Abstract:
This paper describes a system for pedestrian detection in infrared sensors. A specific stabilization procedure is applied after data acquisition and before processing to cope with vehicle movements affecting the sensor calibration. The localization of pedestrians is based on the search for warm symmetrical objects with specific size and aspect ratio. A set of filters is used to reduce false detections. The final validation process relies sensors data on the human shape’s morphological characteristics.
The Parts
The two basic parts for working with IR are the emitter and the detector. The emitter is typically an LED that emits near-infrared light. A typical wavelength is 880nm, which is just beyond the human eyes ability to see. Many suppliers, new and surplus, can provide you with sources of LED emitters. A typical IR detection system will use two emitters. By controlling when the emitters are active, the detection system can determine simple directional information: Left, Right, or Front.
The other important detector for working with IR is a detector module, such as the Sharp GP1U5 (also the G1U52X) module. This module contains the IR detector and a small circuit that detects a 40khz modulation (i.e. the IR light is flashing on and off at about 40khz). The nice part about using a modulated light is the ability to reject noisy light signals. The world is full of light sources. Being able to detect a certain quality of a light, such as flashing at 40khz, means you can filter out much of the light you don’t want.
Fig: The components of IR Detection System
The above photo shows these parts installed on the front of a robot. The Sharp IR detector module is the square box at the top of the frame, and the emitters are enclosed in aluminum tubes near the bottom.
The Schematic
To use the Sharp IR detection module, you need to have a circuit that can flash the light at 40khz, which is 40,000 a second (pretty fast!). This is called modulation. The circuit that does modulation is called an oscillator, and as shown one below.
Fig : A simple 40khz modulation circuit.
The above circuit is an interesting one to look at. It uses a single 74HC04 (inverter) in several ways that you don’t normally see, especially all at once. Lets take a quick tour.
There are three major parts to the circuit. The center (U1:A and U1:B plus discrete components) forms a feedback oscillator. If you follow the flow of the logic gates, you see that the output of A is fed into the input of B, which is fed to the input of A. Now, there is a gate propagation delay factor that causes this circuit to continuously flip states. The important state is the output of gate U1:B, which is fed to the driver gates. The resistors and capacitor in the circuit are there to regulate the frequency at which this circuit feeds back into itself. Resistor R2 can be used to adjust the frequency of this circuit. The Sharp detector is fairly forgiving about the exact modulation frequency, but getting it as close as possible to 40khz is recommended. Note that the above circuit is tuned to work with the 74HC04, and is known NOT TO WORK with the 7404, 74LS04, and other TTL versions. Do yourself a favor and get the real thing.
The output from the oscillator is sent through two buffers. Here the gates act to isolate the oscillator section from the IR emitter section. The buffers also act as current sources for the IR emitters. It is important to isolate the oscillator from the LED’s, since the timing would be affected by the particular types of LED you use.
The final gates are the U1:C and U1:D gates. These are the control lines that you would connect to the output ports of the CPU. They act to buffer the CPU from the current requirements of the LED’s.
The interface to the CPU is done through pins 5 and 9 in the above circuit (gates C and D). These control when the emitters turn on. The only other variable is the resistor R2, which should only require initial adjustment to get the correct frequency.
The Detector module is simple to wire up. The connections are to power, ground, and the output signal. The output from the sharp detector is a digital signal.
Notice that R5 acts as a pull-up resistor, similar to other digital inputs. Capacitor C1 acts as a bypass capacitor. Another unusual connection is between ground and the case. Most of the Sharp modules are intended to be mounted on a circuit board. It expects the case to be grounded. Be sure to make a electrical connection between ground and the case by soldering a wire directly to the metal housing.
Components used:
8051 Microcontroller:
The 8051 architecture provides many functions (CPU, RAM, ROM, I/O, interrupt logic, timer, etc.) in a single package
- 8-bit ALU, Accumulator and 8-bit Registers; hence it is an 8-bit microcontroller
- 8-bit data bus – It can access 8 bits of data in one operation
- 16-bit address bus – It can access 216 memory locations – 64 KB (65536 locations) each of RAM and ROM
- On-chip RAM – 128 bytes (data memory)
- On-chip ROM – 4 Kbyte (program memory)
- Four byte bi-directional input/output port
- UART (serial port)
- Two 16-bit Counter/timers
- Two-level interrupt priority
- Power saving mode (on some derivatives)
Programming Language: Embedded C
Sensors: Passive IR Sensors by Sharp.
Robotic car:
DC Motors: Bi-Directional
Motor drive: ULN2803
Buzzer
LCD: JHD 162A
Output: Display status on LCD. If obstacle found raise alarm on Buzzer.
Algorithm:
Step 1: Initialize system, check sensors,
Step2: Read data from sensors
Step3: Analyze data received from sensors.
Step4: If a moving object spotted find approximate speed of the object. Else go to previous step.
Step5: Intimate user by Buzzer Alarm and Display Alert on LCD.
Step6: Go to step 2.