Hello, I want to make a laser pointer as the first project with my microbit v1.
From before I only have the microbit itself (no other components), and I have now ordered a 2x AAA battery pack with a PH2.0 connector for the board to make it a wireless unit.
Now I need to source a laser diode. On eBay I found some so called "3 V laser diode modules with drivers". Some of the specs:
Wavelength: 650 nm
Output Power: 1 mW
Working Voltage: 3 V
Working Current: < 20 mA
Laser Shape: Dot
Focusable: Yes
Material and Color: Brass
Lens: Plastic
Dimensions: Ø 6.0 x 10.0 mm
It plan to use it for prolonged use for pointing on a projection screen or a white wall, and I want it to be eye safe for such use.
There is also a similar laser diode on eBay, with identical specs except the only listed difference being a working current of < 40 mA instead.
Now, 3 V x 40 mA =120 mW and 3 V x 20 mA =60 mW.
Will it make a difference if I choose the 20 mA or the 40 mA version? Both claim to be 1 mW!
Do anyone have any idea how large the difference should be between power draw and emitted power?
I should mention that I saw a video on YouTube ("Are Cheap 1mW Lasers Really 1mW?") where many lasers marketed as "1 milliwatt" were measured to be much higher in their light output (28, 56 and 79 mW for the "1 mW" lasers tested in the video). Does this make them dangerous to the eye?
Finally, important question: Can I drive such a laser diode directly using a PWM output from the microbit? I read that the maximum power draw on these pins was 3.3 volt and 100 mA each, so I think the power limit should be okay. But will the laser diode accept PWM pulses? Perhaps I can use the PWM to dim the laser if it is too bright?