Mendel USB and power connector
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.
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.
- 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.
- 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.
- 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.
- 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 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
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.. 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.
- 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.
- 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. 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...