Power supply board
W.Bot is battery powered. It uses 8 x 1.2V NiMH AA batteries (HR6).
The power board outputs 2 different voltages: 5V, used by logic circuits, and 7.4V used by motors. Voltages and current consumptions are monitored, and informations about the power status can be obtained via the I2C bus.
The power board also controls the battery recharge process: the power station can provide two different recharge currents: 240mA for the fast recharge (when the battery level is low), and 45mA for the trickle charging. The recharging currenct is selected by the power board, and the effective recharging current is also monitored.
W.Bot could be in 4 different power statuses:
- Battery powered: the status led has two fast flashes, and then a long pause
- Connected to the power station, not charging: the status led has slow speed blinks
- Connected to the power station, low current charging: the status led has medium speed blinks
- Connected to the power station, not charging: the status led blink has fast speed blinks
When W.Bot is conneted to the power station, the robot is powered via the external source, and battery is disconnected from the robot. If recharge is required, the charging current will flow from the power station to the battery.
Low or high charging current is selected by the power board sending a different signal to the power station. The power station sends a feedback to the power board about the effective charging current.
Battery charge process
If the battery voltage drops below 10.5V the high current charging is selected, otherwise the low current is selected.
If the high charging current is active, the charging process is suspended every 10 minutes to check the battery voltage: when the battery is full, the low current is selected.
The battery full event is identified when the battery voltage reach a peak, and then decreases a bit.
Charging current is selected sending to the power station a different signal via the RA5 pin:
- No current: 0Hz signal (logic level 0)
- Low current: 1,500Hz signal
- High current: 3,000Hz signal
The effective charging current is monitored reading the signal on the RA3 pin: the current is calculated measurng the high level of the square signal sent by the power station, where 1ms is equal to 1mA. So, if for example the length of the high level is 250ms, it means the charging current is 250mA.
PIC I/O Pins
|Port||Pin number||Analog channel||Direction||Description|
|RA0||13||AN0||In||Current on 7.4V power supply line|
|RA1||12||AN1||In||Current on 5V power supply line|
|RA2||11||AN2||In||Voltage on 7.4V power supply line|
|RA3||4||-||In||Charging current monitor|
|RA4||3||AN3||In||Current on battery|
|RA5||2||-||Out||Charging current selector|
|RC2||8||AN6||In||Voltage on 5V power supply line|
|RC3||7||AN7||In||Voltage on battery|
|RC4||6||-||Out||Charging status LED|
|RC5||5||-||Out||External power detection|