I have bought a KY-008 laser diode module and connected it directly to an Arduino's output pin. It has been blinking (on for 0.5 second, off for 0.5 second) for an hour. I am very puzzled.
From various sources I have read, all seem to say that a laser diode is supposed to be driven by a constant current source, and that it is a very delicate device, vulnerable to the tiniest of over-voltage.
I cannot find KY-008's schematics, so cannot be sure what is on the board. From the cheapness of it (¥2 RMB, or $0.3 USD), I assume it does not have a proper constant current source.
So, why does the laser diode seem OK (so far) driven by a voltage source (Arduino output pin)? Is the normal lifetime of a laser diode so long that even a shortened one can last for hours? Is "catastrophic optical damage" less catastrophic than it sounds? Is there something nifty on KY-008? Am I missing something?
Best Answer
I have the exact module and it does not have any complicated circuitry, just 2 resistors and a laser diode. Something like this:
As you can see, the V+ looks pretty pointless. Maybe it serves some point (like turning on the laser diode faster) but if you're just going to play with it, you don't need to connect it.
The arduino has a linear regulator, so the 5V would be pretty constant.
One of the resistors is in the circuit board of the KY-008 and one is soldered onto the laser itself. The one on the diode is the resistor in series with the diode. That resistor provides the current limiting.
With a resistor of a constant value and a power supply of a constant voltage, it ought to supply a stable current to the diode.
Thus, if the manufacturer set the resistance so that the ideal current is within the safe zone of the laser's capability, it wont blow up.
Thus it is current limited. Just make sure the voltage supply doesn't change.