Emitter and receiver optical signal with transimpedance

Thread Starter

victoriomariani

Joined Nov 8, 2023
7
Hello fellow electronics enthusiasts,

I'm seeking some advice regarding an issue I've encountered with an electromagnetic wave emitter. Despite covering the photodiodes, I'm still detecting a signal at the same excitation frequency as the LEDs. The emitter and receiver circuit are show here.


1711196004997.png1711195759040.png

The square wave is generated through the ESP32 and the symmetrical source (+9V; -9V) that feeds the emitter is the same that feeds the OPAMP. I have the problem that even though the photodiode receives light, there is an output signal, and this output signal is the one generated by the microcontroller. What will be the problem?

I'd greatly appreciate any insights or suggestions you might have regarding this issue. Additionally, if anyone has encountered similar challenges or has experience in troubleshooting electromagnetic wave emitters, your input would be invaluable.

Thank you in advance for your assistance!
 

Sensacell

Joined Jun 19, 2012
3,471
This is a classic design problem.
You have a huge signal (TX) and you are looking for a tiny signal (RX) and these two things must live together in your system, and the levels can differ by 120db or more.

You need to do all of the following:

Reduce the amount of energy that leaks from the TX using shielding, physical separation, supply decoupling etc.

At the same time you must protect the RX from receiving unwanted energy by the same methods above.

The power supply must have great filtering employed between both systems too.

It might take all of the measures together to solve the problem
 

Thread Starter

victoriomariani

Joined Nov 8, 2023
7
This is a classic design problem.
You have a huge signal (TX) and you are looking for a tiny signal (RX) and these two things must live together in your system, and the levels can differ by 120db or more.

You need to do all of the following:

Reduce the amount of energy that leaks from the TX using shielding, physical separation, supply decoupling etc.

At the same time you must protect the RX from receiving unwanted energy by the same methods above.

The power supply must have great filtering employed between both systems too.

It might take all of the measures together to solve the problem
A decoupled capacitance at source is a good solution?
 

AnalogKid

Joined Aug 1, 2013
11,126
Also, isolate the two circuits' power sources. If they have to be powered by the same supplies, run separate lines (home runs) to each circuit directly from the supply output terminals. In this way, there are minimal wire lengths carrying current for both circuits. This is especially important for ground runs.

ak
 

MisterBill2

Joined Jan 23, 2018
18,934
First, I do not see any circuit of an electromagnetic wave transmitter. I see a circuit pulsing an array of LED devices.
I see also a small portion of a photo-diode detector circuit with no power connected.
I am guessing that the supplies are 9 volt batteries.

Posts #2, #3, and #4 are correct, but still without more details there is no point in my considering how to solve the problem.
 
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