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Raspberry PI - Ohmmeter

Posted by sherbieny Sep 23, 2017

An Ohmmeter device using Raspberry PI 2B with ADS1015 as ADC


  • Items needed:
    • PC or Laptop
    • Raspberry Pi (I used model 2B)
    • ADS1015 12bit ADC converter (if you use 1115 which is 16bit, there will be slight changes)
      • Breadbord, wires, resistors
      • Adafruit assembled Pi T-Cobbler Plus - GPIO Breakout (Optional)
  • Circuit setup
    • Refer to fritzing diagrams in schematics folder
  • Configuration
    • SSH, VNC or anyother method of communication enabled between the Raspberry PI and the user PC
      • My case was
        • Laptop with Ubuntu 16.04 LTS
        • Raspberry PI 2B with Raspbian Jessie release 2017-01-11-raspbian-jessie.img
        • SSH communication through ethernet cable
  • Deployment instructions
    • As per the schematics folder
      • Connect Raspberry with Adafruit T-Cobbler
      • Connect T-Cobbler onto the breadboard
      • Connect ADS1015 onto the breadboard
      • Do the wirings as described in the schematics folder
      • In the circuit diagram I made a note about the location of the UNKNOWN resistor Sources With

  • VIM text editor
  • GCC compiler

I started this post as a Wifi Analyzer... but the more I got into it the more it became a complete handheld network analyzer for wireless as well as wired for performing basic network functions such as speed tests and pings, on up to measuring signal strength and identifying noise.


Here are the requirements:


  • Small form factor (hand held) not much larger than your palm (5 in. screen range), I'm thinking a strap across the back side of your hand
  • 4 hour minimum rechargeable battery
  • Touch screen
  • measure dBm/SnR and log/graph over time appropriately
  • function for measuring attenuation
  • Channel identification
  • Googleing I found a couple of build guides for more inspiration - A complete network analysis tool for the Pi (NetPi) and a spectrum analyzer from Adafruit
  • It would also be cool to bring in a floor plan and plot your measurements on the floor plan as a baseline for future testing
  • Need access to wired NIC for using network analysis tools from data-center or data closets



Sounds like a Pi 3 (how to handle 5Ghz? usb wifi dongle? need external antenna? gig Ethernet NIC dongle? maybe someone knows of a better solution than the Pi?) and a 5 in touch screen, a touch interface GUI as launcher for multiple software packages, LiPo or Li-Ion and charging circuit, 3d printed ergo palm enclosure (see into my brain below). 


What you think? Suggestions, ways to expand?

Image result for palm strap ipad

Hi i resently got an idea after learning about freenas interface web based I learned that freenas lets you to turn off your computer form the web so i was thinking is it possible to turn the comouter on by the web interface so i tryed to solve this problum.

and i was woundering is it possible to have the raspberry turn on my computer by web interface system useing the pins that it had i am well ware of that i could not do this by raspberry ip and a computer i would need a modual to try this out.


I just wanted to share this idea with you guys and hope that you could make a video about it. ps sry for the bad english and grammer.


Thank you for reading this.

in the office building I work we have DIY addressable led strips surrounding every floor of the building to make it glow at night. It's a part of my job to maintain this setup and unfortunately the setup breaks down a lot.


We we got a defect then I have to open up the sealing and get the 3m long led bar out and take it to the warehouse to test the led strip. I have already bought a wireless soldering iron so I can do small repairs without taking the led strip out of the sealing, but I still need to get it out if I want to connect it to the test unit.


It would really be great if I would have sort of a portable addressable led strip tester, that can run the following tests

- put all led's to red

- put all led's to green

- put all led's to blue

- put all led's to white

- slow nightrider mode 1 led at a time

- put all led's to black (off)


this would save me a lot of time and I guess it would be a great tool for everyone that uses addressable led strips in there projects

I'm trying to figure out a way to make such tester, but the main problem I have is how to deliver enough power for the 3 meter long led strip?

How about building a Raspberry Pi universal multimeter and oscilloscope. You could use the bitscope mod and if you can create a application you can make a multimeter app to measure voltage, resistance and current (Or even a LCR function)

This is my submission to the Element14 Project14 DIY


The problem

I have recently been doing extensive experimentation with recycled batteries as well as voltage regulators and line control circuits. The customary approach requires a programmable DC load to the connected such that the output can be tested under various conditions. Unfortunately, these commercial solutions are quite expensive in addition to being big and bulky. Due to a constant fear of the spouse with regards to unexplained expenditures as well as a lack of bench space, I set out to find a DIY solution to the problem.


The result is a simple yet elegant project that can be assembled in a manner of hours and is useful for all electronic hobbyists and professionals alike. Due to a reduction in size and very low BOM cost, the device can be used for field testing of a number of equipment as well. In the writing below, I will try to explain the research process, accepted approach, assembly as well as a quick demo of the project.


The search

Doing a google search for ‘constant current source’ comes up with a number of interesting results including publications in instructables. Though these may not inspire much confidence, they are a source of test data that an approach was in fact used. My search lead me to a youtube video by Dave Jones of the EEVBlog where he uses a simple circuit to make a DIY Constant Current Load. Further investigation revealed that many more had tried the approach and indeed was a usable. Hence, I decided to recreate the circuit shown below due to it’s simplicity.





The tweaks

The selected low-side sensing and control approach was solid however, I had to improvise a bit in my approach with the first change being the MOSFET itself. The MTP3055 was not something I had to hand so I decided to use the IRFZ44N. This had a cascading effect on the design with the Vcc being migrated to 9V and eventually two 9V cells. I used the LM358 which is half the op-amp the LM324 is however retains all the characteristics. Lastly I only had 1/4watt resistors which I had to make do with but did not make a big difference in the long run. I also did not want to spend on a dedicated meter hence resorted to other means. The final improvisation in the assembly is the use of a multi turn preset in place of the suggested multi turn pot which is cheaper and more compact.


The Circuit Diagram

Below is a shot of my notebook with the circuit diagram, specs and a layout. I used separate connectors for the Op-Amp supply and the load. In order to monitor the set current, tapped into the non-inverting input of the second op-amp. This connected to a multimeter would give us the set current without the need for a dedicated meter thus reducing the BOM cost of the project. An extension of this technique could tap into the inverting input to get the value of actual current being drawn. In my case, I employ a dedicated meter for the task to ensure accuracy.





Adding a fuse or switch seemed trivial though can be a useful feature. I do not plan to make a PCB for this since it is a stepping stone to the next level which I will discuss at the end. I made a layout of the design before I switched on the soldering iron so that I knew exactly what I would be aiming for. I aimed to made the device as small as possible and in true DIY fashion.


The Assembly

Putting humpty-dumpty together was not a challenge thanks to a bit of planning and the end result is presented in the image below.




With my 3D printer lacking the necessary filament, I decided to add some DIY stand offs to the resulting circuit board. Pencil erasers cut up in the right size and attached using hot glue were a successful endeavour allowing for a bit of ground clearance. This would be helpful in case of solder blobs or unsheathed wire trims were loose on the workbench. The heatsink was a non branded one though it did seemed big enough and did it’s job well. The end result is shown below without it’s connectors as well as in complete setup.






My tests were conducted with a Tenma Bench Power supply at 12 Volts though I did do the math before hand. Below is a capture of my workbook reflecting the same.



Sincethe IRFZ44N is capable of working up to 175’C and 50Watts, my tests would be a piece of cake. Below is a video of the entire project along with a demo of the final product.



One point to be noted is that at 1 Amp of current, the drop on Rsense would be 1 Volt and with the Vgs required to be more than 10V for the IRFZ44N and 4.5V for the MTP3055, the gate voltage should be as high as possible. This would also go on to effect the switching times with the Vgs rise time not being able to meet it’s intended mark.



More Notes and future work

I designed this module to work as a standalone project however there are a number of things that can be done in the future. The first being the addition of an Totem-Pole Driver stage to the MOSFET to increase switching speed. This is easier said than done however it addresses the issue raised in the previous section.


The second modification is using a DAC to digitally control the set current. The buffer could be converted into a gain stage and it could be digitally controlled. Next would be the addition of an ADC to monitor the actual current flowing. An INA219 could be used directly if the circuit were to be made anew and on a dedicated PCB.


Lastly, a self resetting fuse and temperature sensor could be a handy feature for long term use. A DS1307 could be used for the RTC and store current and voltage data until it is retrieved. This could be furthered by the addition of a memory card hence the possibilities are endless.



peteroakes jancumps and jw0752 already have an extensive project in the making for the more serious user. This is a quick and dirty solution for the procrastinating maker and enthusiasts and I hope it finds use in your hobby shop.



Happy Hacking!