Power Systems Overview:
The main source of power on Calculon is two 12 Volt batteries put in series for a total of 24 Volts. These batteries are the same ones that came with electronic wheel chair platform. With the current electronics and power scheme, it is possible to have a three to four hour runtime. An extra set of batteries can be used to increase this total time.
The power from the batteries is fed directly into the onboard circuitry that came with the wheel chair. Rather than opening this box to get the 24 Volts, the wires comming from the batteries were stripped, and additional wires were soldered to them, and then re-sheathed. This is where the additional electronics we added get their power from.
Power from the batteries is then fed directly into the electronics drawer on the back of Calculon. In the drawer is a power distribution block. The two addition wires, power and ground, that we added previously are connected to this block. From this point, power is spread out to the rest of the system.
To help cut power from the distribution block to the rest of the added electronics, a switch was placed on the ground wire. If this switch is not turned off, then no power can be used by the added electronics. There are two switches on the back panel of Calculon, the far right switch is the one just mentioned. It turns on power to all of our custom electronics. The other switch is connected to the wheel chairs electronics, and it cuts the wheel chair power on and off. Both switches have a green LED above them to indicate if power has been turned on or not.
From the distribution block, 24 Volts is distributed to three sources. The first is a 24 Volt DC to AC Inverter which supplies power to the notebook computer and digital camera. Next, power is given to a 24-24 V DC to DC converter. This supplies a regulated 24 Volts to our LIDAR and DGPS unit with 90% efficiency. Finally, power is given to a 24-12 V DC to DC converter. This converter supplies a regulated 12 Volt supply to our remaining electronics with 90% efficiency also.
The 12 Volts from our 24-12 V DC to DC converter is run directly to our custom printed circuit board, PCB. This board then routes power to the vehicles magnetic encoders, cooling fans, and digital compass. The board also converts the 12 Volts received to 5 Volts using a 7805 chip. This additional 5 Volt supply is currently not used by anything, but was done for possible addition of future sensors that may require it.
In addition to the 5 Volts produces through the 7805 chip, there is another independent source for 5 Volts. The custom PCB interfaces with the wheel chairs electronics, and receives a 5 Volt supply from them to power its two PIC microcontrollers. Only the PIC microcontrollers use this power source, and it is not shared with anything else.
Graphical Representation of Power Distribution: