thanks for your reply!
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.
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...
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.
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.