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3.5mm light gates

doormat_1

Hi All,

Im looking to build a set of light gates to be able to time accurately various things and have seen in the past a homemade set using that plug into a computer via the 3.5mm jack. Then using something like audacity to measure the levels you can see the time difference between the gates.

Im guessing I can use a photodiode of some description. I just need the circuit to act as a switch either opening or closing when the light beam is broken. I can supply any voltage needed from a bench power supply.

Any ideas of a circuit diagram / components? 

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    Hi Matthew,

     

    You don't actually need a circuit, you could directly connect the photodiode to the 3.5mm jack (any orientation, both will work) and connect to the mic socket on the PC. You need a circuit to transmit modulated light however, for a suitable signal to easily detect. For that, see the talking electronics site, hit Ctrl-F and search for 'tv remote control jammer' as a suitable circuit. (In fact you could test with a TV remote control too, before building it). Basically it transmits rapid pulses of light from an LED.

    For the photodiode a BPW34-FBPW34-F would be suitable provided the LED was an infra-red one.

    This is in summary a basic light gate. If you wanted to remove the PC and have a direct output, then you could replace the photodiode with a Vishay part Vishay part (circuit diagram is in the datasheet) and continue to use the same transmitter system as before.

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  • 0

    Hi Matthew,

     

    You don't actually need a circuit, you could directly connect the photodiode to the 3.5mm jack (any orientation, both will work) and connect to the mic socket on the PC. You need a circuit to transmit modulated light however, for a suitable signal to easily detect. For that, see the talking electronics site, hit Ctrl-F and search for 'tv remote control jammer' as a suitable circuit. (In fact you could test with a TV remote control too, before building it). Basically it transmits rapid pulses of light from an LED.

    For the photodiode a BPW34-FBPW34-F would be suitable provided the LED was an infra-red one.

    This is in summary a basic light gate. If you wanted to remove the PC and have a direct output, then you could replace the photodiode with a Vishay part Vishay part (circuit diagram is in the datasheet) and continue to use the same transmitter system as before.

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