  To provide a little stability to the output voltage I have a 10K resistor supplying a 100 nF capacitor before it is sent to the Analog inputs.

 

     While I didn't include it in this discussion I will also have to have a connection point to tie the Volt Meters into the circuitry. Each volt meter will need a +9 volt feed, a ground and then the voltage sense line will go back to the Target and Test voltages. The present plan is to make an Arduino shield board that will contain the two interfaces as well as the meter connection points.

 

     If anyone can see anything that I have done in these interfaces that has "problem" written on it your input would be appreciated.

 

John

 

https://www.element14.com/community/people/jw0752/blog/2017/08/06/process-duration-timer-part-4-the-brain-and-proof-of-concept

Before I show you the power supply module for this project I thought I would share the basic block diagram of the different modules and how the power and control lines will interconnect.

 

Process Duration Tester Block Diabram Horz.jpg

 

As any of the experienced builders on e14 will tell you the more planning that you do ahead of time the less rebuilding you will have to do down the line. I always like to know generally where I am going with a project. This doesn't keep me from changing my mind or having to readjust my plans due to unavailability of parts or if my imagination gets ahead of the technology I can afford. The general block diagram for the hardware and the Flow Chart for the software are useful tools to keep me focused and on track to the goal of a completed functional device.

 

The main topic of this blog is the Power Supply Module for the Process Duration Tester. As I have done in several of my recent projects I am going to use an inexpensive Chinese linear power supply kit and then modify it to suit my needs. Before I show you what the module looks like here are my perceived power needs for this project:

 

1. General 9 volt 1 Amp output to power the Arduino Vin, The two voltmeters, The Clock Module, and with an additional buck to 5 volts to drive the suspension relay of the clock module.

2. 0 to 30 volt variable output to serve as the Target Voltage for the termination of the timing sequence.

 

The need for the 5 volt drop off the 9 volt line comes as a correction to a mistake that I made in my planning and modification of the clock module. I had originally hoped that the digital output of the Arduino could drive the suspend relay on the clock module. When I got around to actually taking preliminary readings on the actual current draw of the relay I discovered that the 100 mA draw would mean that a driver circuit would be needed between the arduino and the clock suspend relay. The voltage needs to be 5 volts as this is the continuous duty cycle rating of the relay. In order to conserve the power load on the 9 volt DC/DC converter module I will probably just use another 5 volt DC/DC converter down line. Those of you who have seen some of my other projects know that I love the little Recom R78 series of DC to DC converters. Here is a listing for one from Newark.

 

http://www.newark.com/recom-power/r-78e5-0-0-5/dc-dc-converter-2-5w-5v-0-5a-sip/dp/62X9499?ost=R-78E5.0-0.5&scope=partnumberlookahead&exaMfpn=true&searchref=searchlookahead&searchView=table&iscrfnonsku=false&ddkey=http%3Aen-US%2FElement14_US%2Fw%2Fsearch

 

The 9 volt unit I am using is a Recom R78C9.0 -1.0 and can deliver 9 watts of power when supplied by a 10 to 42 volts input. If you look closely in one of the following pictures you will see the R78C9.0 as it usually fits nicelly into the footprint of a standard 78XX series linear regulator. I will probably use an R78E5.0-0.5 to convert the 9 volt supply to a 5 volt source to drive the relay.

 

Here is a picture of the power supply board with some notes around the edge:

 

IMG_1500.JPG

 

The nice thing about these boards is that they are a kit so I have the fun of building them before I use or modify them. The construction of this kit did not go without a glitch however. I am not sure if it is the late hours that I usually work or just the senior moments that seem to be happening more frequently but I got two wires to the voltage control pot, which is remote from the board itself, switched. This over sight tied the output of one of the regulation Op Amps to the control wiper and besides not working correctly caused the Op Amp to heat up under the output short to ground it was suffering when the control was turned all the way down. Fortunately the TL081 is a tough little Op Amp and I caught the problem before I fried anything.

 

I made a few modifications to the power supply board to suit my needs. As I mentioned I installed the 9 volt DC to DC converter in place of the linear regulator that is usually used to drive a cooling fan for the main power output transistor. Here is a closeup of the converter:

 

IMG_1496.JPG

 

When properly supported this board can put out 30 volts at 3 amps. I am going to use it for a target voltage source which will have to power a 150 uA voltage sense line on a cheap Chinese meter and also power the voltage divider which will make its modified output palatable to the Arduino's 5 volt analog inputs. This means that I am lifting a feather with a truck jack. Aesthetically this bothers me a little but it will work and I really can't provide the 9 volt source and a 0 to 30 volt variable source in any better (translate cheaper) way. Another advantage to using this board is that it will afford some degree of regulation so that the target voltage does a minimal amount of wandering around.

 

I have replaced the normal current limiting pot on the board with a small trimmer and set it so that it will limit output to 500 mA. I have left the main heat sink off the output transistor to save space as the low current it will be handling can easily be handled by the device itself.

 

I will be installing a 10 turn pot on the voltage control so that it is easier to choose an accurate target voltage. When I took these pictures I was still testing with the standard 10K pot that comes with the kit.

 

IMG_1494.JPG

 

As an additional aid to anyone who wants to use this same board for some of their own projects I offer this re-drawn schematic on which I have penciled some voltage readings. Since my senior moments often cause things to not work as planned I took the time to analyse the board and record normal operational voltages for use in troubleshooting. Sorry if the hand written voltages are hard to see.

 

PS Board Schematic with Voltages.jpg

 

In case you are looking for the source on this board I get mine from here:

 

https://www.banggood.com/0-30V-2mA-3A-Adjustable-DC-Regulated-Power-Supply-DIY-Kit-p-958308.html?rmmds=myorder

 

I will be back in a few days with some more attempts at progress.

 

John

 

https://www.element14.com/community/people/jw0752/blog/2017/08/03/process-duration-timer-part-3-interfaces

This summer my Grandson Ivan has been coming to spend the day with me twice a week. Ivan is a very serious 10 year old with an interest in electronics. I always try to have a plan in place with experiments and activities. These have gone well with Ivan maintaining focus and interest for sometimes a couple hours at a time. Most of the time it's grandpa that needs a break and not Ivan.

 

Today the topic for our day was learning to use the computer to draw schematics. We began with a simple device, an LED Flashlight. I asked Ivan to tell me the separate components that go into making a flashlight. He told me : Battery, switch, LED, and resistor. I put these names on a piece of paper and then we brought up the schematic drawing program that I like to use. I explained that schematics have a general protocol where higher positive voltages begin at the top and the ground or negative is at the bottom. Also the power supply and input begin on the left side and progress to output of the circuit on the right. After showing him the basics of how the program worked I set him to work drawing the schematic and turned my attention to something else.

 

To my surprise a little later he told me he was done and he had produced a workable schematic of a flashlight. We then took the schematic and I asked him to breadboard the circuit. He has done this before so it was not too difficult a task. Next I told him that the circuit was no longer a flashlight but a room light and we needed to install a three way switch set up. I asked him to revise the schematic and then breadboard the revision. This too he was able to do. By now grandpa was smiling ear to ear as this was showing me that he had really learned and remembered many of the things we had talked about and experimented with in our previous meetings.

 

I proposed that we do something harder so I drew a very crude picture of a latching light activated alarm circuit. I did not draw the symbols but wrote words and made a rough rendition of the wiring. I set him to work producing the schematic and turned my attention elsewhere. Here is the schematic that Ivan drew. Keep in mind that this is only the second schematic he has ever drawn.

 

Ivan's Scematic2.bmp

I now had him breadboard the circuit. He needed a little help in the form of hints to watch polarities and prods to check for all the connections to some of the nodes. Here is the breadboard that he produced. All the placement and wiring logic are his own.

 

IMG_1491.JPG

 

The pin out on the momentary switch was confusing at first but once the architecture was explained he went ahead and used both sides of the poles. As you can see between the anode of the SCR and the LED he did a little creative wandering but the circuit worked and we were both pretty happy. Here is Ivan after completing and testing the light sensor.

 

IMG_1490.JPG

 

Over the years I have been proven to be a very poor teacher. I have lacked the patience. The ability to captivate the interest of my children and grandchildren has always escaped me. After 20 minutes their little eyes are usually glassed over and the visions of toys, video games, or anything else besides what grandpa is talking about floating over their heads. This is why today was a great day. I could see progress and success in what Ivan was able to accomplish today and it felt really good to share this with him.

 

John

This is going to be an update and expansion of range for a test device I built and posted on the forum two years ago.

 

Battle of the Batteries - E*** vs D*** vs Bargain

 

The device that I built for that blog was designed to monitor a battery voltage that was under constant current load from a non-programmable electronic load and compare it to a target voltage that was selected by me. It was my purpose to time how long it took for the battery voltage to decay below the set target voltage. Since this process could take many hours I wanted an automated device that would let me walk away and return the next day to see the final results. For this first device I designed it using a comparator and support components which supplied power to an analog electric clock as long as the battery voltage was above the target voltage and then stopped the clock when the battery voltage finally dropped below the target. While this test adapter worked as planned it had several limitations and inconveniences.

 

I have been thinking for some time to revisit this project and to make the following improvements:

 

1. Use a digital clock timer that can be reset to 00:00:00 without having to manually move the clock hands.

 

2. Improve the accuracy of the timing to +/- 5 seconds.

 

3. Have an integral internal power supply to power the unit and produce the Target Voltage selection. ( The original required the use of an external bench supply to power the unit.)

 

4. Expand the range of Monitored (previously called Battery) Voltage that can be tested from 12 volts to 30 volts.

 

5. Expand the concept of the unit to include super capacitors and other processes where an initial energy source is consumed by a load over time.

 

This has been an idea knocking around in my head for some time but the recent posting of the DIY test equipment on the forum has made me put the idea back on the real bench.

 

This first blog will explain the progress I have made on finding an appropriate digital clock and some of the unusual modifications that I had to make to it. Please look with a critical eye at my solution as I am hoping those of you with more experience will warn me if I am making a mistake with this approach.

 

Here is my present best candidate for digital clock timer for the Process Duration Timer:

 

IMG_1469.JPG

 

This is a $3.63 Chinese clock kit. The first thing that I liked about it was that it starts at 00:00:00 when power is first applied and then it begins to time immediately. As I built the kit I intentionally modified it with a mind to building it into the final enclosure. I left the LED display raised and made sure all the other components sat below the level of the faces of the digits. I left the memory battery off, as the fact that it will reset to 00:00:00 each time it is powered down if a asset for this application.

 

* First real problem is how to conserve the time on the clock when the transition of the monitored voltage from above to below the target voltage occurs. Keep in mind that the experiments that this unit will be timing may take many hours and I will not likely be there to look at the clock when the voltage transitions. It may be many more hours before I actually return and want to check the time. The clock system is built around an Atmel AT89C2051 Micro Processor and I have no access to its program nor do I have the skill to modify it if I did. My solution will have to be external and involve stopping the clock without loosing its current time register. I tried using the input switch on the unit to do this but all that it was programmed to do was reset the hours and minutes.

 

After some experimentation I discovered that if I disabled the oscillator clock to the AT89C2051 it stopped timing. I did this by pulling one side of the crystal to ground. (Question  - Is there any reason why this is not appropriate). When the microprocessor has its clock stopped a side effect of the stop is that I am also left with the current output to the LEDs which is usually a single bright digit on the display. I experimented with leaving the system in this state of suspended animation for 40 minutes and when I opened the grounded leg of the crystal the clock resumed at the exact time that it had when it was suspended.

 

The next step was to add a small 5 volt DPDT relay to the underside of the board. One of my concerns was that the additional capacitance of the relay structure that I was adding, to be able to pull the crystal lead to ground, might cause problems. I placed the relay close to the crystal and ground to minimize any capacitance. By now a good survey of the almost unreadable schematic supplied with the clock kit had given me a way to suppress the display of any digits while the clock is in suspended animation. There are six transistors on the unit that control whether a digit displays or not. These transistors all have a common emitter connect to the power supply. I used the second section of the DPDT relay to switch this power feed off to the transistors. In this way the energizing of the 5 volt relay puts the clock into suspended animation and blanks all the digits at the same time. I also used the other touch contact of this pole to light a red LED that I mounted in the place of the memory battery. After cutting some traces and adding a 470 ohm resistor for the LED the back of the circuit board looked like this.

 

IMG_1485.JPG

 

You can see that I have also added a flyback diode to the relay to minimize a voltage spike when the relay is de-energized. The next step is to test the prototype of the timer to see if it does the things that I want it to do. First of all I want it to start off counting when power is applied at 00:00:00. Secondly I want to be able to put the timer into suspended animation for an indefinite period of time. The suspension will stop the clock pulse of the AT89C2051 and suppress the lighting of the digits in the display. To tell me that the clock is in suspended animation the red LED in the lower right corner should light. Here is a video of the proof of concept test.

 

 

I continue to be concerned about my use of the clock crystal for the AT89C2051 to produce the desired suspended animation. If anyone has any input or experience with this, your insights would be appreciated.

 

My next topics for this series of blogs leading up to building a working Process Duration Timer will concern themselves with a suitable power supply to drive the clock, the Arduino that will provide logic control of the unit, and a source for setting the target voltage. Also the integration of the Arduino and the programming thereof. I will also be including a scaling circuit so that the ADC of the Arduino is allowed to use its resolution to the best advantage regardless whether we are testing a device in the 30 volt area or the 1.5 volt area. We will also have to plan for instrumentation so that we can see the test voltage as well as the target voltage. I am sure that more ideas will come as I begin to build and test the individual components. This is probably the first project that I have decided to blog about as I design it rather than wait for a finished project. You just may get a chance to see me flounder and fail and have to be helped to the finish line.

 

John

 

https://www.element14.com/community/people/jw0752/blog/2017/07/28/process-duration-timer-part-2-power-supply

As I was rummaging through some of my stuff this evening I came across this old General Electric Photo Electric Relay that was given to me 60 years ago.

 

IMG_1387.JPG

 

I wondered if it still worked so I hooked it up. It did not work so I began to trouble shoot it for the problem. As I worked on it I was remembering the man who gave it to me. His name was Wilfred Klatt and he worked in some capacity with the local power supply company. At that time it was called NSP or Northern States Power Co. I do not know what Mr. Klatt's job at the power company was but as a close friend of my parents he became the go to guy when they wanted to check out the safety of one of my inventions, prior to letting me plug them into the wall. Mr. Klatt or Willie as everyone called him never hesitated to try to help me out with my electrical questions. When he would find an interesting piece of equipment that was no longer in service and about to be thrown out he would save it for me. This photo electric relay was one of those things. Those of you who are currently inspiring or mentoring a young person, who has an interest in electronics, should take note. Willie Klatt made a contribution to my interest in electronics and as such I am still grateful to him all these years later. Perhaps the person you are inspiring will remember you 60 years from now too.

 

The unit is built around a tube 117P7GT which has two sections one of which is a half wave rectifier and the other a Beam Power section. The photo sensor is a 930 photo tube which has a metal screen that is susceptible to loosing electrons when struck by light and an electrode to collect those electrons. Just as is the case with our more modern sensors the more light that strikes the screen the lower the resistance in the tube. The 117P7GT drivess a SPDT Relay made by C. P. Clare & Co. of Chicago. The label says that the coil has 5000 Ohms and has 37000 turns. I don't remember seeing any recent relays where they tell you how many windings are involved in the coil. Here is a picture of the unit from above.

 

IMG_1392.JPG

 

By now I had a pretty good idea where the problem with the unit was. I could see that the dual 20 uF capacitor, the silver cylinder, had leaked over the years and was no longer a capacitor. I found a couple of 20 uF 250 volt axials and patched them into the circuit using the terminals of the old capacitor as a terminal strip. You can see how I have placed the new capacitors in the following picture.

 

IMG_1391.JPG

 

Check out the one and five watt carbon resistors as well as the old paper foil .02 uF capacitor. Incidentally this capacitor still tested out OK though quite a bit higher than its nominal rating. Here are a couple more pictures.

 

IMG_1388.JPG

 

IMG_1390.JPG

 

The dial on the front of the unit is not for sensitivity as I initially thought but rather a delay on the release of the relay. The unit is quite sensitive to light as I had to go to near darkness to get it to open the relay and then it would close the relay with only the light of a small flashlight from a couple feet away. I can't think of a safe way to use this unit any longer but I will keep it around as it reminds me of Willie and the help he gave me when my electronics interest was new.

A couple weeks ago I received a really nice Tenma Soldering iron from a friend.  The other night while I was looking through the Banggood Electronics I came across a very inexpensive solder iron that reminded me of the handpiece of my new iron. The one my friend sent was a bench station and this one was a direct plug in with a small dial on the handle. It also came with 6 tips so I decided to take a chance and ordered one of them.

 

They were on sale so my total cost including shipping came to a little over $10.00. I figured that at the very minimum the tips could perhaps be used on the higher quality bench station. Here is the link to the Banggood Iron.

 

https://us.banggood.com/Wholesale-Warehouse-Mustool-MT223-60W-Adjustable-Temperature-Electric-Soldering-Iron-with-5pcs-Solder-Tips-wp-Usa-1077119.html?rmmds=myorder

 

The iron was advertised as being adjustable from 200 C to 450 C. When mine arrived however my tests showed that the tip temperature would go no lower than 350 C. I thought that perhaps I got a defective unit so I wrote to the company. After posting the complaint I realized that for $10.00 nothing was going to come of my inquiry and with so little to loose I decided to crack it open and see what made it tick.

 

The unit came apart very easily. The small knob popped out of a trimmer mounted on the board. The front heater housing unscrewed and the heater and circuit board pulled out to the front. It looked like there was no temperature sensing involved but only a triac dimmer circuit powering the heater. I reverse engineered the circuit and made a schematic.

 

IMG_1249.JPG

The circuit board and heater.

 

Mustool MT223.bmp

 

In the original design the output control trimmer had a 200K Ohm resistor (R1) in parallel. This brought the maximum resistance across the trimmer to about 137K Ohms. 137K Ohms would cause the current through the triac to settle around 150 mA which meant about 18 Watts to the heater element. I removed the 200K resistor and began experimenting with the 500K Ohm trimmer alone. By setting a resistance greater than 137K Ohms and then measuring the stabilized temperature of the tip I was able to determine that what I needed was a minimum resistance across the 500K trimmer of 175K Ohms. This produced a current of 50 mA and about 6 Watts of power to the heater. After an extended warm up period the temperature of the tip would stabilize around 200 C. The formula for parallel resistors said that I would need approximately 300K Ohms for R1. Reality forced me to use a 294K Ohm instead as that is as close I could get with supplies on hand. After reassembly of the iron I again tested it and found that I could now control the temperature from 200 C and up. Caution is needed if the trimmer is turned all the way up. At 60 Watts the little iron quickly streaks past 500 C and the nice iron clad tip turns into a piece of junk. Here is a closeup of the iron reassembled and the control knob which will probably need to be protected with a cover to keep it from being moved by normal handling.

 

IMG_1250.JPG

 

IMG_1251.JPG

 

If you don't mind a little fun modifying it this is a fun project. However, if you want to use it out of the box the high minimum temperatures from the factory will make it short lived and difficult to use. The heater element is a 110 Volt unit as opposed to a 28 Volt one in my bench unit. The spare tips that came with it are compatible with the Tenma Bench unit.

 

John

In the good old days (I remember them well) we didn't use any of the newfangled highfalutin semi conductors to regulate current. When necessary for short term precision current regulation we used a mechanical current regulator like this one:

 

IMG_1234.JPG

 

It is built a little like a high quality buzzer and you can see the precision adjustments for both the tension on the armature and for the position of the contact points.  As the current in the coil increases the contact is opened for a longer period of time. In this way, much like a PWM circuit the current is averaged over the amount of time on and the time off. This current regulator circuit was used to drive the heater filament in an x-ray tube. The mass of the filament allowed it to average the energy from the on and off pulses delivered by the regulator.

 

Incidentally the energy of an x-ray beam produced by an x-ray tube is controlled by the voltage potential between its anode and cathode. The current that is delivered to the filament controls its temperature and therefore the supply of free electrons that are available to be accelerated into the tungsten target. The more electrons that are available the greater the density or brightness of the x-ray radiation. This current regulator was in essence a brightness control for the x-ray beam.  Most x-ray machines are rated based on their kVp and their mA. Modern chair side dental x-ray machines are usually in the range of 70 kVp and 5 mA. Back in the days of this mechanical regulator 90 kVp and 15 mA were more common as the sensitivity of the film wasn't as good and of course there were no digital electronic sensors. The other control that is available for exposing the film or sensor is the amount of time that the beam is applied. As you can imagine the x-rays were applied for a much longer time years ago than they are now. When Grandpa had his x-rays taken back in the 1950s he got several hundred times as much radiation as you do now when you visit the dentist for the same pictures.

 

For the fun of it I hooked this old regulator up to an LED and started to turn up the voltage. At 20 volts the circuit began to regulate at around 15 mA and between 30 and 60 volts the regulation of the mA had about a 10% tolerance around 10 ma.

 

Here are some pictures from my experiment:

 

IMG_1235.JPG

 

IMG_1236.JPG

 

Since the regulator is at its core a small buzzer and it produces a low pitched tone that increases in frequency as the voltage is turned up.

 

John

Thanks to a gift from a good friend I have for the first time in my 60 year walk with electronics a temperature controlled solder station Up until now it has always been one or two unregulated power levels As is the case with most of the things we are accustomed to we are hesitant to try something new Here is a link to the Tenma  21-1011521-10115 solder station from Newark Electronics which I recieved

 

http://www.newark.com/tenma/21-10115/soldering-station-esd-safe-60w/dp/56T2208

 

Here is a picture of the  21-1011521-10115 set up on the bench

 

IMG_1215.JPG

 

The first thing that I noticed about the iron itself was how light it was. My old faithful soldering iron clocked in at 90 grams but the new one was only 50 grams. Besides being 40% lighter it was also 4 cm shorter in over all length. This lighter weight and shorter body will result in less wrist and hand fatigue.

 

The unit is designed with a small ceramic heater that converts 60 Watts of power and is small enough to fit inside a 4 mm diameter cavity in the base of the tip. Since the heater is so integral with the tip the heat up time is extremely fast and the ability to respond to demands for heat from large traces and pads is very good. Warm up from room temperature to operational temperature is roughly 30 seconds. Here is a close-up picture of the handpiece.

 

IMG_1217.JPG

 

IMG_1225.JPG IMG_1226.JPG IMG_1227.JPG IMG_1228.JPG

 

The control itself will display the temperature in degrees Fahrenheit or Celsius. There are three adjustable preset temperatures that are selectable by pushing one of three buttons. The response up or down is very fast due to the relatively low mass of the tip. I have chosen my low temperature of 275 C for light jobs, 310 C for my standard jobs and 400 C for larger mass connections. Since I am still experimenting and getting used to the iron these temps may change in the future. If you adjust the temperature of a setting the display shows your target temperature and then toggles to actual temperature for normal operation. There is even a way to calibrate the temperature. I tested my unit with a thermal couple meter and found it was within 2 degrees C of actual. This is well within acceptable tolerance, particularly in my hobby shop.

 

Here is a closeup of the front control panel which is simple and very functional.

 

IMG_1229.JPG

 

While I only have a week or so experience with the Tenma  21-1011521-10115 I am very pleased with it in all ways and I would recommend it to anyone who wants to upgrade from the challenge of using a non-regulated solder iron.

 

Thanks to my friend who made this possible.

 

John

There are two stations at my main work bench. The first station is for bread boarding and testing components, circuits and prototypes. The bulk of my test equipment is arranged at this end of the bench. The other end of the bench is set up for soldering and desoldering as well as minor mechanical operations. After setting up this arrangement I found myself frequently jumping back and forth from one end to the other to test this or that component as I removed them from salvage circuit boards. Finally I got tired of the slide back and forth and I added a couple of meters to the solder station end of the bench. This solved the problem of having to move to do the minor testing. Here is a picture of the two meters at the solder station end of the bench. I always like to have a small analog meter handy as I find it much more intuitive for checking transistors and diodes. Of course the digital meter is a real necessity when it comes to resistance or capacitance readings.

 

IMG_1219.JPG

 

Yesterday I was busy testing capacitors when I noticed that I was having trouble seeing the smaller print on the read out of the digital meter. Was it a uF, an nF, or a mF in the small units indication? I reached up and pushed the back light timer on the meter and went back to make my test again but before I could get the probes positioned the back light would time out. This happened twice before I gave up. Now I know I can adjust the time that the back light will stay lit but I don't like using the back light as it eats up battery time. The solution would be the installation of a small LED under the counter light. I remembered that a while back I bought some inexpensive automotive bulbs. These are 12 volt 100 mA so you know there isn't going to be very much light but all I needed was enough to highlight the display on the Digital meter.

 

IMG_1224.JPG

 

I checked in the parts grave yard and found a medical equipment wall wart the bragged 12 volts 2.5 A. I always get a kick out of situations where some of this once expensive, elite dental equipment gets tied into running something like a fifty cent Chinese LED. My bench lights can be controlled so that I do not have to have them all on at one time. I light, with spots,  which ever end of the bench I am working at and leave the other end with just the ambient room light. Fortunately I had a spare switched outlet for the solder station end of the bench so that is where I plugged in the 12 volt wall wart. I had to extend the wire of the wall wart about a 30 cm to reach the proper position. Here is a picture of the wall wart plugged into the switched outlet.

 

 

IMG_1221.JPG

 

Here is the LED positioned behind the shelf edge above the digital meter.

 

IMG_1222.JPG

 

Here are the before and after pictures of what I can see from my working position at the solder station.

 

IMG_1219.JPG

 

IMG_1220.JPG

 

This is a very small and simple project but it will lower my frustration level and it will make working at the bench much more enjoyable. Perhaps there are little irritations that you are dealing with everyday as you work at your bench. No time like the present to get out the tools and make that simple modification that will put more enjoyment into your experience. Then post a blog like this one so we can all enjoy your triumph over life's little irritations.

 

John

It has been a while since I did the last Shop Tip Blog. These are blogs about some of the simple things I have discovered that make working in my shop a little easier. Today I realized that I had not mentioned how useful a Lint Roller can be.

 

When I have finished a build or a salvage operation on a piece of electronic equipment there is always a mess of debris, metal chips, wire snips, and solder splatter left over. To me, it is very important that none of this debris gets to the floor. The floor is cheap laminate wood and if the small bits of metal get picked up by the casters on my chair they act like little grinders and will eventually wreck my floor.

 

I begin my clean up by picking up the larger pieces or whisking them into the garbage. The solder splatter is scraped off the glass plate that I usually work on and saved for recycling. This leaves the glass plate and bench relatively clean but there are always smaller pieces that are left over. This is where the Shop Tip comes in.

 

This is an inexpensive lint roller that is intended to clean lint from clothing. I get them for $1 at the dollar store.

 

IMG_1190.JPG

 

It is a roll of very thin sheets that have a tacky surface. When the sheet becomes saturated with debris it can be pealed off to expose a new surface. I use the roller to clean the surface of the work bench as a final touch to pickup the debris that is missed by the whisking and scraping. This has kept my floor free of caster damage.

 

Here is what the roller looks like after a typical use.

 

IMG_1189.JPG

 

John