My first exposure to EAGLE, a CAD/CAM package for printed circuit boards, produced this 82×23 mm board:
It has an ATmega168 MPU, an RFM12B radio, a 3.3V regulator, and 4 identical pin headers intended to be used as simple I/O “ports”, such as sensors. There’s also an FTDI connector, a power/I2C bus, and an SPI/ISP connector for hooking up a few more SPI devices.
Each of the I/O ports can be used in different ways:
- 2 center pins: analog or digital I/O + ground
- 4 center pins: the above, plus a second digital I/O pin and 3.3V
- all 6 pins: the above, plus unregulated power and a shared interrupt pin
In many cases 4 pins will be sufficient.
I’ve ordered a couple of prototypes, just to see how they come out. I’m sure I made all sorts of silly mistakes, but hey… it’s all a learning process.