PWM Convertion

DDD

How can I convert Duet's ground-switched PWM signal to a VIN-switched PWM?
I'm trying to control a PLC via a PWM converter, but when the PWM out from the Duet is connected to the converter nothing happens because expects a VIN-switched PWM signal.

I connect a PWM signal generated via Arduino and it works.

T3P3Tony

@DDD how much current does the PLC input take and at what voltage?

DDD

@T3P3Tony the PLC works form 0 - 10 V. The converter translate pwm duty cycle into voltage with 4 A max, more than enough for the low current input for the PLC

dc42

The PWM to 0-10V converters I have seen have optically isolated inputs, so they don't mind whether the input is ground referenced or not. Can you send a link to the data for the one you have?

DDD

@dc42 for this input ground is grounded and if the optocopler is isolated the converter doesn't go bellow 1V

https://www.icstation.com/mobile/voltage-converter-module-adjustable-converter-power-module-digital-analog-signal-p-12498.html

DDD

@dc42 could a pull-up resistor work?

dc42

It looks to me that the PWM converter you linked to does have an optically isolated input, although the input terminals are confusingly labelled PWM and GND. I suggest you check using a multimeter whether there is any continuity between that GND terminal and the other two. If there is none, then treat that terminal as PWM- in and connect it to your chosen FAN- output. Treat the terminal labelled PWM as PWM+ and connect it to the corresponding positive pin of the fan output. Make sure you have the jumper on that converter in the 12V position not the 5V position.

DDD

@dc42 The input is not PWM- it's grounded with the rest of the circuit. I added a 10 Kohm pull-up resistor and was able to drive the converter, altho, doesn't go under 1V.

The same setup but with a PWM generated with an Arduino, the converter goes under 1V without a problem.

After measuring Duet's PWM signal by an Arduino, the duty cycle doesn't go under 10%. I don't have an oscilloscope.

How can I make the Duet output a PWM duty cycle under 10%?

Duet 6HC 3.1.1
M950 F2 C"0.out4" Q1000

dc42

You are controlling the laser as if it is a fan (which is not the best way to do it). The M106 L parameter sets the minimum allowed PWM.