How to use Op amp with photodiode

Other Hardware General Electronics
1

Hi,

Essentially all I want to do is measure the amount of light and display it on the board. However I have the issue of the wrong amount of sensitivity - if that makes sense.

I want to use an op amp to amplify the signal (in an inverting fashion? with negative feedback) . I need this so i get a nicer spread out range of values.

I dont really know how to make this into a circuit

I think my gain is dependent on two resistors .

I believe in an inverting amp Vo/Vi = - R2/R1

What op amp should i use LM741?

Any help would be great

2

Measure the photocurrent, not the voltage, using this kind of circuit:

One resistor to set the gain.

741 is literally over 50 years old, quite hopeless for 5V work as
its designed for +/- 15V supplies.

3

How do i measure photocurrent if im getting Vout?

What op amp would you suggest then?

And where do i use the 5v input from the board? does it go into the amplifier or into the photodiode?

4

There are hundreds of Op-amps I tend to use the MCP602

How do i measure photocurrent if im getting Vout?

The Vout IS a measure of photo current.

And where do i use the 5v input from the board?

The op amp has power and ground you connect that to the 5V and ground of the Arduino.

Last warning.

DO NOT CROSS POST

5

MarkT:

Nice colored diagram! May I ask which software did you use? :wink:

6

MarkT:
Measure the photocurrent, not the voltage, using this kind of circuit:

Will that work, or will it work effectively, without a negative bias on the diode, and is the Is arrow the wrong way round (at least as indicating the actual direction of the current)?

7

Here is an excellent reference on the design and use of photodiode amplifiers: http://ecee.colorado.edu/~ecen4827/hw/hw1/PhotodiodeAmplifers.pdf

8

Deja vu.

9

Please don't post the same question twice.

http://forum.arduino.cc/index.php?topic=276707.msg1948599;topicseen#new