Question abou wiring up laser pointers for projection

  • Hey dear Duetdudes,

    i have a question about the wiring of laser modules i bought for my project i am building up. I have a Duet 2 up and running fine and now in my machine i like to install three low consumption laser diodes with red point. I dont want to do things like engraving or cutting and i dont want to use them as end stops. They have another use case.

    The diodes run at 2.7 to 3.3 volts and draw each 30mA. They generate 1mW of power to project a point of ~3-5mm at 2 to 3 meters distance. I want to use those diodes to generate some measurement/helper markings in the machine frame. I selected those diodes because they have 635 nm of emitting light which is good for visibilty. in my use case i also had to select for class 2 laser light and for less output to be secure to eyes. and i needed some focusable light. full specs:

    Because i dont want to keep them active all the time i am thinking how to wire them best - now as i have got them and tested them with some batteries. Do you have any recommendations on how to wire up best with Duet? I thought about PWM controlling to turn them on/off. I have no expansion boards, just the Duet.

    my ideas so far:

    • make use of 3.3 Volts of the end stop connectors -> do the end stop outouts survive 30 mA or in total 90 mA?
    • 24 volts of VIN + some step down module to convert 24v down to 3.3V and then to connect directly to a FAN connector. the 90mA should be totally no problem here because usual fans have 0.1 A or more
    • some GPIO pin + some transistor logic to turn on/off the diodes. I read about 4 free to use pins on Duet which can be used freely (which i did not find on the Duet drawing yet)
    • wire up to my Raspberry Pi 3 instead (GPIO will not survice 90 mA because total maximum allowed s 50mA). any idea here maybe?

    all diodes should be on/off together. i dont need to switch them on/off individually.

    i want to install with less electronics as possible. i am happy to get your feedback, critics, ideas, whatever 😄

    thanks, Mario 🙂

  • administrators

    @vmario89 said in Question abou wiring up laser pointers for projection:

    make use of 3.3 Volts of the end stop connectors -> do the end stop outouts survive 30 mA or in total 90 mA?

    you cant source or sink 30 mA from an endstop or other normal IO pin directly. The datasheet for the microprocessor is here:
    The table you want is on page 1355

    in this case you may find the easiest option is to use one of the fan outputs to switch the ground side of the circuit with the lasers on it, and then supply the 3.3V either from an endstop header or the expansion header.

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