[Grbl_Esp32 Issue#155] Connecting to diode laser

#1 – easytarget 于 2019-10-13

Edit: This is rather old, but with a reasonable answer maybe it can be closed:

Option 3. A TTL chip (74 series) is generally recommended. But mosfets and optoisolators are just as good.

Your bigger laser is probably a pure TTL PWM line (high impedance) and cannot overvoltage, nor overload the ESP pin. A 3.3 float voltage is very typical on them. This is the only sort that can be directly connected to 3.3v electronics. And I’d argue that even for this you should have some sort of buffer if using anything more expensive than an ESP chip controller(*)

The Smaller laser sounds like basic PWM unit, with a resistor pulling the pin to some internal +Ve, 5.7V is a common voltage for the actual diode. This means it is low impedance and providing a (relatively) high current at that voltage. More than enough to burn out the ESP’s input.

For this unit both your solutions 1 and 2 probably work, but I’d personally not risk it. I’d add a circuit with an optoisolator to drive this (but I have a bag of optoisolators on my desk, so that’s easy for me to say), a simple mosfet or other npn pulldown would work just as well.

Try to limit capacitance in whatever you do, one of the secrets to clean laser cutting seems (this is just my opinion after seeing it discussed on CNC forums) to be a nice sharp square wave on the Laser. It’s the reason why 74 Series TTL logic chips are sometime recommended, they have a very clean output.