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mecdub asked in Science & MathematicsEngineering · 1 decade ago

How do I build a break beam sensor?

It's supposed to be similar to the sensor used in home security or the buzzers on convenience store doors. We have 10 ohm resistor connected to a brite LED on one circuit board, and a 1k resistor connected to a CdS photocell on the other. This setup gave a signal when connected to an oscilloscope. Now we can't figure out how to connect the CdS cell to a buzzer.

1 Answer

  • 1 decade ago
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    You need some sort of current buffer or relay between the photocell and buzzer. The buzzer operates at a much higher current than the photocell.

    A power FET might be useful here with the point which you monitored on the oscilloscope connected to the gate and the buzzer in series with the drain circuit. Many other devices could be used but all will essentially amplify the current available from the photocell circuit. Sorry I can't post a diagram!

    Also, if you need the buzzer to remain activated after the beam continuity is restored you will need to add some sort of timer or latch circuitry.


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