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1  Topics / Science and Measurement / Re: ESR meter with Arduino on: July 22, 2012, 03:48:12 pm
That's it! 
With "esrVal = (miliVolt * 100)/(4.9-(miliVolt/100)); "  I get 339 on the 1/3 Ohm resistor, 987 on the 1 Ohm and 6582 on the 10 Ohm.  My 10V-2200uF good-cap, bad-cap pair now read 21 and 3774 respectively.  Perfect!  I didn't mention the diodes in my first post as they are the same as you used. I just wanted to verify your PCB works, as do homemade non-polar caps and 2N2222 / 2N2907 transistors.

This is such a useful tool; and so cheap and easy to build.  I really hope others build this, make their own modifications, and post their results.  If the arduino has enough processing power it would be great to have an audible tone to check caps without looking at the LCD. When I have more time I hope to learn how your code works and make the circuit in Eagle Cad so I can experiment.  Thanks again for posting this great project and all your help.   
2  Topics / Science and Measurement / Re: ESR meter with Arduino on: July 19, 2012, 09:36:36 am
Thanks for the reply szmeu.  
I did find the problem, and it was me...  I checked my circuit and for R8 (on the PCB) and found 1 Ohm rather than a 100.  I must have put my 1 Ohms and 100 Ohms in the same bag  last time I cleaned up ;-)   After the fix I calibrated using the original code until I got 1001 on a 1 Ohm resistor. The 1/3 Ohm reads 363, and a 10 Ohm reads 4450 (it's all I have to test with).  Am I correct in assuming this pretty accurate and the 10 Ohm is just too big?   I tried the voltage divider modification, but it gives negative numbers (-112 and -143).  Thanks again for the great code, and sorry for the confusion.  I think this is an extremely useful tool and have built both an arduino shield and a self-contained ardweeny powered meter housed in an old external hard drive case. 

3  Topics / Science and Measurement / Re: ESR meter with Arduino on: July 15, 2012, 03:41:02 pm
Thank you for sharing your excellent circuit and code.  I made a PCB from your circuit image and used 2n2222 & 2N2907 transistors and 1% resistors. I didn’t have a non-polar cap, so I soldered the anodes of two 100uF caps together.  As a test, I tried adding parallel diodes to the caps, but found they made no difference in my readings.   On a pair of used 2200uF 10V caps I got 0.0 Ohms on one that looks good, and 5.600 Ohms on one with a slight top bulge, so it finds bad caps.

The problem I am having is that I am unable to calibrate it.  Using a one Ohm resistor I had to set “double current = 0.007460;” to get the meter to read 1.012, but then a 1/3 Ohm resistor reads .090.  Could the transistors or DIY capacitor cause this?   I'm a beginner, so your post was highly educational and I got a new test tool as well!  Thanks again.

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