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".

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 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 neat, or you can hack an old PC power supply, which will be very 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.

The standard RepRap 12v power connector is a 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 plug connector. The two wires from the power supply end in a female socket that this will plug into.

Wire up the XLR female 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.

The RepRap USB Connection


You'll also need a USB to TTL converter so your computer can drive your RepRap via one of its USB ports. The picture shows the converter wired up and ready to be attached to the RepRap machine. Do this attachment as the very last part of putting your RepRap machine together. You can use this cable loose for testing and set-up; indeed, it's much easier to test and set up the machine with this cable unattached.

You will need an FT232RL UM232R USB to Serial UART Development Module. You can order it from Future Technology Devices International Ltd., Digi-Key, or from MOUSER Electronics (alternatively, see the bottom of this page for a simpler, though less neat, alternative). The FT232RL UM232R is the green PCB that you can see in the picture. It handles all the transactions between the USB bus and the computer, and gives you a simple serial interface at the back-end that you can connect directly to the RepRap Motherboard that is controlling your RepRap machine. For those based in the USA, Sparkfun has some small boards at a good price.Sparkfun Boards

  1. Usb-underside.jpg
    Start by cutting a 40mm x 45mm rectangular piece of 2.54mm-pitch stripboard. Drill two 4mm holes 30mm apart at one end as shown, and two 3mm holes near one edge 12 mm apart again as shown (with the blue cable tie). Cut all the tracks down the middle as in the photograph, and the 5th track in on the 4mm hole end, also as shown (these last are to prevent the 4mm nuts shorting out the FT232RL UM232R). Solder the FT232RL UM232R to the stripboard, with its USB 'B' connector at the end with the 4mm holes. The end of the connector should be just flush with the edge of the stripboard.
  2. Cut an 700 mm length of 6-way ribbon cable, split off the six wires at one end to a length of about 25mm, bare them, and tin them. Solder the wires in the sequence shown on the diagram of the wire. The connections correspond to the red dots on the left view. Use a thin cable tie to attach the ribbon cable to the stripboard via the smaller holes. Leave a small loop free to give strain relief. Jumper J1 should connect pins 1 and 2, and jumper J2 should be present. (The picture shows J1 connecting pins 2 and 3, but that's just the default picture from the datasheet - connect pins 1 and 2).
  3. Attach a 6-way 2.54mm-pitch header to the other end of the cable. Colour the RTS end of the header green with a felt-tipped pen, and the GND end black.

Alternatively it is possible simply to buy a USB to TTL cable here that will plug right into the Motherboard and give you a USB 'A' connector at the other end. 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...

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