Electronic – Why did the laser die


I recently hooked up a cheap laser module to a mircrocontroller (via a MOSFET), mounted on top of a couple servos.


simulate this circuit – Schematic created using CircuitLab

This worked fine until I invited my coworkers to access the controls for my laser turret. One wrote a script that moved the servos from 0° to 180° and back repeatedly as quickly as possible.

Now my laser is dead. It is very dim and gets hot when power is applied, and both my cat and I are very sad.

Unfortunately, I don't have much information about the laser module itself other than what you see on the linked page. The inside looks like this:

laser top
laser bottom

So what killed the laser? My suspicion is reverse voltage from a servo motor. If that's likely the culprit, what can I do to guard against it?

Edit: As requested, a photo of the whole rig – although I'm not too sure it's very useful given the rat's nest of wires.

photo of full circuit

Best Answer

Cost = Capability

Although there are many good suggestions above, it may simply be that this laser cannot handle the stresses you've applied to it.

Electrical Stress

Your direct connection between servo and laser results in the servo feedback into the power line propagating to your laser diode.

This is what the power rail looks like when a servo is commanded to move. Note the voltage brown-outs and positive and negative edge spikes. That can damage the laser diode if it isn't sufficiently protected.

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Thermal Stress

This laser may simply not be designed to operate at the 100% duty-cycle you have applied to it. That is, it isn't designed to be able to dissipate the heat of continuous operation.

Most 100% duty-cycle lasers employ substantial thermal management devices (such as large extruded heatsinks as seen here).

enter image description here