Problem getting a laser to work

appjaws

I bought it on ebay and the supplier has no information.
I could take some photos of the board but I will need to dismantle my setup first.
I wonder what size of resistor I could connect in series to reduce the actual voltage reaching the control board

resam

Me, and others here on the forum use the HEATER_3 pin with a few extra components, instead of the fan output. Somebody even made a custom PCB for it.

https://duet3d.dozuki.com/Wiki/Laser_PWM_control

appjaws

I did start with that plan but could not get my lashup to work. I now have a better understanding so perhaps I'll try heater 3 again.
Thanks for your help.

appjaws

I still haven't got the heater 3 solution as explained in the article "Controlling a PWM Laser with the Duet Board" The diagram indicates that the expansion header pin 8 is heater 3 but I have a constant 3.29 volts between that and pin 2 which is grd.
So I am wondering if the old version 6 boards, which I am using, have the same pin assignments as the version 2 boards.

So I have reverted to using the fan connector with the output reversed and a pull-up 1K resistor connected to +5V.
This is the results of checking the voltage at different S values.
Svalue Voltage Laser
0 4.4
10 2.58
11 2.47
13 2.33 ON
15 2.27
20 2.19
40 2.05
60 1.97
80 1.88
100 1.77
120 1.64
140 1.51
160 1.39
180 1.27
200 1.14
220 1.08
240 0.87
250 0.78
252 0.77
254 0.75
255 0.74 OFF

The increasing S values at the top end result in the power of the laser reducing.
Clearly I have something wrong but I am at a loss as to what to do next.