Pwm with pot wiring

Homebuilt machine with cohesion3d mini and smoothie firmware

I’m unclear on how I would wire my lpsu to the card to use pwm in conjunction with a pot to limit current? I understand how to wire a pot for manual control and how to use pwm without a pot, but combining the two has escaped me.

A pot would get hooked up to Gnd IN 5v on the LPSU to set the power maximum. The C3D board would get hooked up to L and Gnd on the LPSU to send PWM to the laser. The power is the % power in software of what you have set on the pot as the maximum.

So what pin on the c3d would get wired to L?

For the C3D Mini, the green indicates where L should get plugged in:


Ok, Makes sense. Thanks!

so is this method an appropriate way to run a 130 watt tube? i.e. is it possible to damage my tube using it configured like this? I set my max power to .8 in the config.txt so it seems unlikely I would overpower it.

Do you have a mA meter installed on your machine? If not, you should get one, as the only way to tell if you are over driving the tube is to know what mA of current is being sent to the tube.

Yes, I have a ammeter installed. I guess the part i am unclear on is if it will pulse at full power? I understand that as the pulse widens it will be at full power for longer, or maybe I am misunderstanding the mechanism here.

The pulse duration increases as you raise the power. But effectively what you are doing with PWM is modulating a 5V signal that goes to the LPSU. If you send a signal at 100% power it will effectively be 5V, causing the LPSU to output it’s maximum current. At 50% PWM, it would be 2.5V sending 1/2 the maximum current level. So what you need to determine is what the maximum current your tube is capable of and stay at or below it. (130W tubes generally can handle 28mA of current without it hurting the tube, but best to find out what the specs are on your tube) Since you have capped it at 80% in the Smoothie config, I doubt you will be getting to that maximum value.

so I upgraded my board to a laserboard. I cant find a diagram with the pin numbers on it, unfortunately. is pin 2.5

going to be the negative pin on the connector I circled? My config should be as follows, correct?

Laser module configuration

laser_module_enable true # Whether to activate the laser module at all. All configuration is
# ignored if false.
laser_module_pin 2.5 # this pin will be PWMed to control the laser. Only P2.0 - P2.5, P1.18, P1.20, P1.21, P1.23, P1.24, P1.26, P3.25, P3.26
# can be used since laser requires hardware PWM
laser_module_maximum_power 0.8 # this is the maximum duty cycle that will be applied to the laser
laser_module_minimum_power 0.0 # This is a value just below the minimum duty cycle that keeps the laser
# active without actually burning.
#laser_module_default_power 0.8 # This is the default laser power that will be used for cuts if a power has not been specified. The value is a scale between
# the maximum and minimum power levels specified above
laser_module_pwm_period 200 # this sets the pwm frequency as the period in microseconds

switch.laserfire.enable true
switch.laserfire.output_pin 2.5!^

You do not need to make any changes to the LaserBoard config file. You do need to use the files that came with the LaserBoard for it, as they are different than anything that came with the Mini.

Connect L and Gnd to Laser Fire and Laser Gnd as marked here:


The white plug and the screw terminal are the same electrical connections.

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