Mendel USB and power connector

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Power-usb-side.jpg

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 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.

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

XLR-connector.png

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 chocolate block and tighten its screws on just them and the short U wires in the same holes.To stop the wires flapping about you can drop them down one of the stepper-controller board holes and back up another one, as in the picture.
  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.
  7. With none of the rest of the RepRap circuitry connected (i.e. with no wires coming out of the chocolate block connected to RepRap 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

Usb-cable.jpg

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.

You will need an FT232RL UM232R USB to Serial UART Development Module from Future Technology Devices International Ltd. (alternatively, see the bottom of this page for a simpler, though less neat, alternative). This 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.

  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.
    Usb-pcb-connections.jpgUsb-wire.jpg
  2. Cut an 800 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 right to the stripboard. 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.
  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.
  4. Usb-fitted.jpg
    Attach the stripboard to the top of the power and USB cable assembly with two M4 nuts and two washers on the top. Don't put washers underneath - they may short tracks.
  5. Motherboard-connections.jpg
    Using cable ties run the ribbon cable up the angled support of your RepRap machine, over the reprapped angle bracket at the top and onto the left side of the board that holds the Motherboard and the extruder controller(s). Use a final cable tie to attach it to that board next to the Motherboard. The 6-way connector is the one labeled A. The green (RTS) side of the cable goes to the top, and the black (GND) side goes to the bottom.




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...