Design of Infrared IR transmitter and receiver circuit using 555 timer and tsop1728
In order to design the complete ir circuit, we need to understand the basic fundamentals about the infrared rays and ir diodes. For transmitter ir diode can be used indium gallium arsenide to produce ir light. For ir receiver we use tsop1738 device. tsop1738 is an integrated ir receiver which is able to receive ir signal at 38khz only, by doing so we cab reduce faulty ir signals coming from ambient light and other sources. These types circuit can be used in ir remote, tv remote controller. In olden days, these infrared remote can be used to control air conditioner systems. This is your diy ir transmitter. To design ir tv remote, you need to do a lot of work on ir codes given by particular manufacturer. That would be another tutorial in this blog. In this tutorial i am going to show ir trans circuit design first, later ir receiver circuit. This application will comes under 555 timer projects. you can design the same thing using microcontorller also. lm555 timer or ic 555 timer is an cheapest integrated circuit, where we can generate so many projects without using any microcontroller. This ir transmitter and receiver circuit using 555 timers is one of the popular 555 timer applications or 555 circuits.
Design of IR transmitter and receiver circuit
What is an IR ?
Infrared radiation exists in the electromagnetic spectrum at a wavelength that is longer than visible light. Objects that generate heat also generate infrared radiation such as animals and the human body.
|Figure 1: Electromagnetic spectrum|
In the Electromagnetic spectrum the infrared radiation covers the range from 300 GHz (1 mm) to 400 THz (750 nm). It can be divided into far-Infrared, mid-infrared, near infrared. In this section we mainly concentrate on mid-infrared because this range finds many applications in human life like TV remote control, object counter, etc.,
The mid-range IR ranges from 30 to 120 THz (10 to 2.5 μm). Hot objects (like black body radiators) can radiate strongly in this range. It is absorbed by molecular vibrations, where the different atoms in a molecule vibrate around their equilibrium positions.
So many IR diodes available in the market. These diodes also called as mid-range infrared diodes. One of the IR diode manufacturers is VISHAY INTERTECHNOLOGY. These diode are used in ir remote for tv controlling and other devices.
Design of IR transmitter using 555 timer
Here the design of the IR transmitter depends upon the receiver (TSOP sensor). This module requires the incoming data to be modulated at a particular frequency. It is also immune to ambient IR light, so one can easily use these sensors outdoors. TSOP sensors available for different carrier frequencies from 32 kHz to 42 kHz. Mostly available TSOP’s in the market are with a carrier frequency 38 kHz. Here in this project I used the TSOP with 38 kHz (TSOP 1738). In the number TSOP 1738 last two digits indicates the carrier frequency.
For such IR receiving sensor (TSOP), at the transmitter side we need to modulate the message signal with a carrier frequency. In this application I was generated a 38 kHz rectangular wave as a carrier and 1 kHz rectangular wave as a message (with a duty cycle less than 50% i.e., less Ton period than Toff period of the signal).
Generation of 38 kHz signal using 555 timer ic
astable multivibrator using 555 timer:
Note: When I was working on 555 timer circuit, I found that theoretical calculations are not exactly suitable for practical circuits. To generate 38 kHz rectangular wave, we need to operate the 555 timer in astable mode. The astable 555 timer doesn't require any trigger pulse. the figure 2 shows the 555 astable.
Frequency of oscillation of 555 timer circuit in astable mode is given as,
|figure 2: 38 kHz rectangular wave generator using 555 timer in astable mode for ir transmitter design in ir remote|
Fosc = -----------------------> (1)
Fosc = 38 kHz, assume C1 =0.01µF(always assume a fixed value capacitor because variable capacitor is difficult to find).
Substitute these values in equ (1)
Therefore, (Ra+2Rb) = = 3,763Ω.
Consider Ra as a fixed resistor = 1KΩ(say).
Obviously Rb = 1.382KΩ.
Practically, these resistor values in 555 astable may not generate exact 38 kHz signal. Hence for R2 value I use a POT (potentio meter or variable resistor). Use an oscilloscope to observe the signal at output pin3. Adjust the POT (variable resistor) until the signal at output is a 38 kHz. For proper values of RC and ic 555 pin diagram you can refer 555 timer pdf (datasheet)
Now similarly, generate 1 kHz signal with duty cycle less than 50%. Because the IR detector (TSOP) does not continuously detect the signal, it requires gap time between two detections see the image. The detection period is called burst time.
Burst length should be 10 cycles/burst or longer. After each burst which is between 10 cycles and 70cycles a gap time of at least 14 cycles is necessary.
Note: This gap time should have at least same length as the burst. For this purpose it is necessary to generate the message signal (1 kHz) with a duty cycle less than 50%.
Modulating of message signal (1 kHz) with carrier signal (38 kHz)
Quick tutorial for what is modulation and its importance:MODULATION IN COMMUNICATION SYSTEMS ANALOGY TO PAPER AND STONE EXAMPLE
by using modulation technique we can send the ir signal over longer distances like 9-10mts. Otherwise we won't able to send the signal atleast 1mt.
Here, the procedure to generate 1KHz signal is same as above .
Ra = 33Kohms as fixed resistor and adjust the preset for Rb value until you get exact 1KHz signal. Same capacitor values C1 = 0.01uf.
Modulated Output signal of ir transmitter for ir remote
To generated modulated signal, connect the output of 1kHz signal circuit (PIN3) to the RESET pin (PIN 4) of the carrier signal circuit which is not a monostable 555 timer.
NOTE: so many people facing problem with IR transmitter is distance that it cover.
Because of modulation we can transmit IR rays over a long distance.
we if the distance is increased we should provide more VCC supply(~ 12V) then the signal strength is good
|figure3: complete circuit diagram for ir transmitter circuit using 555 timer ic for ir remote|
Modulated Output Signal from 555 timer ir circuit
|Figure4: Modulated ir signal output from 555 based ir tranmitter circuit|