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Why does the brightness of the ky-008 laser head sensor module differ greatly between being connected directly to the 3.3V power rail of a bread board and to a GPIO pin?

The laser emits a very bright beam and a "star field" around it when connected directly to power or two AA batteries in series, but a small, tight beam when powered by a "HIGH" pin. From what I read the GPIO pins should operate at 3.3V.

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  • Be careful, to overload a GPIO can damage it beyond repair and in worst case fry your Raspberry Pi.
    – MatsK
    Commented Sep 3, 2017 at 19:09

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It is likely that the current the Raspberry Pi's GPIO pin provides is too low for the laser diode to operate properly.

I did not find a data sheet for the laser diode, but this page claims 30 mA at 5V.

The Raspberry Pi's GPIO pins however have a limited capability to support high current, see here: Maximum current on each GPIO pin for Raspberry Pi 3 Model B

The party line has always been that you shouldn't draw more than 16 mA from an individual GPIO or more than 50 mA from the GPIO as a whole.

It might thus be necessary to use an additional transistor to control the laser diode from the GPIO pin, see here: How to control a 3V laser from GPIO

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  • I should have said it seems to operate better on the gpio, on battery it is kind of a scattered beam. I'll check out those links when I get back to my PC.
    – Crowcoder
    Commented Sep 3, 2017 at 20:30
  • @Crowcoder it might very well be that it is significantly underpowered from the GPIO pin and thus much less bright than with another power supply. Maybe what you see there is "speckles" a phenomenon that comes with lasers.
    – Ghanima ♦
    Commented Sep 4, 2017 at 18:14

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