Creating an external duty control and indicator
In some projects you may wish to operate the duty control remotely so that the Power Pulse Modulator can be mounted away from the user. For example, in electrolysis or high voltage projects you may want to place the PWM circuit quite close to the load it is driving to reduce losses in long power cables.
By adding a few resistors and an LED to a length of cable, it is possible to adjust the duty output remotely. The optional LED lights up proportionally to the duty output of the circuit. You can connect the indicator LED from V+ to L- with a 1k resistor (or whatever suits your supply voltage) in series. If your load is inductive, then you should also place a diode such as a 1n4007 in series.
R1 and R2 are standard 3.9k resistors and R3 is a 10k linear potentiometer. Not shown on this diagram are the usual connections to the power supply and load which should be connected normally as shown in the product manual.
You can also leave the jumper link in place on the PWM header as this will allow you to use the onboard duty contol as a duty offset control. This allows you to force a minimum or maximum duty output. This can be useful if for example you want to prevent the duty going over 90%. With the onboard duty control set to the middle position, the external control will give you a full zero to 100% duty adjustment.