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John Wiltrout's Blog

107 posts
jw0752

Thank You Wilfred Klatt

Posted by jw0752 Top Member Jul 10, 2017

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.

 

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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.

 

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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.

 

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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.

 

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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.

 

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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.

 

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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

jw0752

Mechanical Current Regulator

Posted by jw0752 Top Member Jun 16, 2017

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:

 

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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:

 

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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

 

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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.

 

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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.

 

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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.

 

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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.

 

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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.

 

 

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

 

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

 

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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.

 

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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.

 

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John

jw0752

It's Not Just the ESD (Static)

Posted by jw0752 Top Member May 18, 2017

I had a very challenging time last night. I have been working on producing a decent prototype of a machine I described in a previous blog.

 

https://www.element14.com/community/people/jw0752/blog/2017/04/17/prototyping-an-emdr-machine

 

The construction had been proceeding very well until last night as I neared completion and initial testing.

 

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To power the LED Scanner I had decided to use the 2N7000 400mA  logic level MOSFETs. These, eleven in all,  had all been soldered into the board. and all the necessary connections had been made to the reverse side of the board. It was all neat and pretty except for one thing. It didn't work properly. It looked like most of the MOSFETs were showing a partial short from D to S.

 

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A quick check with the meter showed that this was the case. 10 of the 11 MOSFET had from 10 to several K ohms of short between their drains and sources. My initial thought was that I had been careless with handling them and that static had gotten them. I hated what I had to do but I began to peal back the wiring from their contacts and with all the care and grounding straps I could find I replaced them one by one. At last reassembled I once again applied power and voila! Same problem, same appearance of partially shorted MOSFETS. So we dove back in for another go at it. This time I monitored the status of the MOSFETS as I went along. To my surprise they were being killed by me as they were being installed. At this point there was no way that static was to blame. Too many precautions and ground wires. It dawned on me at this point I was perhaps heat damaging them as I soldered them in. Because of space considerations the MOSFETs had been pulled down fairly tight to the board leaving about 3 mm of lead before entering the board. My solder iron does not have temperature control and runs at about 325 C. The data sheet for the 2N7000 says that it can tolerate 300 C on a 1/16 inch lead for 10 seconds. I think, from my experience, this is a bit optimistic. My usual technique is to minimize time on the contact but obviously something was damaging these parts. I got out the heat sink clips for leads and carefully began to replaced the remaining bad FETs. I continued to monitor them as I installed them. Since I was tacking wires and resistors to their solder pads It was necessary to make extra certain that time on the pad was minimized. I also sprayed coolant on the heat sink clips. Despite these precautions I still managed to kill a couple more. Finally after 6 hours and lots of frustration I had the machine up and running properly.

 

In all I killed 19 of the 2N7000 MOSFETS

 

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Fortunately for the pocket book they are not expensive and while I did not have any left to spare after this debacle I did have exactly enough to complete the job.

Here is a picture of the completed project:

 

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Here is a short video showing how the lights scan back and forth while hand held tactile devices buzz periodically in the patient's hands and a tone is emitted in the patient's ear as the light on the bar hits each end. I personally question the therapeutic value of this device but then what do I know, I am a technician who can't even seem to install eleven MOSFETs without Killing 19 of them.

 

 

John

Despite 60 years of playing with electronics this is the first time I have seen a DC motor wired in this fashion.  At first I did not expect it to work on DC current but to my surprise it took off and ran perfectly. Furthermore it did not matter if the polarity was forward or reversed. The motor continued to spin happily along. Just for the fun I also applied an AC current and once again the motor continued to whirl away. Here are some pictures of the motor wiring:

 

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Just to clarify how the motor is wired I also produced this small schematic:

 

Novel DC Motor Wiring.bmp

 

On first appearances I assumed the motor would start to turn and then stop when the small tantalum capacitor became charged. I did not initially understand why this did not happen. I am hoping some of my friends on the Forum with more experience and knowledge will confirm my speculation that the counter EMF in the motor actually discharges the capacitor allowing it to accept a second charge and continue to maintain the magnetic fields that spin the motor. I suspect that the low ESR of the Tantalum caps makes their charge and discharge rapid enough to facilitate this process. I do not know why the designer of the piece of equipment where this small cooling fan was used chose to use this particular circuit. It was something new to me and it caught my attention. Now I just want to understand it.

 

John

If you are looking for an inexpensive kit build project that comes together nicely and works well to boot check out the DSO Shell 15001K Oscilloscope Kit.

 

https://www.banggood.com/Orignal-JYE-Tech-DS0150-15001K-DSO-SHELL-DIY-Digital-Oscilloscope-Kit-With-Housing-p-1093865.html?rmmds=myorder

 

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At $22.00 including shipping from China this is a no brainer. With a 200K bandwidth (Perhaps a bit of an exaggeration) it is undersized for many applications but still is a good tool for Audio and lower frequency servicing as well as a good educational tool for the experimenter or enthusiast. This model of the unit comes with all the SMD components installed. The through the hole components, switches and connectors are left for the kit builder. Here is what comes in the package:

 

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Note that while you see a probe in some of my pictures this is not included in the kit, nor is the 9 volt power supply. I found that the small wall warts that I use for the Arduinos worked well. I also put a battery pack on the back of one unit so that I have a portable model. The manufacturer cautions that 10 volts is the high limit of the power supply and damage may result if the unit is powered with a higher voltage.

 

Here are what the circuit boards look like out of the box:

 

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The kit comes with 4 pages of assembly instructions, calibration, and operation manual. While it is over all adequate it takes a lot of looking close and a thorough reading to get it right the first time. I have build three so far and I still can't quite get it right. It is not that the correct procedures aren't explained or illustrated somewhere on the pages it is just that it is not a totally smooth sail and I have a tendency to use my intuition too much. Fortunately a couple redos are permitted. The solder points are very small and a little challenging so this may not be a kit for a first time builder. Better to have some soldering experience first though it is doable if someone with experience is supervising a beginner.

 

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The resistors supplied are very small and 5 banded. My 68 year old eyes had a challenge with them so I just metered them and put them where they belonged. If you happen to have some of my special tungsten carbide meter probe tips you can check 1/8 watt resistors one handed like this:

 

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When the main board is fully populated they have you plug it in to check for proper operation. The instructions are a little out of sequence so it is necessary to populate the board and then go back to the first instruction on the list telling you to test it. At this point all one can do it see the screen and toggle the function buttons.

 

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I found that the vias did not pull the solder in quite as easily as I would have liked so a good inspection of both sides of the board after soldering allowed me to dress up a couple questionable looking joints. The Analog board is the board where the bulk of the through the hole components must be installed. Over all the instructions were good and the components easy to identify. On the first two units that I built I mounted the adjust control backwards on its board. This does not harm anything but the unit will not work properly. If the instructions are read carefully they have a small box with a red print warning not to do it the way I did. Once this error was corrected both of the first two units worked properly. Here is the small board showing the side not to mount the control on.

 

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The analog board comes with two sets of header pins so that during calibration the main board can be off set to allow access to the adjustments. While in this position one can check voltages and tune the input to display a clean square wave.

 

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One feature that I was really pleased with is the ability to toggle on and off a list of measurements. Usually on a meter this size and cost one is left to guess what the digital data is. Here is what the unit looks like with the measurements displayed:

 

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I put a battery pack on the back of one unit to make it more portable and purchased a set of $10.00  Oscilloscope probes for the units. The probes like the oscilloscopes came with free shipping but this time the Chinese had them shipped to me from the Seychelles. The ways of the electronics world are hard to believe. I am enjoying this era of free trade and exchange of products. I wonder how long before the politicians see what is going on and screw everything up. Any how if you like to build things this was a fun little project with very little financial risk involved. Here is a picture of the back of my unit with the battery pack and a picture of a completed unit.

 

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Have Fun.

 

John

jw0752

Zener & LED Tester

Posted by jw0752 Top Member Apr 23, 2017

While sorting out and reorganizing my collection of mostly salvaged zeners the other day I began to imagine what I would have to do to make a simple tester. In the past I have set up the power supply, milliammeter, voltmeter, and a variety of current limiting resistors to test the questionable zeners. After considering the problem for a while I decided that a custom power supply with a few modifications would make a perfect zener tester. I also realized that it would also do double duty as an LED tester.

 

Here are the parameters of the modified power supply that I envisioned.

 

Variable voltage control from zero to thirty volts.

 

Variable current limit from zero to 1000 mA.

 

Digital display of output current in mA and voltage across the device under test.

 

A means to calibrate a target mA limit prior to connecting the part to be tested.

 

A way to connect the component to be tested easily.

 

 

A quick inventory of my parts graveyard revealed that all the necessary components for this build were already at hand. I would use the same Chinese power supply kit that I had been using in my recent bench power supply builds.

 

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This board which is available from a Chinese Source for $10 accepts an AC input of 24 Volts and will control 0 to 30 volts output at a max 3 Amps. It also has a current limit control so that one can turn the voltage up all the way and it will self regulate the voltage to produce a constant current output. This constant current control was exactly what I needed to make the zener tester work. Since the applications that I will be testing will require currents in the low mA range I began by seeing if I could make the board work well in this range. The unit comes with a 10K potentiometer that with a 270 degree turn moves the current limit from 0 to 3 amps. For this project my preference would be a ten turn pot that controls the current between 0 and 1000 mA. After some experimentation I found that by substituting the following circuit in place of the original 10 K pot I got the result I wanted.

 

Current Pot Modification.jpg

 

The next problem that I would have to overcome was the display of the digital meter that I hoped to use. I have used these meters on my power supply builds and they will display 0 to 100 volts to a resolution of one tenth of a volt. This will be satisfactory for my needs but the current section with a built in shunt that displays 0 to 10.0 Amps will not have the resolution that I need. I began modification of the meter by removing the factory current shunt and the installation of some low ohm resistors. After several failures I finally got close with (2) 0.1 ohm resistors in parallel. I was then able to fine tune them by adding extra solder to the leads to slightly lower their resistance further. The end result was not off as much as the linearity of the meter over the 0 to 1000 mA range so I was satisfied. The beauty of making test gear for oneself is that you can tolerate the accompanying imperfections with more grace. Here are pictures of the meter front and back.

 

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I decided to put a switch on the output that would allow me to switch the control board's output between a dummy load that I could use to precalibrate the target mA and the actual output to the test leads. By having a center off for the switch I have the added benefit of a parking position between tests. This idea of the switch was given to me a couple years ago by mcb1 in one of the many inspirations he has contributed to my devices over the years.

 

By now I had collected the case, transformer, control board, meter, and other parts I would need.

 

I tested the transformer that was a perfect fit for the enclosure and I was dismayed that it put out 30 VAC instead of the 24 VAC required by the board. I have had enough experience with the board to know that this voltage level would stress and probably damage the circuit. In a normal build I would have gone in search of a different transformer but two things made me reconsider. Number one, it was a perfect physical fit which is not always the easy part. Secondly, this application had a relatively low power requirement. I decided to try an old trick where loss of overall power isn't a problem and went in search of a small transformer or inductor that I could put in series with the main transformer. Just as we can use a resistor divider to adjust voltages I would make an inductive divider to lower the voltage to the primary of the transformer. With some luck I found the secondary of a small transformer that moved the primary voltage of my main transformer to 96 VAC and the secondary voltage to a very acceptable 24.4 VAC. In the pictures that follow you can look for the small blue transformer serving as an inductive voltage drop for the main transformer. I did not check it but I was probably inducing a hundred volts or more on its primary. I cut the leads off flush and sealed them with epoxy so they would not be a factor. I have made a note for an experiment some night to see if I can adjust the voltage output of one transformer by loading the secondary of a second transformer that is in series with it.

 

Here are some pictures of the build sequence. You may notice that I do not try to give instructions for building any of my projects. This is because my builds all come from my own pile of junk parts and most would not be able to be duplicated by a second builder. Even I am not usually able to duplicate a build. The idea of the build is however always offered to anyone interested and I will always answer questions below as to how you can integrate your own pile of parts to do something similar.

 

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The case came from an old dental cure light. I have used these cases in the past for single channel bench power supplies.

 

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Before wiring has begun

 

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The little blue inverted transformer in the back left area is the inductor that is reducing the voltage of the main transformer primary.

 

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The completed wiring prior to closure of the case.

 

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The finished front panel.

 

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Testing a Blue LED at 16 mA and the meter showing the junction drop of 3.2V.

 

The bright CC Mode light comes on whenever the board is controlling the voltage to maintain the target current.

 

John

 

 

 

 

jw0752

Prototyping an EMDR Machine

Posted by jw0752 Top Member Apr 17, 2017

One of my Grandsons recently was telling me about a type of psychotherapy that is used to treat PTSD and other traumatic incidents called EMDR, Eye Movement Desensitization and Reprocessing. He described a machine that was being used by therapists that consisted of a light bar mounted on a tripod. The row of LEDs on the light bar would move back and forth from end to end. The machine also had hand held vibration devices that are placed in each of the patients hands and a set of headphones. During the therapy, between counseling, the patient is instructed to sit with their head fixed and follow the movement of the LEDs with their eyes. While the LEDs of the left side of the bar are lit the vibration device in the left hand vibrates and while the lights on the right side of the bar are lighting the right vibration device vibrates. As the terminal LED at each end bar lights a tone sounds in the corresponding ear of the headphones.

 

If you have further interest in this Therapy Topic here are a couple links to get you started:

 

http://www.emdr.com/what-is-emdr/

 

http://neurotekcorp.com/

 

My Grandson's question to me at this point was whether it would be possible for us to make one of these light bar machines. Since I like a little purpose to my explorations I decided it would be a good project to explore. I began with a simple scan circuit based on a 4017

 

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This very properly makes the lights scan from left to right but rather than returning it jumps back to a left right scan each time. I decided to extend the counter by one more stage and use the outputs of the second 4017 to reflect back on the LEDs so that the first 4017 would light the string in one direction and the second 4017 would light the lights in the opposite right to left sequence. I also had to be aware that ultimately the left side of the string would have to be distinguished from the right side. The Data Sheet for the 4017 provided the information necessary to add another 4017 to the string. An MC14081 "AND" gate was also necessary for the logic of this addition. The circuit was built and now I had a string of 17 LEDs flashing from left to right. Now I had to find a way to power the LEDs of the first 4017 using the second 4017 in a reverse order.  I began by putting 1N4148 diodes on each of the 4017's outputs. This would allow me to power the LEDs from each 4017 without any interference. I also removed the current limitation resistor(s) on the LEDs and isolated the return leads of the left from the right side LEDs. Instead of current limiting resistors I installed a separate simple one transistor current sink for each side of the nine LED string. My hope was that ultimately I would be able to use an OPAMP to sense when each current sink was being used so that I could turn on the correct vibrator to correspond to the right or left side of the bar. The tone in the headphones could be driven by a MOSFET linked to the end LEDs. A small capacitor and resistor on the drain of the MOSFET would allow me to control the amount of time the MOSFET remained on and hence the duration of the tone. For this prototype I just powered small piezo buzzers (sonalerts) whereas a production unit would have to have oscillators and a small audio amp. To simulate the hand vibration unit I salvaged vibration motors from some old cell phones. The Op Amps that I used to discriminate the left current sink from the right one were a bit sensitive but functioned properly. I believe that a production model with improved inter device connections would improve this problem. A nine volt linear regulator was installed to stabilize the voltage to the unit so that the op amps stayed in calibration.

 

Here is a picture of the finished prototype board:

 

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I am sorry but I have not produced a schematic of the unit and I probably won't. While it is very functional it is unlikely that it has been anything but a learning experience and is not likely to ever be produced in this configuration. As it got more and more complicated it occurred to me that a Micro Processor like an Arduino would easily handle this function with many less components and complexity. I have made a video of this board in operation and I will attach it at the end of the blog.

 

At this point I decided to develop a second prototype based on an Arduino Duemilanove. The program was very simple and linear with very little logic involved. I wanted to control the speed of the scan of the lights so I put in a potentiometer that could be read by an analog input and then the value used as a value in the "delay" command. Once that was done it was simply a matter of telling the arduino to turn on and off LEDs, vibrators, and sonalerts in the proper sequence. The circuit itself was a lot simpler although the use of the jumper wires from the Arduino outputs to the LEDs makes the board look quite cluttered and obstructs the view of the LEDs. While the sonalert beepers could run directly off the outputs of the Arduino the 150 mA at 3 volt draw of the vibration motors was too much current for the outputs. To handle this I used the 9 volt power supply and MOSFETs driven by the outputs of the Arduino to power the vibration motors. To control the current to the motors to the proper level I once again constructed a simple one transistor current sink to ground and fed both motors to it.

 

Here is a picture of the finished prototype board.

 

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Here are videos of the two different prototypes each doing basically the same thing.

 

EMDR Prototype built using discrete components.

 

EMDR Prototype using Arduino Duemilanove.

 

This has been a good experiment as I have had the opportunity to refresh my experience with the 4017, 555, and 14081 IC devices. I have also had some fun playing with simple current sinks that can be used in lieu of current limiting resistors when supply voltage isn't stable or other considerations are important. Further the utility of MOSFETs continues to impress me. I have had the basic skills to use MOSFETs for about three years now and I do not know how I survive the other 65 years without them. This project has also forced me to once again remember that despite my old fashion gravitation to the use of discrete ICs and other components the microprocessor is a better solution in many cases.

 

John

I was busy salvaging a bunch of Dental electronic equipment for interesting parts when I came across this interesting circuit board construction and I thought you might get a kick out of it.

 

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This is a driver circuit from a handheld LED composite cure light. It allows the operator to select a timer setting and drives a high power LED that has it's light output towards the blue end of the spectrum. The unit also controls a cooling fan the size of a dime to help cool the LED. In order to fit the needed components into a body witha diameter on the order of a broom handle they had to stack a set of circuit board disks 2.2 cm in diameter.  Pretty cool!

jw0752

Hacking a Toroidal Transformer

Posted by jw0752 Top Member Mar 15, 2017

I have this beautiful Toroidal Transformer but it is 19 Volts and I need 24 Volts for my application.

 

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It has a nice big donut hole and I have plenty of 16 GA solid enameled wire so I decided to add a few more windings. The first step was to figure how many windings I would need. I used some lighter gauge wire and wound 10 windings, hooked up the transformer and measured the voltage. I had 1.7 volts for the ten windings so 29 windings should give me the boost I need. This can't be too hard, I thought. I made a loose coil of wire and kept winding it around and around until I had the thirty that I needed. Next I secured one end of the wire to one of the existing wires and started to work backwards. I pulled the wire as tight as I could and went around and around until I had worked my way back to the last wind. Here is what it looked like.

 

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Now that looks simple enough but I am writing this blog to let my hands stop aching. That was really hard work. I had to wonder how they wind these transformers when they have to put hundreds of winds on them. I can't imagine what kind of machine would be able to perform what I just did with my hands. If anyone knows how they do it I would really like to know.

 

I next used some cloth tape that I had and began to wrap strips around the transformer to hold the windings in place and to protect the wire. Here is the transformer after this procedure.

 

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Finally I figured out the correct phase so that the voltage in my windings would add to the existing secondary and made a good solder connection. A few more winds of cloth tape to polish things up and I was done. A test of the transformer revealed 25 volts output with 118 Volts input.

 

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Now that my hands are rested I am going to go back and make another one.

 

John

There have been many times when I have wished that I had a hot air heat source that could be controlled. The rework station has a controlled heat source but it will not work below 100 C. For this project I have decided to build a modified hot air gun that will have controlled temperature output between room temperature and 350 C. This should be very useful for testing and calibrating devices using thermistors. I will begin by hacking my inexpensive heat gun from Spark Fun.

 

https://www.sparkfun.com/products/10326

 

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I began by opening the gun and removing the connection of the motor from the heater taps. The common practice in these devices is to put the mains across the heater element and then take a tap off the heater element around the 15 volt level, rectify it and use it to power the fan motor. For this project I wanted the fan to be tied to a fixed 12 volt source and independent from the variable AC voltage I will put on the heater element. Once the motor was cut loose from the heater element taps I removed the diodes from the back of the motor housing and installed a length of high strand flexible wire. Later I would pull a silicone sheath over the heater and motor wires to make the cord from the control to the gun functional. You will see this cord in later pictures.

 

The heart of this project is a small variac, about the size of a soft ball, that I salvaged from an old Ritter Dental X-ray.

 

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Besides the full 0 to 110 volt sweep contact this unit also had hard taps at 8, 17, and 55 volts. My plan is to rectify the 17 volt tap and use it to drive a 7812 regulator which in turn will provide the power for the fan in the gun. My test of the fan motor showed that it drew 0.25 Amps at 12 Volts and ran with enough RPM to serve my purpose. The 7812 can handle 1 amp when heat sunk so with a small radiator it should be able to dissipate the watt or so it will be required to shed.

 

It is not my intention to build a precision device but I do want to have some indication of what my input settings are so I can estimate the output temperature. Therefore an AC voltmeter will be used to monitor the voltage that is powering the heater element. I will combine the voltage with an empirical listing of approximate output temperatures on the dial of the variac to get my output temperature as close as practical to my target temperature. There are many variables that will contribute to the output temperature of the air. I have attempted to limit and control some of the variables such as the fan speed and the voltage to the element but ambient temperature will also be able to influence the output. I will be using a small 0 to 55 volt 4 digit 3 wire digital voltmeter module to display the AC volts.

 

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The challenges in using this module are that it is DC, doesn't read directly as high as I want to go, and requires an isolated power supply from the variac to do what I want it to do. I experimented with using the 8 volt and 17 volt taps on the variac to power it but I was not able to get it to zero. Finally I took an old linear 7 volt wall wart, broke it apart and used it to supply the power for the LEDs and logic. This allowed me to get accurate readings on the sense line. In the final design I used a 100K potentiometer as a voltage divider to to bring the voltage to the meter down one magnitude and then manually moved the decimal to properly reflect the real voltage. With a 4 digit display and no need for that much accuracy it left me with a good solution and the meter now displays 0 to 110 volts while actually sensing 0 to 11 volts.

 

Before I began the actual build I wanted to do some bench testing and to run some empirical measurements of current versus output temperature. For those who feel my bench is always too organized here is proof to the contrary.

 

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While I am working with some mains voltages in these tests I have taken special precautions to use isolated sources and good test procedures. Unfortunately sometimes there is just no way to make it look nice and get results in a reasonable time frame. Here is a graph of the Temperature versus Current characteristics of the heat gun. I have a very inexpensive two channel thermocouple based thermometer. I tested the thermocouple for accuracy using boiling water and ice in water. It actually tested extremely accurate considering it only cost $13.00. I placed one of the thermocouples 2 cm in front of the outlet of the heat gun and taped it in place. I wanted my readings to be consistent. Finally I fired the test up and took readings at 10 volt increments from 10 to 100 volts. I also used a second also inexpensive thermometer and you can see the difference between the black and red graph lines.

 

Temp vs Voltage Graph.jpg

 

This will give me a rough estimate of my temperature output based on the voltage shown on the meter. Once I was convinced that things would work as envisioned I began the build. I had to make the small circuit for powering the fan motor and also one to adapt the AC voltage from the variac sweeper to what would be acceptable for the meter. The small isolated power supply for the meter's electronic was already built. Here is the motor board in progress.

 

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and the salvaged wall wart:

 

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Here is the schematic for the entire unit:

 

Temp Controlled Heat Gun.bmp

The construction preceded with the customary glitches. I had a bout of dyslexia and hooked the variac up backwards on the first test. I put way too much voltage on the fan motor for a split second and had to make a repair to the motor board. By the time I got things straightened out it was 3:30 AM. Once I knew it was working I went to bed and planned to put the finishing touches on it in the morning which begins about 10:00 AM for me. Here is the finished unit. The little thermocouple thermometer is still attached in the picture as I was running final tests and I wanted to place temperature labels on the face of the unit so I wouldn't have to use the graph to convert voltage to temperature. Here is the finished unit.

 

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Finally I took a short video of how it works.

 

 

John

If you don't want to be disappointed by this blog don't read any further cause I lied.

 

The problem is that I have just signed up for a new Garbage Service. The new bin is to be left on the curb by my house in a very specific position so that the truck can come by and use its robotic arm to pick up the bin and tip it upside down to empty it. The arm then returns the bin to the curb in exactly the same position that I left it. I do not know when the truck comes so I find my self checking the bin several times a day to see if it has been dumped yet. The exercise involved in walking to the curb and looking into the bin is OK and probably actually good for me but the neighbors may notice and wonder why I am obsessed with the trash bin. I wanted a way that I could just look out my door and know immediately if the bin had been tipped or not. Here comes the Extremely Sophisticated Electronics part:

 

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OK its not that sophisticated but one has to at least admit that its simplicity is beautiful. It is powered by 4 AA batteries and uses a Tilt Switch to trigger a small SCR. The SCR turns on a RED / BLUE 1 Hz LED flasher that continues to flash until the reset button is pushed. The circuit has been built into a small plastic box and protected from rain by a sealed plastic freezer bag. Here are pictures of the unit untriggered and triggered.

 

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Before attaching the unit to the Trash Bin I called the company to see if they minded if I drilled (2) 3.175 mm holes so that I could mount the alarm. They told me "sure you can drill the holes as long as you don't mind paying for the bin". No Holes! OK. Back to the drawing board yielded an the idea to mount a bracket to the Alarm and then use a hose clamp to attach to the handle of the bin without drilling any holes or making any marks. Here is a picture of the Alarm mounted to the bin.

 

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And

 

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Now all I have to do is count the minutes until Tuesday when I can test it out.

 

John