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Changed the resistance from 470 kOhm to 50 kOhm.
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I forgot to draw, but the 100 nanofarad capacitors were already soldered.
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I disconnected all the incoming circuits where there are 1 kOhm resistors, protective diodes, they are not shown on the board for a better understanding of the circuit, and shorted the chip inputs +IN and -IN and to the midpoint.
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Positive track and negative track can not yet quickly make, it is necessary to completely redesign the board, the idea is good, I like it, I will apply.
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For the whole board I made an iron box, a screen, and soldered the middle power point to the screen.
Unfortunately the result is not noticeable. I expected better. I bought the microchips on digikey.
I needed them to amplify the biopotentials of the head, and it worked. I put two electrodes on my head, one on my ear.
And when you blink your eyes, you can see it on the oscilloscope.
But here recently I learned about the beautiful characteristics of the AD8428 chip which is connected in parallel four pieces to reduce noise.
No Pain High Gain: Building a Low-Noise Instrumentation Amplifier with Nanovolt Sensitivity
AD8428 datasheet
Low noise: 1.5 nV/√Hz input voltage noise
And the AD8422 has 8 nV noise.
Let four AD8428’s give 10 times less noise.
And theoretically I will get 80 millivolts at 100000 times gain. I’d like to do better.
So before buying the AD8428 I decided to deal with my AD8428, which has good characteristics according to the datasheet, and it seems to be less noisy, let’s say 100 times, it would suit me.
At the moment I’m using the AD8422 chip not only for taking head biopotentials, but also for photodiode, phototransistor.
So if you’re into that, can you recommend an amplifier for the photodiode, it’s kind of a transimpedance amplifier.
I’d like to have a million times gain with minimal noise. 1000000 times. For example, two chips in series amplify each by a factor of 1000. If the noise is 1 nanovolt, ideally I would like to have noise at 1000000 times gain of only 1 millivolt.
Suppose I connected two amplifiers in series, short-circuited the inputs so that no signal gets through, and I get 1 millivolt at the output, that would be cool. Is there a solution to that? Can you help me find it? Or as low noise as possible, like down to 10 millivolts. So that I really soldered, and I worked, please if there is a solution, offer knowledgeable and knowledgeable in this. And it is desirable to be able to adjust the gain.
