Please help in output waveform problem from ADC connecting to DE2 board

Thread Starter


Joined Apr 9, 2010
HI, everybody.
I am doing a motor controller where signal form motor is passed to ADC and i obtain info from that point using altera DE2 board.
My question is about the ADC output waveform. I use ADS7861 ADC from Texas Instru. I use a current sensor to sense the voltage and pass to ADC with only an unity gain buffer between them.
The sensor will increase for 0.033V per 1 turn and i tried 10turns (with and without a 0.5 ration voltage divider ) and 5 turns.

Attachments are my waveform for measurements above.
I just want to ask is that my ADC not working?
If you check properly, you may found out the lower part of sinusoidal wave is working while the upper is clamped. I use the 2.5V as reference in input and i got 3.118V in DE2 software(receiver). So, there may has some unknown offset. Therefore now the offset i assume is 3.118V.

Please refer to image uploaded:

The adc work in the range of 0 to 5V. So by increase 3A where 0.99V i may got from sensor can supported by adc. (5V is the max but if 0.99V analog input, should be 3.118 + 0.99 = 4.108 which is within the range. ) Then now is the upper part is clamped while it suppose within the range of 5V.

Can anyone give me any opinion or suggestions? I feel appreciate to take any of them.

P/s: for pictures like 5T- 1.5, it is 5 turns and 1.5A by sensor. WVD-1.5 is without voltage divider at 1.5A, VD-1.5 is 1.5A having voltage divider.
If convert to voltage is 1.5A--> 0.495Vp for 10 turn and 0.2475Vp for 5 turns.


Joined Apr 5, 2008

Can you post the image here?
I do not want to wait for the delay at rapidshara and all the adds.

You can use the manage attachmets button to do so.