LCheapo to Open Drain PWM Wiring

Controllers Smoothie
1

I have an Azteeg X5 v1.1 and a 8 Watt LCheapo Diode laser with PWM.

I used an oscilloscope and found pin 3.25 configured as open drain will produce a 5 v pwm signal when the scope + is connected to an unused end stop ground terminal and the scope - is connected to pin 3.25. I tested this with the latest firmware and using Pronterface command of @fire 90. I also used @fire 50 and saw the pulse change according. I did not have the laser wired in at all, I just wanted to verify the board could produce the correct signal.

Now when wiring in the laser I land the power wires from the laser on the 12VDC power supply and the connection from the end stop ground to the PWM wire of the laser. Where do I land the pin 3.25 connection? I guess I should say which ground, I tried the 12vdc common but that did not work and I hate just plugging into random pins.

What am I missing.

Thank you

Imported from wikidot

2

Your driver’s PWM input must have two pins : 

  • A 5V input probably labelled “PWM”
  • And a GND for that input

As you are using open-drain, you connect :

  • Pin 3.25 to the driver’s ground
  • A 5V from the smoothieboard to the driver’s PWM input

This way you are essentially switching on the GND part of the circuit instead of what people do traditionally where they switch on the 5V side of the circuit.

3

I will have to look on the driver board for the ground connection, there were only 3 wires coming from the board. I knew the ground needed to go somewhere and back onto the smoothieboard did not compute in my mind.

Thank you and when i am back home i will take a look at the laser driver board for the pwm ground pin.