The Pulse Width Modulation signal (PWM) can be configured in terms of polarity and frequency and connects to the PWM input on laser drivers, which is typically labelled ‘IN’. The PWM is often used in combination with the Laser On aka ‘LO’ signal.

There are two connection points to the PWM signal. Electrically they are identical, but slightly differing mechanical specifications allows the user to select the point that physically connects best.

PWM polarity

$ settings are used to define the polarity of the PWM signal.

$98 = 0 default standard polarity setting for the K40 and most CO2 lasers, ie. logic HIGH outputs 5V to activate the laser fully

$98 = 1 inverted polarity setting, ie. Logic HIGH outputs 0V to activate the laser fully

Laser diode driver application

Some diode lasers require an enable (TTL) signal as an input to the diode driver. Typically you would need to set $98=1 and $99=1 to set Laser On output to 5V to activate the laser.

PWM Frequency

The PWM frequency is configured via the table below. For most applications 1.5kHz seems to work well. Laser diodes can use higher frequencies like 10-15kHz.

$28 settingFrequency
060 Hz
41 kHz
51.5 kHz (default)
$28 Frequency configuration

Hardware instructions

The PWM output is pin 1 of the keyed JST connector J1 in the corner of the board.

MG3 PWM output pin locations

The connector is a 4 pin JST 0.100″ pitch connector (see big markup rectangle). Alternatively, you can use the JP3 pin header on the board (see small markup rectangle). PWM levels are referenced against any pins labelled GND on the hot side of the board. The ground pin on the large four pin power connector (MTA156) is a typical GND reference.

Make sure the PWM wiring is neat and tidy and is positioned away from the high voltage leads of the CO2 laser power suppy. Ideally you should use a shielded wire.

The MG3 controller’s PWM signal can drive 150mA of current @ 5 V DC which should be more than enough for with a K40 power supply or a laser diode system.