Help with pH circuit

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Thread Starter


Joined Jun 11, 2020
Hi all,

I posted a similar question a little while ago here

I have since acquired all materials to make this circuit shown below. Full walk through

My circuit is exactly the same and I do not get a reading.

When I connected a single 9v battery instead of 2 i was able to get a constant 1.4 volts across the pins. I am using pins 1 2 3 4 5. I measure across pins 1 and 4.

Ive been troubleshooting all day today and i cant seem to figure out what i am doing wrong. I started a new thread because the old one was answered and it seems to have gone off on a tangent.

My end goal with this circuit is to have it light up an LED when Acid is detected.


Joined Dec 29, 2008
... Not quite sure if this is relevant, but is the op-amp powered up before the input voltage is applied? ... Read something about how the op-amp could be damaged if voltage is applied at the input prior to the placement of DC power at the appropriate pins.
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