Let’s start with the PIC16F1778 since it comes in a 28 pin SOIC package which is a compromise between being easy to solder and having the most pins.
90 degree female header pins are used for power, in-circuit programming and UART communication with the PIC. Male headers will be used to allow daughtercards to plug into the PIC board.
An ADP7104 voltage regulator is used to provide 3.3~V to the circuit. This means the input voltage connected to “Vin” on the header can range from ~4~V up to 44~V. This means the board will run on 3 AA/AAA batteries (minimum) or any of the thousands of 12~V wall warts I seem to have lying around.
The ADP7104 supplies 500~mA of current at 3.3~V. The current draw of the board components is:
|PIC (32~MHz int osc)||4.2|
|AT25SF321 FLASH (Programming/Erasing)||16|
|LEDS (30~mA each)||30|
The brain will have an Adesto AT25SF321 32Mb external FLASH chip for storing measurements, audio clips, etc.
A group of 4 1x8 headers are used to allow the brain board to plug into a daughter card. The headers are divided into 2 groups of 2. In each group, the headers are separated by 2.54~mm (the header pin spacing) and the centers of the two groups are separated by 32~mm.