Boat Electrical Design - Circuit Schematics
Master PIC
Master PIC
Just like its name, this PIC controls the whole game flow such as how to handle the communications in both SPI and SCI protocols.
In SPI communication mode, this PIC is the master. It tells all the PWM PICs such as the propeller drive and the turret servo what to do according to the command received from the HC. It tells Crab Indicator Servo PIC how to moves according to the information from Neptune. We also use SPI to communicate with Security Controller Interface PIC to get the RFID serial and security key.
In SCI communication mode, it handles all the information that goes in and out of an Xbee radio. It talks to the Neptune, the fleet, and our HC through this communication line.
RFID and Security Controller PICs
RFID Reading PIC and Security Controller Interface PIC
The schematic above has 3 PICs, clockwise from top right, namely the Security Controller(SC), the RFID Reader PIC and the SC Interface PIC and a RFID reader chip on the top left. The RFID Reader reads the RFID bytes through the antenna and forwards them to the RFID Reader PIC which converts the ASCII bytes to Hex and forwards them to the SC interface PIC over UART. The SC interface PIC then relays them to the SC and receives the Security key back from the SC. It raises a line on the Master PIC high when it has got the key and then the Master PIC initiates an SPI transfer with the SC interface PIC sending the RFID bytes plus the security key to the Master.
Since the Transmit lines of the RFID Reader PIC and the Security controller are tied together, they are connected using an open-collector configuration.
Crab Indicator Servo
Crab Indicator Servo
This PIC communicates with the Master PIC via 3 output lines (i.e. 3-bit number) and displays the current crab count on our boat. This PIC also handles the waterlogged LED display.
Turret Servo
Turret Servo
This PIC controls the PWM signal to our cannon turret (one PIC for each cannon). It receives the command from the Master PIC via SPI communication.
Propeller Motor
Propeller Motor
Similarly, this PIC controls the PWM to the propeller motor (one PIC for each). It also receives the command via SPI from the Master PIC.
Pump
Pump
Similar to the previous two PICs, this PIC handles the PWM signal to the our super power 1100 GPH pump.
Power Circuit
This is our handy-dandy power board. It mainly has two parts. One part handles all the power to the logic. Another handles the power to propeller motors. These fuses had already saved our lives once!
H-bridge calculations for the motors
Maxon A3027 motors salvaged from our previous projects were used for driving the propellers since these had reasonably high rpms even at low voltages.
Assuming a fresh 7.2V battery and a motor with a 1Ω armature resistance at stall,
current dissipated in the TLE-5206 (worst case) -
Rds(on) = .5Ohm*2 = 1Ohm
I = V/R = 7.2V/(1+1) = 3.6A
This is below the 5A continuous current that the TLE can support.