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1  Topics / Science and Measurement / Re: ESR meter with Arduino on: January 25, 2013, 11:43:01 am
Finally got it to work, it seems the BC327 was defective  smiley-red

Thanks for all the help!
As promised, I attach my layout and source code (built with Atmel Studio 6.0).


-- Sreg
2  Topics / Science and Measurement / Re: ESR meter with Arduino on: January 25, 2013, 06:33:00 am
Totoro,

thanks for your reply!
Sreg,
First, just to be sure we're on the same wavelength, short pins 1 and 2 on CN1 (on szmeu's schematic) together and put the  device-under-test (DUT) between these shorted pins and ground. For now, just ignore the possibility for a four-wire setup (actually three wire with the circuit from szmeu).
Yes 1+2 are shorted together amd DUT is placed between those and GND.
Quote
OK, you've done that. Now, with a 30mV pulse across your DUT, you can do the math and you should have approx. 600milliOhms +/- for the DUT. This assumes that at top of the 100 Ohm resistor, R8, (where it connects to the emitter of Q1) you see a 5V pulse.
If that's the case, then you may want to make sure that the oversampling is set up correctly for your device. You may need to change some of the register set stuff in the original code. This stuff...
  sbi(ADCSRA,ADPS2);
  cbi(ADCSRA,ADPS1);
  sbi(ADCSRA,ADPS0);
Refer to the datasheet for your device and the Atmel document that szmeu mentions.
I'm fairly sure my code is ok, but I'd be glad if you could take look at it - please see attachment.
I'm also getting about 3V pulses measured at the emitter of Q1.

Quote
Then again, it could be something simple like the discharge transistor, Q2, is always on. Or you didn't change the value of Vref in the code. You mention the internal ref on your device is 2.56V. In the code it's 1.1.
Unfortunatley the Atmega8 has only 2.56V internal reference voltage, but I think I can live with any decrease in resolution this will introduce.
My problem is that no values whatsoever are displayed when connecting the DUT as described above. (ok not entirely true, -1 is displayed since I return -1 from the calculation if millivolts are 0 - please refer to source code).
Q2 should not always be on, I get pulses on its base according to the discharge pulses.

If I get this to work, I'll gladly post my pcb layout.

-- Sreg
3  Topics / Science and Measurement / Re: ESR meter with Arduino on: January 24, 2013, 07:26:14 am
Hi all,

Since I do not have an Arduino, I have built szmeu's original circuit around an Atmega8.
The only difference is that I'm using 1N5821 instead of 1N5822.
The firmware has been adapted from Totoro's code.
When connecting a cap or small resistor across pins 1+2 and GND, I'm getting nothing, the ADC value is always 0. (2.56V internal reference)
However, when connecting a potentiometer accross +5V and GND with the wiper going to the ADC (ADC0/PC0 in my case), I'm getting values, so the ADC seems to be working ok.
Charging pulses are generated, measuring about 30mV pp at pins 1+2 (maybe too low?)
Any pointers as to what could be wrong?




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