0
\$\begingroup\$

I have set up my raspberry pi to read from the MAX1204. To know if I'm reading the proper value, I use a multimeter at the input channel of the ADC, and compare it to what I read through my program. This works great. However, when I disconnect my multimeter, I don't read the same value. If I was reading 1.264 - 1.268 (correct measurement), I now read 1.248- 1.252.

I assume it's due to the internal capacitance of the multimeter, or some other reason. How can I set up a capactiance or a way to read the correct readings without constantly needing to have the multimeter plugged in? I tried using a 0.01uF, 0.1uF and no luck.

Block Diagram (to try and replicate schematic):

enter image description here

Edit: it would seem that when changing my multimeter to the 2V option va the 20V, thé close it 1.276 but the ADC is still reading 1.25. Which means I have a 25 mV difference between voltage and readings.

\$\endgroup\$
  • 1
    \$\begingroup\$ What is the source of the voltage you are measuring and its source impedance? What is the internal impedance of your multimeter? (usually 10M\$\Omega\$ or 1M\$\Omega\$). \$\endgroup\$ – Spehro Pefhany Feb 12 at 1:24
  • \$\begingroup\$ The voltage is measured after several buffers. My multimeters is this one: rcce.com/rcc507-digital-multimeter , not exactly sure how to find the impendence \$\endgroup\$ – George Feb 12 at 1:31
  • 1
    \$\begingroup\$ Have you looked at the signal with an oscilloscope? \$\endgroup\$ – Spehro Pefhany Feb 12 at 1:33
  • 1
    \$\begingroup\$ I understand you believe it to be a DC voltage, but it would be nice to confirm it. \$\endgroup\$ – Spehro Pefhany Feb 12 at 1:46
  • 2
    \$\begingroup\$ Schematic != block diagram \$\endgroup\$ – Spehro Pefhany Feb 12 at 2:10

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Browse other questions tagged or ask your own question.