2 Simple Infrared (IR) Remote Control Circuits

The proposed infrared or IR remote control circuit can be used to operate an appliance ON/OFF through any standard TV remote control handset.

In this write up we discuss a couple of these simple infrared remote control circuits designed for controlling any given electrical appliance through an ordinary or TV remote control unit.

Introduction

Controlling household electrical gadgets or any electrical equipment remotely can be fun. Controlling gadgets like a TV set or a DVD player through a remote may look pretty common to us and we are very used to with the experience, however for controlling many other domestic equipment like a water pump, lights etc we are compelled to walk around for implementing the switching.

The article is inspired by our usual TV remote concept and has been applied for controlling other house hold electrical appliances remotely. The circuit facilitates and helps the user to do the operations without moving an inch from his resting place.

The whole circuit of the proposed IR remote control may be understood by studying the following points:

Referring to the figure, we see that the entire layout consists of just a couple of stages viz: the IR sensor stage and the flip flop stage.

Thanks to the highly versatile, miniature IR sensor TSOP1738 which forms the heart of the circuit and directly coverts the received IR waves from the transmitter unit into the relevant logic pulses for feeding the fllip flop stage.

The sensor basically consists of just three leads viz: the input, the output and the biasing voltage input lead. The involvement of only three leads makes the unit very easy to configure into a practical circuit.

The sensor is specified for operating at 5 volts regulated voltage which makes the inclusion of the 7805 IC stage important. The 5 voltage supply also becomes useful for the flip flop IC 4017 and is appropriately supplied to the relevant stage.

When a IR signal becomes incident over the sensor lens, the inbuilt feature of the unit activates, triggering a sudden drop in its output voltage.

The PNP transistor T1 responds to the negative trigger pulse from the sensor and quickly pulls the positive potential at its emitter to the collector across the resistor R2.

The potential developed across R2 provides a positive logic high to the IC 4017 input pin #14. The IC instantly flips its output and changes it’s polarity.

The transistor T2 accepts the command and switches the relay according to the relevant input provided to its base.

The relay thus switches the connected load across its contacts alternately in response to the subsequent triggers received from the IR transmitter unit.

For the sake of convenience the user may use the existing TV remote control set unit as the transmitter for operating the above explained control circuit.

The referred sensor is well compatible with all normal TV or DVD remote control handset and thus can be appropriately switched through it.

The entire circuit is powered from an ordinary transformer/bridge network and the entire circuit may be housed inside a small plastic box with the relevant wires coming out of the box for the desired connections.

Circuit Diagram

Video Demonstration

Parts List

The following parts will be required for making the above explained infra red remote control circuit:

• R1 = 100 ohms,
• R3 = 1K,
• R2 = 100K,
• R4, R5 = 10K,
• C1, C2, C4 = 10uF/25V
• C6 = 100uF/25V
• C3 = 0.1uF, CERAMIC,
• C5 = 1000uF/25V,
• T1 = BC557B
• T2, T3 = BC547B,
• ALL DIODES ARE = 1N4007,
• IR SENSOR = TSOP1738 image: Vishay
• IC1 = 4017,
• IC2 = 7805,
• TRANSFORMER = 0-12V/500mA,

TSOP1738 pinout Details

Prototype image courtesy: Raj Mukherji

2) Precision Infrared (IR) Remote Circuit

The second IR remote control circuit discussed below uses a unique frequency and detects only the specified IR frequency from the given remote transmitter unit, making the design entirely failproof, accurate and reliable.

Ordinary IR Remote Drawback

Ordinary IR remote control circuits have one big drawback, they easily get disturbed by stray external frequencies, and thus produce spurious toggling of the load.

In one of previous posts I have discussed a simple IR remote control circuit which operates quite well, however the circuit is not completely immune to external electrical disturbance generations such as from appliance switching etc. which results in false operations of the circuit causing lot of annoyance to the user.

The circuit design included here efficiently overcomes this problem without incorporating complex circuit stages or microcontrollers.

Why LM567 is Used

The solution comes easily due to the inclusion of the versatile IC LM567. The IC is a precise tone decoder device which can be configured to detect only a specified band of frequency, known as passband frequency. Frequencies not falling within this range will have no effect on the detection procedures.

Thus the passband frequency of the IC may be set precisely at the frequency generated by the transmitter IR circuit.

Shown below are the Tx (transmitter) and the Rx (receiver) circuits which are set precisely to complement one another.

T1 ad T2 along with R1, R2 and C1 in the first Tx circuit forms a simple oscillator stage which oscillates with a frequency determined by the values of R1 and C1.

The IR LED1 is forced to oscillate at this frequency by T1 which results in the transmission of the required IR waves from LED1

As discussed above, R5 of IC2 in the Rx circuit is adjusted such that its passband frequency precisely matches with that of LED1 transmission output.

Circuit Operation

When the Tx IR waves are allowed to fall over Q3 which is an IR photo transistor, a subsequent order of varying positive pulses is applied to pin#3 of  IC, which is basically configured as a comparator.

The above function generates an amplified output at pin#6 of IC1 which in turn gets induced across the input or the sensing pin out of IC2.

IC2 instantly latches on to the accepted passband frequency, and toggles its output at pin#8 to a low logic level, triggering the connected relay, and the preceding load across the relay contacts.

However the load would stay energized only as long as  Tx stays switched ON, and would switch OFF the the moment S1 released.

In order to make the output load latch and toggle alternately, a flip flop circuit will need to be employed at pin#8 of IC2.

Parts List

• R1 22K 1/4W Resistor
• R2 1 Meg 1/4W Resistor
• R3 1K 1/4W Resistor
• R4, R5 100K 1/4W Resistor
• R6 50K Pot
• C1, C2 0.01uF 16V Ceramic Disk Capacitor
• C3 100pF 16V Ceramic Disk Capacitor
• C4 0.047uF 16V Ceramic Disk Capacitor
• C5 0.1uF 16V Ceramic Disk Capacitor
• C6 3.3uF 16V Electrolytic Capacitor
• C7 1.5uF 16V Electrolytic Capacitor
• Q1 2N2222 NPN Silicon or Transistor 2N3904
• Q2 2N2907 PNP Silicon Transistor
• Q3 NPN Phototransistor
• D1 1N914 Silicon Diode
• IC1 LM308 Op Amp
• ICIC2 LM567 Tone Decoder
• LED1 Infa-Red LED
• RELAY 6 Volt Relay
• S1 SPST Push Button Switch
• B1 3 Volt Battery Two 1.5V batteries in series
• MISC Board, Sockets For ICs, Knob For R6,
• Battery Holder

Another Simple LM567 based IR Remote Control Circuit

The next accurate LM567 based IR transmitter/receiver circuit ensures that the remote control can be operated only through a preset fixed frequency, and will not operate through any other unknown frequency.

The transmitter circuit shown above produces IR light pulses through LED1, with a 320 Hz frequency (set by R2). This frequency is focused at the phototransistor Q1 of the receiver circuit. This causes the phototransistor's collector to oscillate at the same 320 Hz frequency. This frequency is boosted by the BC547 transistor and applied to the input pin#3 of the IC LM567.

The LM567 detects the 320 Hz signal as soon as it reaches the phototransistor, which instantly causes the output pin#8 of LM567 to turn low.

If the pulses of some other frequency is focused to the phototransistor, the LM567's output stays high and unresponsive, because it is calibrated to respond only for 320 Hz (as set by R6).

If you wish to operate the remote control with some other frequency, make sure to use identical values for R2 and R6, so that the transmitter frequency matches the receiver's detection frequency.

Remember that the LM567 operates between 100 Hz and 1 kHz and the detection frequency range must not be selected beyond these limits. A multi-channel remote control system may also be created by substituting R2 with additional number of resistors (for multiple frequencies) and LM567s set to the desired frequencies.

Switching an Output Load

If you want to switch an output load ON/OFF at pin#8 of the LM567, you can do it by integrating a 4017 IC flip flop circuit with pin#8 of LM567.

To implement this you just have to integrate the following 4017 flip flop relay circuit with pin#8 of the LM567 circuit explained above.

Simple Infrared Receiver using IC 741