Simple Issue With Ground on Circuit Connected to Raspberry Pi Zero

by Matthew   Last Updated August 13, 2019 18:25 PM

This circuit is my attempt to reiterate a circuit I already have working two times over. The circuit is an infrared detector, using a photodiode and two op amps to get the voltage and current to the level I need for a Raspberry Pi Zero to be able to read whether or not it is detecting infrared.

When I have only one infrared detector circuit connected to the Raspberry Pi, it works perfectly. When I connect two, it starts to exhibit bizarre behavior. When I shine a light at the first photodiode, the computer says the second circuit is detecting infrared, when I shine a light on the second, it says the first circuit is detecting infrared. But thats only sometimes. Sometimes, when I light up the first one, it says both are detecting light, and will get stuck saying this until I shine the light on the second one. Here is the circuit pictured below from three different angles: First picture of circuit Second picture of circuit Third picture of circuit For clarification, the blue wire from the raspberry pi is input 1, the white wire is input 2, the grey wire is a ground, and the black wire is a ground.

Here are the parts used:

-Op Amp is the LM318 from TI

-Photodiode is the SFH 213 from Osram

-Power supply is 9 Volts 1 Amp

-For each independent circuit, the furthest top is 1 Ohm, the two in the middle are 100 Ohms, and the bottom one is 100,000 Ohms.

So far I have:

-Tested each circuit independently

-Rewired, used different wires, used different photodiodes and op amps, used different resistors.

-Placed one ground wire on a separate rail and used two jumper wires to replace the independent grounds. Then placed a separate, smaller power source onto this connected ground with 1 Mega ohm resistors between the power source rails and the ground wires.

-Placed a third detector, and it took on some different strange behavior. When the 1st detector was lit up, the 1st and 3rd said they detected infrared, when the 2nd detector was lit up, the 2nd and 3rd said they detected input, and when the 3rd detector was lit up, it said only the 3rd detected input.

-Left the ground wires in but unplugged the second input wire. The first detector worked normally.

-Left the ground wires in but unplugged the first input wire. The second detector worked normally.

-Unplugged only the second input and the second ground wire, the first detector worked normally.

-Unplugged only the first input and the first ground wire, the second detector worked normally.

I apologize it is so much information, but I am at my wits end and have been working on this for quite a while and getting absolutely no where. I hope you will be able to give advice or recommendations. I am willing to try anything you might think work. If you would like a circuit schematic, I'll draw one up.

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