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esr meter build

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hi nigel, there are several versions of the software. the reason I picked this one is that it shows three parameters of c.u.t. this is a fairly old project, I would think the designer would have corrected any bugs.
 
hi nigel, there are several versions of the software. the reason I picked this one is that it shows three parameters of c.u.t. this is a fairly old project, I would think the designer would have corrected any bugs.

If it's displaying negative values, then there's certainly got to be a software problem - as it shouldn't be able to do that - who would write a program with the capability of displaying negative values for something which can only ever be positive?.
 
It's probably using itoa(int to asc) function which will display negative numbers. This suggests that it is measuring resistance higher than 32767 which would be a circuit problem.

Mike.
 
I built three of these meters and they all have the same problem with neg esr readings. the rest of the meter works!
 
This suggests that it is measuring resistance higher than 32767
or higher than 127 if 8 bit number.
shows the esr of electrolytic capacitors as a negative value
How about taking a really good 10uF cap or 1uF that we know has low ESR, (non electrolytic) and make certain it works right.
Then solder a 1 ohm resistor in series. (0.1 ohm, or 10 ohm something small) It should read 1 ohm more.
Then increase the resistance a little at a time. I could be that at some value the number flips negative. (What Pommie said)

Can you imagine that anyone could get mixed up about signed/un-signed numbers. LOL
 
hi ron, o.k. I will do that and post back. btw, in case you haven't guessed my electronic knowledge is limited to fixing TV's.
 
o.k I got up to 65 ohms display did not turn negative. at 66 ohms the meter stopped reading esr, just a question mark.on a different tack it seems that the esr value to be correct depends a lot on what the Vesr voltage is. when its hi(180 millivolts or more it works)?
 
The meter reads in mΩ and therefor above 32Ω will display as negative. Int to Asc on microcontrollers takes a 16 bit number so it should be above 32767 that is negative.

Mike.
 
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