How to make a simple laser controlled gate?

hi! we've got this project at school to make an electronics circuit with mechanical output. the 1st circuit we've done was a laser controlled on/off switch for bulb which perfectly operates using 2 LDR,12V relay and 555 timer. So we have to use this circuit with a reversible dc motor and maybe additional components to mechanically close or open a gate.

So the output should be like this, when i light the laser pointer to the 1st LDR, the gate will open, and when i light it to the 2nd LDR the gate will be closed.

and that's where i'm having a problem. Its our first time to use a motor with electronics circuits and i don't know where to connect everything.. I hope you can help.

Thanks in advance! :)

This is what our first circuit looks like:

3 Answers

  • steve
    Lv 7
    6 years ago
    Favorite Answer

    You need to check the datasheets for the LDRs to make sure that they will respond to the wavelength of the laser that you are using and that they will give you the dynamic range that you are looking for the LDRs (laser on low resistance, laser off high resistance). Also what about the ambient lighting? Is that overpowering the laser light? The LDRs are designed for ambient visible light typically, not laser diode light.

    In addition, there will need to be some small amount of current to flow and using 1 Meg resistors will probably make the comparators unstable.

    Finally the snubber diode is configured wrong (inverted) and the relay will not turn on, or will burn out after the field in the coil collapses. D2 needs to be reverse biased against the output (cathode into the output), so that when the 555 is off the magnetic field will flow around D2 and the coil. D2 is used to recirculate the magentic field current when the 555 timer output transistor turns off. Your circuit may already be damaged from this; both the 555 and the relay.

    Source(s): vast engineering experience.
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  • Colin
    Lv 7
    6 years ago

    If the diagram at the bottom of the link is correct (see "Bistable mode") that would be a basis for what you want.

    Replace the resistors marked as R with 1 megohm resistors, and the switches with the LDRs.

    As in your present circuit, connect the relay and diodes from pin 3 to the 0v line.

    Light on the LDR connected to pin 2 would sent the output high; on the other would send it low again.

    I have *not* tested such a circuit.

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  • 6 years ago

    Replace the power source where marked 230V at the contacts from relay with 6V DC power source.

    Connect a 6V DC motor to the place where it marked LOAD shall do.

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