CSC 416 Real-Time Systems

Lab #5

 

Goal

Find an infrared (IR) beacon in a playing field that contains 

  1. tall boxes that can block line-of-sight view of the beacon, and 
  2. short boxes that can be seen over, but must be avoided.

Find is defined as approaching to within 0.5 meter of the beacon and playing a melody of your choice to indicate that the robot has found the beacon. Your robot must clearly indicate that it believes to have found the beacon. 

Technology

When experimenting with IR diodes (emitters) and IR phototransistors (receivers), a continuously lit IR diode can only be detected to a range of a 0.5 meter with the Handy Board's 8-bit analog input channels. When distance is greater than 0.5 meter the signal from the IR diode is lost in the noise. Amplification of the detector output does not help, because amplification also amplifies the noise . 

IR remote controls for TV's over come this problem by creating an infared signal that can be distinguished  and separated (filtered) from the background noise and then amplified. The unique IR signal is created by rapidly turning the IR diode on an off at a known frequency. The receiver then uses a notch filter to isolate the signal and then amplifies the signal. Typically when around 16 consecutive cycles are detected to the detector output goes low.

The Handy Board has a  Sharp IS1U60 receiver with a center frequency of 38.0 kHz. The Handy Board has no actual IR transmitter; however, you can easily connect one by using the J7 connector to drive the transmitter. Pin 3 of J7 is connected to a 38 kHz oscillator constructed from a NAND gate, resistor  and capacitor (see Section 9.5 of Handy Board manual). The oscillator is enabled when the input to the NAND gate is high. This input is connected to Port A, Bit 2 of the 68HC11. 

IR_control.c has code to display the output on the LCD.

The single receptor on the Handy Board can be augmented with externally mounted sensors. Digi-Key sell many different IR receivers and transmitters. The PNA4611M receiver has a wide 80 degree half power angle while the LN175 transmitter has 120 degree half power angle. These seem two of the best suited detector/emitter pairs for our purposes.

Requirements

  1. Determine how many sensors you will require. Up to three extra external sensors can be used. Describe your configuration to the instructor.
  2. Create a thread that measures the signal strength from the IR beacon. Use a global variable to share the information with the other threads. Have the board beep when the signal is strong.
  3.  Submit  electronically a two page write-up describing
    1. the behaviors used,
    2. threads used, and 
    3. the contention mechanism between behaviors.
  4. Submit code electronically.
  5. Demonstrate robot to class.

Grading

A

 Locate the beacon behind multiple tall boxes with  a maze short obstacles blocking the way.

B

 Locate a beacon behind a tall box with  a maze short obstacles blocking the way.

C

 Locate a beacon in an open field  behind one tall box.

Handy Car

A frontal view of the Handy Car used in this project. The car "radar" is constructed from a  PNA461 mounted on a servo motor. The black shroud on the sensor was need to help the directional accuracy of the sensor.

On the bottom deck are the Sharp GP12D2 distance sensors.
A side view of the robot. The white proto board contains the small circuit necessary to switch between the control of the steering servo and the "radar" servo.

MPEG Videos of Final Demonstration

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