IR Sensor

I have come across many IR transmitter and reciever circuits over the internet. They happen to be of a very wide range from a single transistor transmitter to transmitters that will look reali high funda to newbies.The first time i searched for my first circuit for IR sensor i had a tough time. My friend gave me a circuit with a 55 timer and aTSOP to recieve.This is the most popular form of IR sensors used at college level robotics. Here in the city(Chennai) there is a place calle Ritchie street. People over there rig up circuits for you and if you can make their pockets heavy the can just do anything from a LED display to amicrocontroller Kit. now the frist time i go there with my poor 555 timer circuit for IR sensor and esk him to wire it up. I got a blank reply “This circuit will not wotk and do you want to buy my circuit for 600 bucks??? it will work properly!1″… This was pretty much an interesting start for a ‘new to robotics’ (then!!) guy like me. so here is one circuit that is so straight forward that you can hardly question its proper functioning.

A normal led looks like in the picture

Now follow the circuit.The circuit is as below

Description

FOr thoe who are new well it is like this. The Ir led is just forward biased diode and the reciever is a normal led like looking reciever. In my place i get it if i ask for just “IR reciever”(That looks more or less like a normal LED) .Well the reciever is reverse biased thus the input to PIN 13 of the 7414IC remains “HIGH” thus the output (PIN12) being inverted will be “LOW“. Thus the LED will not golw.

When the reciever recieves IR waves from transmitter the reciever will be forward biased and that will literally ground the supply(not really though). so input to pin13 gets”LOW” and sice the IC is inverting typethe output is “HIGH” and the Led glows.

CRUX

1)At the point above reciever the voltage remains about 2.25v when no IR is recieved thus IC output is low

2)When IR is recieved the volatage just above the point above reciever the voltage goes to 0.23V and thus the IC inverts it and shows up a HIGH and thus the indicator LED in series with the 100 ohms glows only when it recieves IR.

PRECAUTIONS

The other circuit with 555 timer can be asjusted for sunlight and interference .This circuit above will be affected but doin what i say now will help a lot and it has workled satisfactorily in alll conditions for me. just wrap a black tape around both reciever and transmitter and streamline your wave path.This removes most of the interference.

APPLICATIONS

1)This can be used to find obstacles which can be done by makin the IR led and reciever LED facce in the same direction places close to each other.Tracing a white path can also be done this way.
Note:This can be literally put to any use . like i made a fuel flow meter with this concept!!!(water flow cuts the IR when it folws between transmitter and reciever!!)

—Madan