Holiday and MozCamp have delayed the project a little, and I’m a touch behind on the blogging…
Every RepRap needs power and control. There are various electronics packages available for running a RepRap, designed by different people and optimized for different things. The electronics package I have is a RAMPS v1.4, bought ready-built off eBay from China. (In order to finish this project in 2012, I decided not to solder it myself from scratch…) Amazingly, it arrived before several parts sourced at the same time from the UK! It’s based on an Arduino, with a shield to contain the specialist electronics for running the motors etc. This means that it uses standard Arduino tools, and I can probably learn how to hack the firmware without too much trouble.
The PSU is a standard modern ATX PC PSU, modded as explained on the RepRap wiki. It turns out that PC power supplies are required, presumably for legacy reasons, to provide 3.3V, 5V, -12V and +12V power and, on some, -5V as well. Fortunately, all the wire colours are standardized. RAMPS just needs 12V.
The Mendel90 design had holes for a different electronics package and also had no mounting holes for the PSU, because they aren’t standard. So I had to plan and drill all these holes myself. I ended up mounting the PSU below, and the electronics above – with the power input cord and on switch on the bottom side, but the power wires coming out near the electronics. I needed to leave room at one end of the electronics to add the optional SD card reader without it sticking out in a way that means it could get knocked or damaged.
You can see from this internal view of the PSU that I have:
- Added a power resistor (bolted to fan holes, lower left) to the 5V bus (red) to create a small load (some PSUs won’t start without it)
- Wired the brown 3.3V sense wire to the 3.3V bus (orange; lower right)
- Cut away most of the remaining wires (top right, behind the yellow and black ones; a standard PC power supply seems to have 40-50 wires coming out of it with various connectors)
- Left behind 3 12V wires (yellow), 2 on one of the 12V buses (for the heated bed) and one on the other (for everything else), plus matching ground wires
- The green wire is apparently some auto-on switch; it has to be connected to ground. Until I figure that out, I kept it full length and wired it into a ground terminal