FroboMind Robot:Frobit:Electronics
Power supply
Motor controller
The motor controller typically used for the Frobit is a dual H-bridge module based on the L298N chip. The Dual H-bridge is available from China at ebay and typcially cost about $4.
Serial communication
EXT port to Bluesmirf bluetooth module
Signal Port TX-O 10 RX-I 12 VCC 1 GND 11
EXT port to FTDI cable
Signal Port TX 10 RX 12 GND 11
Motor control
Dual H-bridge connections
Signal Port Color Motor left EN PD6 Motor left C PD3 Motor left D PB5 Motor right EN PD5 Motor right C PB3 Motor right D PB2
Encoder feedback
Motor connections
Signal Port Color Encoder left A PB4 Blue Encoder left B PB1 Purple Encoder right A PC4 Blue Encoder right B PC5 Purple
Voltage measurement
The RoboCard continuously measures the voltage of the Frobit battery. The measurement is outputted through the Frobit Status message. The measurement circuit is a voltage divider between the Frobit Battery and GND, and the voltage divider output is measured using ADC0. The value transmitted is the raw output from the ADC to allow external calibration of the voltage divider measurements. The value range is [0;1023] corresponding to 0-5V on the voltage divider output.
To protect the RoboCard ADC from overvoltage a 4.7V zener diode is inserted in parallel with the smaller resistor. This ruins the linearity of the voltage divider as the zener diode has a leak current that increases the closer the voltage gets to the nominal rating of the diode. Therefore to convert the ADC output to a proper voltage, a 2. degree polynomium fitted to the output values is needed. For more information on this please see this documentation.
