How to save $20 on the Motherboard

You don't need to buy the $20US USB to Serial cable, provided you have a Arduino sitting around. You san solder some wire from the serial header to the TX, RX and GND pins on an Arduino. (See the picture below.) Power the boards independently (not shown in picture.)

The serial header only has 5 connections GND, GND, TX, RX, and RST#. If you examine the RepRap motherboard's schematic you will see that RST# goes nowhere. (It's the same story on the Arduino.) So you only need one GND, TX, and RX. Yes, GND is important.



On the Arduino board is a derivative of the RS232 a chip which converts from USB to serial levels. This is built into the $20 USB to serial cable, which makes sense if you are programming lots of controllers, then you only have to purchase one chip. However if you only program one controller is makes sense to put this on the board, like the Arduino did. I see both sides to the argument. If you look at the cost of the two options you will need to personally have 10 to 15 controllers to justify the investment in the $20 cable. I don't have that many.

Wow, I wish I had known that before I bought a USB to serial cable :-(

Im guessing the same trick will work with a Sanguino?

Phil

I saw mentioned somewhere about using an arduino as a USB to serial adapter for programming, glad to see someone tried it! I was hoping to avoid buying a $20 cable when I eventually move to the RepRap motherboard, and it looks like i can!

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This would not work if you only had a Sanguino. There is a bad-ass chip on the Arduino called the FT232RL, the Sanguino does not have this.
The chip is kind of expensive $4-5US, it may be possible to do this with a cheaper chip like the MAX232 but I have yet to do it.

It would be nice to go with a microcontroller that has built-in USB; it would save people money. The AT90USB646 would work for that, it has 6PWM outputs, all the memory of the Sanguino, and is cheaper!
If someone wanted to make their own *uino project I think this would be a noble cause.

The 18F4550 sure has intrinsic USB and a lot of power besides. I've been happily using it for several years now. :-)

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