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Overview

Signal Conditioning

Output Controls

Power System

Network and Radio Interface

The RoboCar electronic hardware consists of:

There may be other on-board electronics as required for wireless links and other device specific functions.

Each RoboCar bumper will  operate a microswitch when a collision occurs. The switches will be debounced and feed Schmidt trigger buffers built into the RA binary inputs on the I/O Processor's PIC chip.

Level -- An analog voltage relative to the battery level. The raw 12 volts from the battery will feed a differential opamp input. The other differential input will be an 11v reference voltage. The range of the signal will be approximately 0-3.5 volts and will not be reliable when the battery drops below 11 volts, however it will be sufficient  to gauge the battery charge level and the need for recharging.

 
Charge -- An analog voltage relative to the current flow in and out of the battery. A low value resistor will be inserted between the battery and the rest of the system. The voltage across this resistor will feed a differential opamp which amplifies the relative current flow value. The range of the signal will be approximately 0-3.5 volts, where a voltage of approximately half (1.75v) indicates no current flow to the battery and levels above and below that will indicate charge (+) and discharge (-) rates respectively.

 
The outputs of both battery indicator opamps will feed analog inputs on the I/O Processor's PIC chip.

The Locator Signal is a serial  infrared signal  broadcast from various RoboCar devices. It is a standard PWM data stream using a 40Khz carrier. It is sensed by two separate systems, one to collect the actual data from all directions, and one to detect the strength of any Locator Signal directly in front of the robot.

 
Data -- A full circle photo-transistor array will pickup any Locator Signals which are in range. This detector will feed an opamp amplifier and then be demodulated into serial data and fed to a CCP (Capture) input on the I/O Processor's PIC chip.

 
Strength -- A narrow beam photo-transistor sensor mounted on the front of the RoboCar. The detector will feed an opamp amplifier and high-pass filter to eliminate non-Locator Signals. This signal then feeds an integrator which will produce an output voltage relative to the absolute strength of the signal in the range of 0-3.5 volts. The resulting voltage will feed an analog input on the I/O Processor's PIC chip where it will be converted into an 8 bit signal strength value.

Signal Carrier -- The 20Mhz PIC chip clock will be divided by 512 to produce the Locator Signal carrier. A PIC chip CCP (Compare) output will gate the clock to produce the RoboCar's Locator Signal data stream. This stream will feed a driver on the power card.

A Passive InfraRed sensor will be mounted on the front of the RoboCar. The output from the PIR will be amplified and cleaned up into a short duration pulse to be fed to a binary input on the I/O Processor's PIC chip.

Both the Drive and Turn controls can be used on cars that have two independent drive motors, or on cars that have a single drive motor and a separate steering motor or solenoid. The descriptions below assume the latter, however the former (2 drive motors) is a more practical mechanism for heading control. On systems with 2 drive motors the wheels can be run at different speeds and in different directions to implement steering.

The RoboCar drive is a simple DC motor. Two RB outputs from the  I/O Processor's PIC chip will feed a TTL open collector buffers who's outputs will be wire-ORed together with appropriate 12v pullup resistors. The output of this will provide 3 levels of current drive to the drive motor amplifier on the power card. When both RB output bits are off no drive current will be produced and the drive motor will be stopped.

The RoboCar steering mechanism is also a simple DC motor. Two RB outputs from the I/O Processor's Pic chip will feed a system identical to the drive motor described above. In dual motor drive configurations this system can be adapted to operate the second motor with appropriate modifications to the PIC chip programming.

The output Locator Signal is driven by a two byte serial data stream from the Main Processor. The locator data will be formatted by the I/O Processor PIC chip which will use one of its CCP Compare output pins. This output will drive a circuit that modulates a 40 kHz carrier (nominally the same technique as is used for standard IR remote control). The modulation circuit is described in the Signal Conditioning section above. The modulated signal feeds a driver on the power card which flashes a 360 degree array of IR LED's mounted on top of the RoboCar.

 

The battery monitor and charging system, voltage regulator, and the drivers for the motors and locator signal LED's will be mounted on one power circuit card in order to localize heat sinks and wiring.

The LED drive is a simple NPN darlington transistor with appropriate current limiting resistors. The motor drivers are modified H-bridges capable of supplying variable currents with either leg of their outputs being positive (in order to reverse the DC motors).

The Battery circuit contains a diode, to prevent the charging connector from shorting or being reverse-connected, and a small value resistor to act as the current detector. The level detector is a comparison between a known low battery voltage reference and the raw battery voltage. Both the current and level detector outputs are sent to opamps on the I/O Processor card for amplification and level shifting before being fed into analog inputs of the PIC chip.

The voltage regulator is a standard 5v chip with a current limiting resistor and diode to isolate the input filter capacitor from sudden fluctuations and noise in the raw supply voltage caused by motor and charging circuits.
 

TBD. Not planned for initial prototype. The Ethernet and serial ports will run the standard TINI `slush' shell and can be used for monitoring and controlling the RoboCar. The radio link will be added as time and money permit. Possible technologies are 802.11 or Bluetooth.