How can i measurement a voltage under 0.5 mV

hello,

I want to try measurement voltage under 0.5 mV, so i use op amp but its still cant.

someone can help me solve this, thank you

PROGRAM.PNG

set analog reference voltiage to 1.5V (internally) or use a voltage divider to get it to ~1V.
OPAMP: you have a rail-to-rail-type?

zwieblum:
set analog reference voltiage to 1.5V (internally) or use a voltage divider to get it to ~1V.

That'd be the 1.1V reference.

OPAMP: you have a rail-to-rail-type?

Rail-to-rail refers to the output stage; OPs problem is more likely on the input stage. Not all OpAmps can handle such low voltage, it probably requires a specialised chip.

As OP obviously failed to read (or follow the instructions in, or simply ignored) the forums sticky, we get stupidity like a poorly readable screen shot of a part of their sketch, and no useful information to base any help on.

Connecting the Aref pin to 0.005volt is like shorting it to ground.
Can’t do that. You probably already have damaged the Arduino.

Put this line in setup:

analogReference(INTERNAL); // switch to internal 1.1volt reference

That should give you 0-1023 with 0 to ~1.1volt on the A/D pin.
Leo…

oops, I read "0.5V" ... anyway, please look at how to use the opamp - 0.5mV should go from opamap 0V in respect to the supply voltage of +/-4.5V.

I note your circuit seems to use a single opamp configured for a gain of 1001.

If you want a high-gain circuit for measuring a small DC voltage, a single opamp stage will not usually work well
if at all. (You get DC offset problems and instability problems). You would need a precision opamp for sure.

You should probably use an instrumentation amp circuit (3 opamps), which are conveniently available as
a single chip, and support enormous gains such as 10,000 or so, and typically have precision inputs.