Infrared Obstacle Detector is useful in many applications. One of the most demanding applications can be a tool for blind person. Latest technologies like Automatic (driverless automobiles, train anti-collision, electronic toys like car, train, and robotic gadgets etc.).
The principle involved is infrared (IR) emitter and receiver. When IR emitter emits light and it becomes incident on an obstructing object, it gets reflected. This reflected light is picked up by a sensitive receiver and can be converted to suitable signal to alarm the user regarding the obstacle. Absence or reduction of received light decides the presence or absence of the obstacle.
Modulation is the answer to make our signal stand out above the noise. With modulation we make the IR light source blink in a particular frequency.
Another purpose this modulation solves is to make the circuit more sensitive and able to work with higher range i. e. to detect obstacles from more distance, the light emitter is modulated at about 38 KHz.
About the Circuit :
- The Emitter is fabricated from IR diodes D1, D2. These diodes are driven by IC2- 555, used as astable multivibrator running at about 38 KHz. The frequency can be tuned with VR1. The transistor T1 driven from 555 outputs drives two IR LEDs connected in series. Two LEDs are used to improve upon the range and sensitivity of the circuit.
- The receiver is an integrated circuit TSOP 1738. TSOP 1738 is the standard IR remote control receiver series, supporting all major transmission codes.
- It has Photo detector and preamplifier in one package. Also, it has internal filter for PCM (pulse code modulation) frequency. Its output is active low, and gives active low pulses when it receives IR signal from transmitter after reflection from the obstacle. Normally when there is no obstacle, the transmitter signal will not be received by receiver since both are arranged in parallel on the same end of a PCB. This output is connected to trigger input of IC1, which triggers when IR light is obstructed. IC1 is configured in mono-stable mode and generates a pulse of 1.1 R3xC3 time each time it is triggered. With no obstruction present, the 555 (IC1) output is LO.
- The relay is driven by the pulse produced by IC1. Simultaneously the buzzer will also sound alarm for the duration of the pulse produced and LED D4 gives visual indication. Relay contacts can be used to actuate any other mechanism to suit an application.
- By synchronizing the transmitter and receiver frequencies, we can get highest sensitivity. Since the receiver is an IC and has fixed frequency circuit in it, the VR1 is provided to match the frequency of Transmitter with that of receiver.
- Regular IC3 (7805) is provided to get regulated voltage of 5 v for IC1 and sensor to avoid the sensor going bad due to over voltage.