The Basics of building an IR Proximity Sensor
Infrared (IR) light is electromagnetic radiation with a wavelength between 0.7 and 300 micrometres, which equates to a frequency range between approximately 1 and 430 Thz.
IR wavelengths are longer than that of visible light, but shorter than that of terahertz radiation microwaves. Bright sunlight provides an irradiance of just over 1 kilowatt per square meter at sea level. Of this energy, 527 watts is infrared radiation, 445 watts is visible light, and 32 watts is ultraviolet radiation. This infers that sunlight has more IR energy than the visible light energy.
Basic Properties of IR:
An IR Transmitter transmits energy in a broadly unidirectional fashion.
An IR receiver detects radiations omnidirectionally.
Principles of light such as reflection, refraction etc. apply to IR also.
Dark coloured surfaces tend to absorb radiation (Black surfaces absorb maximum radiation).
Usage:
The above mentioned properties of IR are applied along with simple electronic circuits to detect obstacles and to sense black lines to create line following & obstacle detecting bots.
By using an an IR transeiver (Transmitter & Receiver placed parallely), we build a sensor. When any object comes in path of the IR radiation emitted from the transmitter, it is reflected back & is detected by the receiver.
Circuit:
Note: An IR transmitter needs to be in forward bias to transmit radiation
while an IR reciever needs to be in reverse bias to detect radiation.
An IR reciever gives out analog output depending upon the IR radiation detected. So a comparator is required to produce a digital signal, depending upon a fixed value of IR radiation detected. This can be achieved by using an operational amplifier in the comparator mode.
The inverting input terminal of the op-amp is connected to the junction of a reverse biased IR reciever and a low resistance. The reciever is powered through the resistor.
The non inverting input terminal of the op-amp is powered through a resistance higher than the above mentioned.
The two possible cases here are…
1)When IR is not detected, the inverting input is higher than the non inverting input, thus leading to the op amp giving a LOW as the output.
When IR is detected, the reciever starts operating in the reverse bias and the current flows through the reciever and gets grounded, making the non inverting input higher than the inverting input, thus leading the output to be HIGH.
More to continue on this….