@▷ Single Channel Universal Infared Switch by 555 Timer | Diagram for Schematic

Single Channel Universal Infared Switch by 555 Timer

Circuit Project Description

The circuit was designed to produce a universal infrared switch with a single channel and ON/OFF feature to operate in 36 kHz to 38 kHz in the form of a remote control.

TerminologyInfrared – a portion of the electromagnetic spectrum found between the microwave/radio waves and visible light region; contains a frequency range from 300 GHz to 400 THz and wavelength from 1 mm to 750 nmTSOP1738 – miniaturized receivers for standard IR remote control systems having the IR filter designed with epoxy package, the preamplifier and PIN diode assembled on lead frame, and the demodulated output signal directly decoded by a microprocessorCMOS inverter – a circuit containing complementary MOS transistor having either low or high input voltage with either high and low output voltage respectively555 Timer – an 8-pin electronic device used in several mixtures of applications involving multivibration and timingCircuit Explanation

The receiver side of the circuit is using the infrared that can be substituted by TSOP1738 to convert the received modulated infrared signal into electrical signal. It has features such as CMOS and TTL compatibility, improved shielding against electrical field interference, high sensitivity, high level of immunity to ambient light, integrated oscillator, 5V output, amplifies and receives the infrared signal without any external component, and encloses the preamplifier circuit and photodetector in the same housing.

For the relay to operate this universal switch, the button should be pressed for about 1.5 seconds as established by the resistor R3 and capacitor C2. Until doing a reset, the circuit will keep on at this condition. The reset happens by pressing any button for a short period in the remote handset. The buttons could be any type and be used in any remote control. Other electronic components, like a lamp, can be connected to the relay for as long as the rated current and voltage can be handled by the relay contacts.

IC1 functions as the infrared module that is responsible for buffering and receiving the IR modulated signal or pulses. The transistor-transistor logic (TTL) handles the standard output since it uses less power and is less sensitive from electrostatic discharge damage as compared to CMOS. The output is kept high by resistor R1 in the absence of signal. LED1 acts as a visible switching aid which is driven by one gate of a CMOS inverter, which consists of gates implementing logical negation of the input. The time constant circuit consists of D1, C2, R3 and R4 where the signal is buffered by another gate. The capacitor C2 discharges through R4 while it charges through R3. Through the low output impedance of the CMOS buffer, the quick discharge is avoided by D1. If IR1 will be replaced by TSOP1738, then resistor R4’s value need to be increased from 220K ohms to 470K ohms.

The RC time constant is calculated by the product of resistance and capacitance as this denotes the charging time by a capacitor. Only 63% of the voltage supply will be charged by a capacitor at one RC circuit while 99% of capacitor charging would require 5 RC circuits. The logic threshold of the CMOS inverter in this circuit is the reference point of charging for the capacitor. The input threshold is around 3.6V since the power supply is 5 Volts. This is equivalent to 3 RC circuits that will last for 1.5 seconds. CMOS inverter triggers the 555 timer upon reaching the threshold and will function as a memory circuit or flip flop where it will stay in two states of high output and low output.

As an illustration, although not the actual circuit, the figure shows a simulation of output pulse, filtering and received pulses. It only displays a spice simulation during the duration of 555 monostable with high pulses. The figure shows jiggered edges of the further buffered pulses which are produced by the IR modulated data. The jiggered edges are removed by the 555 timer functioning in monostable mode in IC3. The output of the pulse duration is determined by R5 and C4. To activate the bistable IC4, a clean output is required which will lead to creating a D type flip flop or latches. The bistable is built with a series IC of TTL 7474 which will cause the flip flop to act as a divide by two circuit and cause the pulse symmetric in ON and OFF times. However, other types of 7474 may also be employed like Schottky 74LS74. In this configuration, the inverted output is fed back to the data input an clear, the input is used to the clock pin, and preset lines are fixed to the ground. The relay will latch and operate for every pulse received while the next pulse will turn off the relay, and the cycle repeats. Because of the input delay imposed by R3, C2 is set for about 1.5 seconds so the fast turning ON and OFF of the relay is unlikely to occur.


Infrared has vast application in human lives. Shorter and near infrared waves in the form of handheld remote controls are mostly utilized in most video, radio and other electronic equipment using light signals within the IR range in a room. Used with IrDA ports, desktop computers, PDAs, printers and laptops are able to exchange information without using a cable connection by only requiring a line-of-sight transmission with half duplex connection and short range communication. Infrared amplifiers or IR blasters are typically used in home theater systems to deliver signals to all the components even behind as closed door. Night vision equipments are acquiring infrared in places with inadequate visible light. During the installation of a communications link, infrared lasers are used as free space optical communication for operating up to 4 Gbps in urban areas while in optical fiber communication, infrared lasers were used to provide lights.

In addition to the application of infrared, they are utilized by astronomers using lenses, mirrors, solid state digital detectors and optical components to monitor objects in the infrared region of electromagnetic spectrum. In chemotherapy induced oral ulceration treatment, photobiomodulation or near infrared light is used, as well as healing wounds. Infrared can be in the form of IR filters used for law enforcement, military, industrial and commercial purposes by allowing secrecy while obtaining a maximum infrared output. As a heating source, infrared are used in several industrial manufacturing procedures like plastic forming, print drying, plastic welding, curing of coatings and annealing. The radiation of infrared can be applied in identifying the temperature of objects remotely by using cameras, and is known as thermography. In meteorology, infrared or thermal images are produced by scanning radiometers used by weather satellites, for calculation of surface water and land temperatures, locating ocean surface features, and analysis of the types and heights of clouds. Infrared can also be used as a tracking or homing device by using the electromagnetic radiation emission of a target in passive missile guidance system. Analyzing of the constituent bonds of identified molecules uses the method of infrared vibrational spectroscopy. In infrared photography, camera phones and digital cameras are using infrared filters to capture near infrared spectrum. In the history of art, the underlying layers, outline or underdrawing drawn by the artist as a guide is revealed from the paintings using infrared refelctography. Since strong infrared radiation may be a health hazard to the vision and the eyes, eyeglasses which are IR proof are suitably used.

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