PhotoDiode to PIC and the bit imbetween

Discussion in 'Homework Help' started by JML89, Dec 10, 2012.

  1. JML89

    Thread Starter New Member

    Dec 7, 2012
    Hello there chaps and chapettes,

    I have been asked to fill the gap between a 5microamp signal pulsing at 10238 Hz and a 5V PIC ADC Pin. The pulse is being generated by and LED and picked up by a photodiode which in turn is providing me with the above signal. I must also filter any signals that might come through from the photodiode picking up natural light.
    The parts should be available to buy and I'm able to use anything up to 12V to power the circuit
    The use of OPamps would be preferable, as I sort of understand them, but I am struggling.
    So far I have an unspecified OPamp doing a current to voltage conversion with an unspecified resistor over it, and that's it...I'm very bad with electronics and have had this sprung on me :S
    Any help would be awesome!

  2. THE_RB

    AAC Fanatic!

    Feb 11, 2008
    I think you can do it easily using any high gain opamp circuit from the internet, with enough gain so your 10kHz signal becomes a 0-5v peak to peak signal at the PIC pin and then detect the 10238Hz using software.

    You said you have a "5 microamp" signal, you need to put this through a resistor to make it a "X millivolts" signal, and capacitor couple that to the input of the opamp circuit.

    What would really help is if you show the schematic for your photodiode sensor and maybe a phot of the project or more details on the transmitter LED and the sensor and distances involved etc. We can probably help with more than just the "bit between the sensor and PIC". :)
  3. JML89

    Thread Starter New Member

    Dec 7, 2012
    I'm afraid the photodiode is "imaginary" as is the LED it is taking it's light from. The project boundaries are set at simply this is the current and this is the frequency of the pulse.
    Do I need to have a look at a possible photodiode that could be used and look into the properties or can you simply assume the current is coming from somewhere using a program like Multisim to generate a current pulse of the correct period?

    Is the gain calculation between the feedback resistor and the voltages still applicable with what is effectivly an AC signal? eg, Vout=-IinR Or do I need to use differnt formulae? Thanks!