I'm designing a circuit for a pulse watch. Therefore I naturally have an operational amplifier and a photodiode in my circuit.
The job that I want the transimpedance amplifier to carry out is to respectively amplify the signal which is picked up by the photodiode D1 and furthermore remove noise that I would otherwise get at V_OUT.
The intention is to connect V_OUT to an analog port on my Arduino, on which I then should be able to read the current fluctuations (or is it voltage - since an transimpedance doesn't translate current).
I'm a total beginner at this, but I think that I succeeded in mapping this correctly.
However, I'm unsure that the values I gave my resistors are correct..
Let me give you my reasoning for choosing the values I chose:
Since I don't have any "negative current" in my circuit, I raised the non-inverting voltage to 2.5v by dividing the voltage with R5 and R8 - I believe that's a reasonable voltage, since I then have plenty of headroom and wouldn't cause the wave to "clip".
Next, I plan to add an ATtiny85 MCU, which (as far as I can read) has a "typical" current of 30mA per I/O pin.
There is though a place in the datasheet where it says "Analog comparator input offset current", which has a max of 40mV, but I don't really know what the parameter means.
However, I decided to put a 200Ω resistor before the V_OUT, because then at maximum output I would get something like 5/0.2=25mA. Which should be okay, and thus allows for a finer granular reading opposed to if I had e.g. a 1kΩ resistor, which would yield a maximum current of 5mA.
The photodiode I'm planning to use is: http://www.farnell.com/datasheets/8765.pdf?_ga=2.139995315.1420390384.1543406751-57595970.1536135582
And this is where things gets tricky for me. Especially, because I don't know which value to give R6, as the current across the photodiode will be dynamic.
Furthermore, I'm unsure about the capacitors.
My rationale tells me that C3 should have a relatively large farad value, as I obviously wouldn't want any noise from the gnd wire.
Also, my gut feeling tells me that I should just go with 0.1µf for both C1 and C2, but that's obviously not "optimal" in terms of limiting as much noise as possible.
To sum up:
Is this circuit correct? i.e. are my assumptions correct too?
How do I decide the values for C1, C2, R6 and C3?
And lastly, which DIP type amplifier would you choose for this job?