Analog Inputs and Digital Value

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1

Hi, I am new to playing with electronics, but I have a velleman k8055, it works great but for the analog input.
I have a device which gives me a voltage between 0-3.3V, and would like to see it converted to a digital value.
But when my analog device gives me a voltage, for example 2.13V measured as an input to A1 on the velleman board, the read analog call returns a value of 60. I would expect 2.13V/5V * 255 = 108. Can you please explain this? I did try testing the board manually w/ the 0-5V pot. and it works great when set at 2.13V.

Thanks!

2

Have you set the trimmer potentiometers ATT1 and ATT2 to max position clockwise?

3

Hi, thanks that was it!

Would you be able to also tell my the differences in analog control voltage? i.e. I send 110 down, which I would expect to be 110/255*5V = 2.16V, but when I measure it, the velleman is outputting 1.91V instead. Thanks!

4

The output voltage is directly proportional to the +5V supply voltage.
Furthermore the output never can go up to +5V due to the output operational amplifier limitations.
The maximum output voltage is about 4.5V.