This semester, I’ve been fortunate enough to take Neil Gershenfeld’s How to Make (Almost) Anything. For one of the first assignments, we’ve been tasked with fabbing (routing on the modella and stuffing) Neil’s FabISP which is based on David Mellis’s FabISP which is based on Limor’s USBTinyISP which is based on Dick Streefland’s USBTiny.
I decided I could make a few tweaks to the design, electrically and mechanically. First, I tried out my mechanical modifications before I dove too deeply into electrical modification. First , I redrew David’s schematic in EagleCAD. I replaced the USB connector with a board edge USB connector from the SparkFun library. I also replaced the crystal with one that I had on hand, which ended up being a mistake because I decided to use the one in the Fab inventory, which is smaller.
One thing to note, I use a ground pour, because I figure if I’m going to have extra copper on my board, I’d like to know what it’s connected to. As a whole, my design is smaller then both Neil’s and David’s and dispenses with the USB connector.
If you’d like to play along at home, you can grab fabbable PNGs above and you can get the design files with a simple git checkout
git clone git://git.bardagjy.com/fabisp
Since my design is electrically similar to Neil and David’s, programming is very similar. Solder the reset jumper (the one closest to the processor), power the board (using a USB port, or USB charger), program it with another programmer (make hex, make fuse, make program), unplug and desolder the jumper.
The board is a little thin, it might require a small shim (0.010″) underneath the connector to feel solid in your USB port.