measuring current from a photo diode

[mischl]

hello all

i would like to read in the brightness of light. i have a sun-wind-sensor with a build in photo diode (i think) in direction of barricade.
if i unterstod it right, the diode generate current in reference to the light. how can i measure this current (the light at the end) with my pic. i work with a 18f876a at port ra.0
in the attachment a jpg of my test, but this doesn't work allright. must i change this current to a voltage, how?

thanks for a hint

[Acetronics2]

Hi, mischl

depends on how precisely you want to measure ...

in your drawing, invert res. and diode, may be adjust a little the resistor value ... and you will have an rough idea ( linearity of photdiodes ... LOL ).

Note amorphous photo-voltaic cells, used as current generators, are pretty linear devices ...

the other way is a classical current to voltage converter around an OPA ... will be probably necessary.

Alain

[Charles Linquis]

A good explanation can be found at:



http://www.national.com/onlineseminar/2004/photodiode/photodiode.html

[mischl]

hi alain and charles

thanks a lot for the inputs.
i replaced the resistor in the schematic with a 10k and it works fine now.