[Duet 3 Mini 5+] 5V_EXT_IN only 0.85V
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Hi guys,
I just received my Duet 3 Mini 5+ and plugged it into my PC to to configure it before it goes into the printer.
I'm planning to control a relay to turn off the printer's PSU after a print is done. While planning out my connectors I noticed that 5V_EXT_IN did give me 0V (which is expected) so I set the jumper on 5V_SEL and 5V_EXT_IN. Now I'm getting 0.85V when measuring 5V_EXT_IN to GND. On the other hand, 5V_EXT gives me a perfect 5V.
Is my unit faulty or is this expected behavior?
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@tsndr I don't have the schematics for the Duet3 Mini, but on the Duet3 mainbord, there's a diode that prevents you from drawing power OUT the 5v_EXT_IN pin.
(Well, R187 allows a <little> bit of power to be drawn before the voltage drops.)
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@alankilian So my unit isn't faulty and I have to find another way to toggle my relay. Thanks a lot
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@tsndr Can you describe what you are trying to do and we'll probably be able to help you figure it out.
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@tsndr I believe the 5V_EXT_IN pin if you to supply 5V to the board from an external power supply. If you aren't supplying this pin with 5v, it won't be 5v!
I guess the 0.85V comes from the resistor that @alankilian mentions.
I use an external 5v supply for my Duet WiFi and have a relay on the 24V line which is controlled by the PS_ON pin. That means I can cut the power to motors and heaters without shutting down the Duet. I think this is what you want to do?
Alternatively you can use the internal 5v supply and connect a momentary switch in parallel with the relay on the 24v supply. Add M80/81 to your config. You then physically press the button supplying 24v to the board so it boots and activates the relay (so you can release the button). The Duet can then shut down the power but not restart it without you physically pressing the button
