Mendel USB and power connector

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This page describes how to get power and USB from your computer into your RepRap Version II "Mendel".

The RepRap Power Supply

RepRap needs as 12 volt power supply capable of supplying at least 5 amps. You can either buy a power brick with that specification, which will be expensive but neat, or you can hack an old PC power supply, which will be cheap but slightly scruffy. You can also run RepRap off a 12 volt car battery, or the 12 volt power socket on a car dashboard.

RepRap's USB and power connectors are stacked one above the other on the left at the back of the machine. There's a close-up view on the right. The two connectors are mounted on the panel that also holds the stepper driver boards.

The standard RepRap 12v power connector is a 3-pin XLR connector.


The picture immediately above is looking into the socket (female) and at the pins (male). Pin 1 is the ground (negative) connection and pin 2 is +12v connection. Pin 3 is not used. Mendel has a panel-mounted male connector. The two wires from the power supply end in a female plug that will plug into this.

  1. Attach four 'chocolate block' screw connectors to the M8 threaded rod just behind the Z-axis stepper motor using cable ties. Two of these will be ground, and two will be + 12 volts. You can see these in the picture at the top of this page at the top right.
  2. Xlr-power-mendel-plug.jpg
    Solder two different-coloured wires 120 mm long to pins 1 and 2 on the back of the panel-mounted male connector. Make these, and all the rest of the 12 volt power wires in your RepRap, reasonably thick - they have to carry a few amps. Wires intended for mains wiring are fine. Tin the free ends.
  3. Xlr-power-fitted.jpg
    Put the connector in the inverted-U reprapped holder and attach them both to the board with two 35 mm M4 screws, four washers and two nuts. Put the screw heads at the bottom, as in the photograph.
  4. Cut, bare, and tin two short lengths of the wires you used. Make these into a rough U shape and use them to connect adjacent pairs of the screw terminal block. Don't tighten the screws in that block yet.
  5. Run the wires from the panel-mounted male connector to the panel-mounted male connector and tighten its screws on just them and the short U wires in the same holes.
  6. Power-brick.jpg
    Wire up the XLR socket to your power supply. The picture shows a 100W 12v power brick, but an old PC supply will work just as well. For a PC supply, the +12v wires are yellow, and ground ones are black.
    • With none of the rest of the RepRap circuitry connected* (i.e. with no wires coming out of the chocolate block connected to circuit boards) connect your power supply to the mains, switch it on, and use a multimeter to check that you are getting +12v and ground on the chocolate block where you expect it.

The RepRap USB Connection

You'll also need a USB to TTL converter so your computer can drive your Mendel via one of its USB ports.

Alternatively it is possible simply to buy a USB to TTL cable here. This will simplify your initial wiring up slightly, but it will mean that your Mendel will have a trailing lead. If you put a USB socket in the machine and wire it up as above, you will be able to unplug your machine completely and carry it around easily. You will be surprised how useful and convenient it is to be able to do that...