Reading voltages at the screw input terminals

Question

Reading voltages at the screw input terminals

Closed this issue 6 years ago · 3 comments

Hello,
first of all, great work on this. It works quite nicely out of the box. Since I am a newbie when it comes to hardware programming / RPi I have some questions regarding on how to use this code to read out voltages at the screw terminals:

I want to read out 8 single-ended voltages on the screw terminals AD0 to AD7 compared to ground. Somehow, when I run your example.py I get the Poti_CH0 and LDR_CH1 voltages (I connected the respective jumpers on the right side: VCC=5V=VREF, ADJ on AD0, LDR on AD1, AINCOM on AGND) but then the other channels (AIN2, AIN3,..) show some random values. When I now connect let's say 0.8 V signal to screw terminal AD2 I'm expecting to see AIN2 to go to 0.8 V but it doesn't. My question is:
How do I define the channels at the screw terminals AD0 to AD7 to be read out single-endedly with respect to ground?

I'm sorry if this is straight forward and I'm just to blind to see.
Cheers

Answer 1 · 2018-07-19T23:13:45.000Z

Hi, with the example configuration, this should work out of the box:
EXT2, EXT3, EXT4 = POS_AIN2|NEG_AINCOM, POS_AIN3|NEG_AINCOM, POS_AIN4|NEG_AINCOM

Did you connect the GND wire of the 0.8V voltage source to AINCOM/AGND?

Answer 2 · 2018-07-20T05:28:58.000Z

Hi, thank you for the reply. I did not do that because I assumed since the RPi GND jumper was set it would compare the 0.8 V to (some) ground. Should I connect the 0.8 volt s ground to the GND screw terminal then? You might as well label this issue as `question`. In will try everything on Monday! Have a nice weekend! Cheers

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On 20.07.2018 at 01:13, <ul-gh> wrote: Hi, with the example configuration, this should work out of the box: EXT2, EXT3, EXT4 = POS_AIN2|NEG_AINCOM, POS_AIN3|NEG_AINCOM, POS_AIN4|NEG_AINCOM Did you connect the GND wire of the 0.8V voltage source to AINCOM/AGND? — You are receiving this because you authored the thread. Reply to this email directly, view it on GitHub, or mute the thread.

Answer 3 · 2018-07-25T10:17:37.000Z

Hi,
everything works fine now. In my hurry I didn't connect ground at all so as you pointed out that was my mistake. Thanks!