The goals of the first version electronics is to have simple enough board for home etching and to test all ideas and components I had. Also this was my first SMD project so I didn't dare to compress everything too small. The smallest things are in 0603 package.
The board uses atmega88 MCU with 12Mhz resonator. It has in circuit programming connector but unfortunately no debug/UART connector. It uses LDO 3.0V regulator in SOT23-5 package. I chose 3.0V because all components work on so low voltages and lipo battery gets to 3.2V when almost empty. There is MAX1555 IC for charging. It charges with maximum current of 200mA, so fully charging takes about 2.5 hours. Input voltage must be between 5 and 6V. It features charge contacts so no help is needed for charging. Also there is a voltage divider so the MCU can measure voltage in battery and go to charging at the right time. For output it has two LEDs: one green, the other one - red. Also there is plugs for servos and battery.
It has four infrared LEDs controlled by one mosfet. LEDs are for communication and distance measurement. They are rated about 1.2V and 50mA, but I use them at 1.5V. Next to every LED there is a phototransistor. Every phototransistor is connected to different ADC port and they can be used for ambient light detection, distance measurement, communication and angle measurement. On top of everything there is a 38kHz modulated IR receiver. I plan to use it for remote controlling, beacon finding and also to test how possible is to use it for distance measurement. Finally there are two whiskers in the back, they enable the robot to sense if it is on conducting surface like metal.
- Etching from factory - 5€
- atmega88 - 3€
- resonator - 0.7€
- MAX1555 - 3€
- 4X ir LED - 0.2€
- 3.0V voltage regulator - 0.2€
- phototransistors - 0.8€
- mosfet, leds, resistors, capacitors - 1€
- Total: 14€
The schematic and the board can be downloaded from here. Its a tar archive with eagle files in it.