There are often things you want to test quickly when designing something. Most of the time you need some set of I/O pins (often more then fewer) and some quick-and-dirty debugging (i.e. serial) to get going. I was approached at the local hackerspace OSAA if it was not possible to make a few simple boards which would be cheap
, have a lot of I/O pins and a serial port via USB. The target was set at about DKK 100,- (that is Danish kroner); or about $18,-. With the price-target set, we had to choose not to go the Arduino route, as they are much more expensive.
What I came up with is the following:
There are (for avr) 32 and (for pic) 36 I/O lines available on the two 19-pin pin headers. The power can be supplied via USB or injected on the header. It includes a 3V3 regulator (as it uses 3.3V signaling) and a serial/USB converter which can be disabled/detached via 0R resistors. The CPUs used are ATMega32A and PIC18F45K22, which are powerful and have lots of functionality and memory. Both processors run on a 16MHz crystal.
Both PicStamp and AvrStamp have about the same pin-layout on the headers. Ports B/C are swapped between AVR and PIC because of the chip-layout. The pic version has some port E pins where there lack the high bits of port A and the avr has an analog ref pin. However, the boards are basically swap-able if you take these small differences into account and the TX/RX pins which are located at different ports for avr and pic.
I programmed a Blinky program to flip portA.bit0 and included serial comms as a quick test.
The schematic diagrams are available on my site at http://www.vagrearg.org/content/avrpicstamp
and some more notes on the development. The complete PCB sources will also be available when the design is stabilized (or send me a PM). The design is CC-BY-SA-3.0.
The price-target can be met for these small devices when I can produce them in volumes of 100+. Otherwise it will be about 25% more expensive. Still, not bad for the functionality.