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):

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.

• 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$\Omega$). – Spehro Pefhany Feb 12 at 1:24
• 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 – George Feb 12 at 1:31
• Have you looked at the signal with an oscilloscope? – Spehro Pefhany Feb 12 at 1:33
• I understand you believe it to be a DC voltage, but it would be nice to confirm it. – Spehro Pefhany Feb 12 at 1:46
• Schematic != block diagram – Spehro Pefhany Feb 12 at 2:10