While experimenting Atmel’s 8-pin AVR processors ICs (specifically ATTiny85 and ATTiny13) I decided to create the equivalent of a ‘Sensor Shield’ that allows me to re-use my prototyping boards and easily program the ICs through an ICSP header.
The 8-pin Atmel ATTiny processors (ATTiny 13, 25, 45, 85) have very few I/O available (each package only has eight pins – 6 I/O + 2 power) and a relatively small amount of Flash memory, EEPROM and RAM. They all share a similar functional pinout. For this project it means that a single board design can be used for the whole family.
To make effective use of my prototyping system (described here), the ATTiny sensor breakout board needs to organise the I/O into a bank of 6 SVG (Signal-Voltage-Ground) connector pins.
As with all the other Atmel AVR processors, each of these pins also has a separate function used to program the device immediately following a reset – basically an SPI interface (MOSI, MISO and SCK) with power (+5V, ground) and a Reset. These pins are grouped into a standard 6 pin ICSP header on most Arduino Boards and the idea is to replicate that layout.
To keep the board simple the circuit does not include any power supply buffer ICs or reset circuitry, just the connectors and the processor I/O and power.
After designing a PCB using Eagle CAD, I decided to manually build two boards (ATTiny85 and ATTiny13) with available parts. The CAD layout was a useful guide when I simplified the layout to construct it as a one-sided prototype board with hand-soldered wire connections.
These small boards have allowed me to easily reuse my tried-and-tested prototyping blocks before committing to a final hardware arrangement and design.