AndyUK's Build - 1.2x1.0m Gantry

[Kitwn]

Optocouplers work a little like elctromechanical relays: When you apply a voltage across the input terminals the output terminals are connected together. In practice most couplers contain a LED which lights up to turn on an open collector transistor. The most common circuit implementation connects the LED cathode and the emitter of the transistor to ground. Your external circuit will normally include a pull-up resistor between the open collector and the positive supply so the output voltage (the collector of the transistor) is high until pulled low by a positive voltage applied to the anode of the LED. The device therefore acts as an inverter in this configuration.

There is no reason why the collector of the transistor cannot be connected to the positive supply and a pull-DOWN resistor connected between the emmiter and ground. The output is now the emitter and the circuit is non-inverting. As long as the collector is allways positive with respect to the emitter the device will work.

Simillarly the anode of the LED can be connected to the positive rail and the cathode pulled low to turn it on if that suits your circuit voltages.

All clear as mud?



The stepper controllers I have used have all deaulted to 'enabled' if the enable input is left unconnected. You could test the rest of the beast's function this way.

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