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I'm trying to understand this circuit, it's been a long time since I messed with electronics.

I even managed to understand some things, for example: The first ICL7660 circuit will be used as a source to create a -9V signal.

The AD620 should pre-amplify the muscle signal.

The Capacitor and resistor in series at the output of the AD620 I did not understand.

The block with the two diodes from what I understand are rectifying the signal, but I don't understand why they are connecting between one amplifier and the other.

The RC filter on the top right is for filtering high frequencies.

Could you help me understand the blocks of the op amp?

I got to assemble this circuit but it didn't work, it has a lot of noise. Shouldn't it have a 200Hz filter?

EMG Circuit

Project source: https://stoppi-homemade-physics.de/emg/

toolic
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Airton Gomes de Lima
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    This "schematic" is a weird cross between a proper schematic and some sort of illustration. I've never seen one like it before, maybe I will have to add it to the [list](https://electronics.stackexchange.com/q/105136/2028)! – JYelton May 04 '22 at 15:57
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    EMG is a very noisy signal. – Scott Seidman Jun 04 '22 at 23:42

1 Answers1

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This is a diff amplifier with gain around 200 followed by a 1st order 100 Hz highpass filter. The two OpAmps with all these 150 k ohm resistors and diodes remove the sign of the AC signal (|x|) and the OpAmp with the 1 uF capacitor integrates it into an effective DC value. The last OpAmp stage is just a linear DC amplifier. The total gain is between 0 and 5000. I miss a 10 uF capacitor between +9 V and GND as companion for the other one.

Jens
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