Saturday, August 11, 2007


Looking forward

I've been trying to get one of my sample pic chips (18f2550) working using usb. Finally got it recognized and the driver installed. Amazing how many ways there are to wire so few pins. But in the course of my investigations I found some things that may be relevant to where the development team has stated where they want to go. There is a nice little USB to i2c project with linux/windows/mac support at

Seems a simple enough project to provide i2c directly to our devices. There are lots of i2c software out there that would have to be incorporated into whatever device is used for the controller. The other piece is jUSB which would provide the interface between Java and our i2c bus. There are linux and windows components for that referenced at

Of course we could always just talk to our devices directly via usb, but having the i2c access would maybe be the more direct way of doing it. The controllers could still be usb programmable of course to facilitate updating. I like the booting via usb concept which eliminates needing a programmer except to get initial code into chips. But with something like rrrf and a base of reprappers that might eliminate the need for programmers except for those that want to do it themselves. I actually have to do it, but since I have a jdm programmer that works, I just added icsp to it and put connector on it and test circuit. Hopefully I can get to writing some actual software and download it now that I have the circuit recognized :)

Give me your thoughts, cheers and jeers. Happy reprapping :)

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I am SO glad that you took on this task, Bart! I was just gritting my teeth and looking at the microchip lists of 18F chips a few days ago.
I agree PICs are the way to go -- I don't think we'll find any other reasonably-priced USB chip that's not surface mount. Speaking USB to every controller is too cumbersome, so I think you're on the right track with the USB to I2C route.

I played around with a sort of interim step a while ago, where the powercomms board basically acted as a USB to serial converter that spoke SNAP, using a 18F2450. It has been working really well so far, but I'm still a ways from printing, and I know it won't fail until there's something tangible it can break in the process :-)
My machine uses I2C. The only downside I can see, apart from obviously needing two wires instead of one, it that you can't debug it with a terminal emulator, you need a digital scope or a logic analyser.
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