The first prototype hardware hilariously uses two Arduino shields and no Arduino. It is a:
- Electric Imp (includes an ARM Cortex M-3 processor and wifi)
- Electric Imp Arduino shield“break out board”
- With the included cut-able traces left intact, D9 and D7 jumpered together and a 2.5mm barrel jack added into the prototyping area and connected to the +5V pin which supplies both the Imp’s 3.3V regulator and the RFID module on the other board.
- SM130 Arduino shield
- With solder jumper SJ1 set to D8 and SJ2 set to D7
By Setting up the above jumpers, the UART on the module is connected to the UART level shifter for the Electric Imp and the two devices can talk directly to each other. No Arduino is needed.
Bill of Materials
- Electric Imp – $30
- SM130 Mifare RFID module – $30
- Breakout “shield” boards – $40 – When we convert to custom boards it should be possible to get this down to more like $20
- Powerswitch Tail – $26 – For switching power to devices under control
- Equipment monitoring electronics – ?
- Enclosure – ?
Total estimated cost of a developed system, less than $150.