Adding Third Hotend Cheaply

  • I wand to add a third hotend but i dont want to buy the whole duex expansion board just for one more thermistor and heater. Is there a way i can add those components more cheaply like with a solid state relay hooked up to the heater pins on the expansion headers (to reduce the current requirements through the pins)? The thermistor is low current enough that would it be possible to plug it directly into the expansion headers? Thanks.

  • administrators

    Yes that's possible. There is a wiki page about adding external drivers. You can connect the control terminals of an SSR between +3.3V and one of the extra heater signals on the expansion bus. The signal level is 3.3V, which is enough for most commercial SSRs but might not be enough for the cheap ones on AliExpress etc. unless you reduce the value of a resistor on the SSR.

    You will need to connect a 4K7 resistor between the thermistor input and the VREF pin on the expansion bus.

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