amping a photodiode help

Roff · Aug 21, 2008

rezer said:
The 3 amplifier circuit does not look like it will work. All three diodes are in parallel. What effects one branch will effect all branches. If this is what you want, just use one op-amp. It will do the same thing.
Why not use 3 seperate photo diodes with seperate op-amps?

They are not in parallel.

rezer · Aug 21, 2008

Roff said:
They are not in parallel.

The schematic blachbunny posted showing 3 amps does show the diodes to be in parallel.

Roff · Aug 21, 2008

rezer said:
The schematic blachbunny posted showing 3 amps does show the diodes to be in parallel.

Notice he said,

u mean something like this?

That was his idea of how they should be connected. The datasheet he linked to clearly says the three diodes have a common anode connection, with the cathodes on separate pins.

rezer · Aug 21, 2008

Notice also what I said:

rezer said:
The 3 amplifier circuit does not look like it will work. All three diodes are in parallel. What effects one branch will effect all branches. If this is what you want, just use one op-amp. It will do the same thing.
Why not use 3 seperate photo diodes with seperate op-amps?

I indicated what I was talking about. I wasn't speaking about the datasheet. But no problem.

Roff · Aug 21, 2008

rezer said:
Notice also what I said:

I indicated what I was talking about. I wasn't speaking about the datasheet. But no problem.

Sorry for the misunderstanding.

blackbunny · Aug 21, 2008

Roff said:
What power supply voltage(s) do you have available? Do you have a preferred op amp? It needs to have FET inputs.

just usb bus power

Roff · Aug 22, 2008

I misinterpreted the datasheet. The part is common cathode, as you stated.
Are you going to use AVCC, or the internal 1.1V reference, for the A/D?

blackbunny · Aug 22, 2008

Roff said:
I misinterpreted the datasheet. The part is common cathode, as you stated.
Are you going to use AVCC, or the internal 1.1V reference, for the A/D?

avcc will be at 5v

Roff · Aug 22, 2008

OK, here's a place to start. You will have to play with the feedback resistor and capacitor. I have a feeling the resistor value may need to be in the megohms.
CAVEAT: I have never used the ATmega88, the LTC6082, or your photodiode.
But it's better than what you have now.

canoo · Nov 14, 2008

Hello!

I'm working on a similar project. The components I'm using are as follows:

Photodiode
**broken link removed**

The results I'm getting with the solution posted here are sorta like on off (Any light at all and the output goes low. With no light the output goes high. Very hard to reach a happy medium). I have a feeling it has to do with the resistor and capacitor in the feedback?

I'm wondering how I should go about selecting the proper resistor/capacitor combination?

Thanks in advance!

audioguru · Nov 17, 2008

Reduce the value of the feedback resistor to make the circuit less sensitive to light.

amping a photodiode help

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