Wiring for new Cohesion3D laser board

Machine: K40

Board: laserboard replacing an arduino + ramps that replaced a moshi board

Firmware: “I have a new board and I’m using whatever it came with”

Problem/ Question: Just got my new laser board in the mail and I am trying to install it. I got the stepper and endstops connections figured out but I am confused about the laser fire/PWM connection. This is the PSU I have - http://www.everythinglasers.com/wp-content/sp-resources/forum-image-uploads/scottmarshall/2016/11/WhitePSU-pinout.JPG

The moshi board I had took (other than steppers and endstops) 3 wires - 24V in, GND, and laser fire (not PWM). The arduino setup that I replaced moshi with connected to both laser fire and laser PWM.

From the limited laserboard documentation, it is not clear to me where to connect the two PWM pins (the top of the two marked not used). The documentation suggests to connect it to laser fire, but shouldn’t the bottom pin simply go to the 0-5v IN terminal on the PSU? Where does the board draw the 5V from in order to feed the 5V in? A schematic of the board might be helpful…

The PWM functionality rapidly connects laser fire and GND. Connect GND to the GND terminal on the laserboard and laser fire to L on the laserboard.

Gotcha, and don’t connect the laser PWM to anything? or leave it connected to the potentiometer? How is the amount of power to the laser controlled, since the laser fire (L) is binary on or off?

The potentiometer should be connected to the LPSU’s 5V, IN, and GND terminals. The pot in this case controls maximum laser power, and in most cases should be set to your tube’s maximum output current (15-18mA for a stock K40). If you’re doing more sensitive engraving you can achieve better results sometimes by backing the max tube current off and taking advantage of higher resolution of the remaining power through software control.

The two “alternate PWM” pins (which I believe you’re referring to here) in this case are not used. Those are for certain types of diode lasers that are powered separately but controlled via a 5V PWM signal.

Here’s what’s going on - the PWM signal generated by the laserboard fires both those “alternate PWM” pins, and an optoisolator, which in turn applies voltage to the gate of a FET. The FET switches current between GND and L on the laserboard (and, in turn, GND and “laser fire” on the power supply). Power is thus controlled by the PWM duty cycle since it’s rapidly turning on and off “laser fire”.

Glorious. Everything works great now, thank you for the detailed explanation!

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