A remote control system for appliances makes our life smarter and easier. The wireless remote control circuit may be based on IR waves or RF waves, IR being cheaper. An IR emitter circuit is based on TSOP at the receiver section. Each TSOP operates at a particular frequency which depends on a number present on it. So each TSOP requires specific remote controller for its operation. There comes the importance of IR universal remote control which can be used to operate all normal hobby circuits.Here the basic principle of operation is Frequency Shift Keying (FSK). It enables to generate variable frequency so that it can detect different TSOPs.We are using two 555 timers here, both operating in astable mode which then drives the IR led.We shall discuss another transmitter circuit with microcontroller later in another article, which due to presence of crystal can generate the exact frequency.
Reason for this article:
In our previous articles on remote control lamp and remoter controlled DC motor we received some comments asking how to build a remote control, that’s why I decided to publish this one here.
My bathroom light used to be ON almost all the time as my family members were lazy enough to OFF the switch positioned a little bit away. So I decided to save the electricity by designing this IR TSOP loop to OFF the lamp. Firstly I used a 38 khz IR transmitter circuit for which I had to design an astable to generate that frequency. For this I used a potentiometer, but it was not working properly. It worked only when the potentiometer was being varied. So I implemented FSK to vary the frequency continuously.
Remote control transmitter schematic
- NE555 IC X2
- Transistor BC107; BC557
- Resistors (100KΩx2; 10KΩ; 470Ω; 100Ω; 1KΩx2; 330Ω 2.2KΩ)
- Capacitors (0.01uFx3; 2.2uF; 1uF)
- IR Led
- 9V battery
Working of infrared remote control
- One astable output is at lower frequency and other one at a higher frequency.
- Lower frequency multivibrator controls the frequency of the other.
- From the basic working principle of astable multivibrator, resistors R3, R4 and capacitor C4 determines the frequency, so the frequency can be changed by varying R3. This can be done simply by connecting a NPN transistor (BC 107) in parallel with R3 with a series resistance R5 to limit the current.
- Output of 555 is connected to the base of transistor through a current limiting resistor R7. When the output of first astable is high, the transistor BC107 becomes ON which in turn makes R5 parallel to R3. Then the total effective resistance goes below the resistance of lower resistor value, which reduces the time of astable 555. Thus increase frequency.
- Just the opposite process takes place when the first 555 output is low (OFF).
- Output of the second 555 is connected to an IR Led through a current limiting resistor R6. Led glows in accordance the output frequency which is then detected by the TSOP.
IR Sensor Circuit
- Here is a simple infrared detector circuit which gives a LED indication.
- TSOP gives active low output. So we are using a PNP transistor.
- When IR rays fall on the TSOP, then by the switching action of the transistor LED glows. You can remove the LED and resistor and connect any appliance you want with the help of relay.