Wireless Security System Using PIR Sensors Project

This project demonstrates a wireless security system in which four pyroelectric infrared (PIR) motion sensors are placed in four sides—front, back, left and right—of the area to be covered. It detects motion from any side and turns on the audio-visual alarm. It also displays the side where the motion (intruder) is detected. All sensors send signal to the central controller circuit wirelessly. The author’s prototype arrangement is shown in Fig. 1.

Wireless Security System Using PIR Sensors Project
 Fig. 1: Author’s prototype arrangement for Wireless security system

System block diagram

System block diagram of the wireless security system is shown in Fig. 2. The project uses PIR motion sensors to detect motion and ASK-based radio frequency (RF) transmitter and receiver modules to send signals wirelessly. It uses AT89S52 microcontroller (MCU) and LCD to display the side where the motion is detected.

 Fig. 2: Block diagram of wireless security system using PIR sensors

The block diagram has two parts: four transmitter units with PIR sensors, encoders and RF transmitters; and receiver unit with RF receiver, decoder, MCU and some audio-visual circuits.

Transmitter unit

There are four transmitter blocks, one each for front, back, left and right sides. Each block consists of a PIR sensor, RF encoder chip and RF transmitter (Tx) module.

PIR sensor

The PIR sensor detects motion by measuring any change in IR levels emitted by objects. Pyroelectric devices have elements made of a crystalline material, which generate an electric current when exposed to IR radiation. Changes in the amount of IR falling on such devices changes the voltages that are generated. Sensor output goes high when it detects motion. Sensor output is given to RF encoder chip.

RF Encoder

HT12E encoder chip encodes PIR sensor output into serial bit streams and gives it to RF Tx module.

RF transmitter

ASK transmitter modulates incoming digital signals from the RF encoder using a 434MHz carrier and transmits it through its antenna.

Receiver unit

This is the central controlling section that receives signals from any of the four PIR sensors at the transmitter side. It gives audio and visual alarms, and displays the side where the motion is detected on LCD1.

RF receiver

This module operates on 434MHz frequency and demodulates the received digital signals before sending bit streams to RF decoder chip.

RF decoder

HT12D RF decoder chip decodes bit streams and generates parallel 4-bit digital output, which is given to the MCU.


AT89S52 MCU performs the following tasks:

1. Detects side where motion is detected from RF decoder digital output

2. Displays various messages including side of detected motion on LCD1

3. Turns on speaker and blinks LED for audio-visual alarm when motion is detected
LCD panel

The 16×2 LCD panel displays messages given by the MCU.


There are two multivibrators. One for blinking the LED at low frequency (1Hz – 2Hz), and the other for generating the audio frequency signal (1kHz) through the speaker for siren.

Circuit and working

There are five circuits. Of these, four transmitter circuits are similar to each other, with minor changes, as shown in Fig. 3. Fifth circuit, as shown in Fig. 4, is the receiver circuit.

Wireless Security System Using PIR Sensors circuit
Fig. 3: The four transmitter circuits

Wireless Security System Using PIR Sensors circuit 1
 Fig. 4: Circuit diagram of MCU-based central receiver circuit

Transmitter circuit

The first transmitter circuit is built around IC1. Output of PIR sensor PS1 is given to data input AD8 (pin 10) of HT12E (IC1) after inverting it through transistor T1. Diodes D1 and D2 connect transmission enable (TE) pin with pin AD8, so that both pins get input from the sensor at the same time.

LED1 is connected to collector output of T1, so that it blinks when PS1 sensor output goes high. Address pins A0 through A7 of IC1 are connected to ground to set address 00 (0000 0000b). Serial data output DOUT (pin 17) is given as data input to 434MHz RF Tx module (TX1). The whole circuit is given power through 6V battery (BATT.1) connected across CON1.

The other three circuits are shown in Fig. 3 are similar to the one described above. The only difference is that the diode is connected to different data pins.

When PIR sensor PS1 detects motion, its output goes high. T1 conducts and LED1 blinks.

Pins AD8 and TE of IC1 are pulled low together through diodes D1 and D2. When TE pin is pulled low, IC1 transmits address A0 through A7, and AD8 through AD11 serially through RF Tx module. Because pin AD8 is pulled low, data bits are transmitted as 1110 (AD11 through AD8). Similarly, in other such circuits, when motion is detected, the respective data pin is pulled low, so different data is transmitted, as listed in Table I.

Thus, when a sensor detects motion from its side, different bit pattern of D0 through D3 is transmitted. At receiver side, this pattern is used to identify the side where motion is detected.
Receiver unit

As shown in Fig. 4, the receiver is built using 434MHz RF Rx module (RX1), RF decoder chip HT12D (IC5), AT89S52 MCU (IC6) and NE555 multivibrators (IC7 and IC8).

Sourced By : EFY Author:  Ashutosh M. Bhatt

Short-Wave Superregenerative Receiver Circuit Diagram

Short-Wave Super regenerative Receiver Circuit diagram. Super regenerative receivers are characterized by their high sensitivity. The purpose of this experiment is to deter-mine whether they are also suitable for short-wave radio. Super regenerative receivers are relatively easy to build. You start by building a RF oscillator for the desired frequency. The only difference between a super regenerative receiver and an oscillator is in the base circuit. Instead of using a voltage divider, here we use a single, relatively high-resistance base resistor (100 kΩ to 1MΩ).

Super regenerative oscillation occurs when the amplitude of the oscillation is sufficient to cause a strong negative charge to be applied repeatedly to the base. If the regeneration frequency is audible, adjust the values of the resistors and capacitors until it lies somewhere above 20 kHz. The optimum setting is when you hear a strong hissing sound. The subsequent audio amplifier should have a low upper cutoff frequency to strongly attenuate the regeneration signal at its output while allowing signals in the audio band to pass through. This experimental circuit uses two transistors. A Walkman headphone with two 32-Ω earphones forms a suitable output device. 

Short-Wave Super regenerative Receiver Circuit diagram :

Short-Wave Super regenerative Receiver Circuit diagram

Short-Wave Super regenerative Receiver Circuit Diagram

The component values shown in the schematic diagram have proven to be suitable for the 10–20 MHz region. The coil consists of 27 turns wound on an AA battery serving as a winding form. The circuit produces a strong hissing sound, which diminishes when a station is received. The radio is so sensitive that it does not require any antenna to be connected. The tuned circuit by itself is enough to receive a large number of European stations. The circuit is usable with a supply voltage of 3 V or more, although the audio volume is greater at 9 V. 

One of the major advantages of a super regenerative receiver is that weak and strong stations generate the same audio level, with the only difference being in the signal to noise ratio. That makes a volume control entirely unnecessary. However, there is also a specific drawback in the short-wave bands: interference occurs fairly often if there is an adjacent station separated from the desired station by some-thing close to the regeneration frequency. The sound quality is often worse than with a simple regenerative receiver. However, this is offset by the absence of the need for manual feedback adjustment, which can be difficult. 

Author :Burkhard Kainka  - Copyright : Elektor

12V to 230V DC To AC Inverter Circuit Diagram

This is a simple DC to AC inverter circuit project to convert a 12V DC battery become 230V AC. By doing simple modification you can also convert 6V DC to 230V AC or 110V AC. It can be used to power up the electronic devices which require low electrical consumption. For example for home needs to enable light loads (electric bulb, CFL, etc) at the time of electricity failure, smartphone charger, etc.

12V to 230V DC To AC Inverter Circuit Diagram
12V to 230V DC To AC Inverter Circuit Diagram

    Inverter, is an electronic device or circuitry that changes direct current (DC) to alternating current (AC). The input voltage, output voltage and frequency, and overall power handling depend on the design of the specific device or circuitry. The inverter does not produce any power; the power is provided by the DC source.

DC to AC Inverter Component List
  •     IC CD4047
  •     Resistors (1K, 18K, 100Ω- 0.5W x 2)
  •     Capacitor (0.22µF)
  •     12V rechargeable battery
  •     IRFZ44 MOSFET x 2
  •     Step Down Transformer (230V primary 12V-0-12V, 5A secondary) (110V to 12V-0-12V, 5A can also be used) NB:- Transformer connection inverted

How the DC to AC Inverter Works
  •     The inverter circuit is built around IC CD4047 which is wired as astable multivibrator.
  •     The operating frequency of astable multivibrator is set to 50Hz.
  •     The power MOSFETs IRFZ44 are directly driven by the Q and Q’ output of CD4047.
  •     The power MOSFETs are connected in Push Pull configuration (Power amplifier). The MOSFETs will switch according to the pulse from CD4047 astable multivibrator.
  •     Thus an AC voltage is transferred to the primary of transformer; it is stepped up to 230V.

DC to AC Inverter Notes
  •     The transformer used here is an ordinary step down transformer which is connected in inverted manner. That is, the primary of a 230V to 12V-0-12V step down transformer can be treated as secondary for this inverter project.
  •     If you would like to get 110V AC, choose 110V to 12V-0-12V step down transformer in reversed way. (That is primary as secondary and secondary as primary)
  •     The inverter output is filtered by capacitor C2.
  •     Use suitable heat sinks for MOSFETs.

Sourced By: inverter-circuit

Wireless Baby Monitor Circuit Project

A baby monitor can help you find peace of mind. You can now monitor your sleeping baby with this wireless baby monitor. It is a radio system used to remotely listen to sounds made by an infant. Simply place the circuit near your sleeping baby and listen through an FM receiver from any other room in the house. It can also alert you if the baby wakes up in the middle of the night.

 Wireless Baby Monitor Circuit Diagram
 Wireless Baby Monitor Circuit Diagram

The circuit is built around a low-power audio amplifier using LM386 (IC1), hex inverting Schmitt trigger 74HC14 (IC2), voltage regulator 7805 (IC3), 10MHz crystal (XTAL1), varactor diode 1SV149 (D1) and a few other components. A parallel resonant oscillator circuit is formed around inverter gate N1 along with crystal (XTAL1), resistor R3, capacitors C3 and C4 and varactor diode D1. It generates square waves at the fundamental frequency of 10MHz of crystal.

Fig. 2: PCB of the baby monitor circuit

The signal is buffered by gate N2 and further boosted by parallel inverter gates N3, N4, N5 and N6. Unlike sine waves, square waves have many harmonics above their fundamental frequency. The monitor transmits on tenth (100MHz) harmonics of the square wave. Use a quarter-wave 75cm piece of wire for the antenna.

Fig. 3: Component layout of the PCB

The audio section of the transmitter is built around IC1. The gain is set to 200 by capacitor C2. Audio from electret microphone MIC1 is picked up and amplified by LM386. It is then coupled with varactor diode D1 via resistor R2. The crystal’s frequency along with D1 forms an FM modulation signal. Since the circuit transmits on tenth harmonic of crystal frequency, audio deviation is also multiplied by a factor of 10. This results in clear audio that can be received on an FM receiver.

Construction and testing
An actual-size, single-side PCB for the baby monitor circuit is shown in Fig. 2 and its component layout in Fig. 3. Keep all leads as short as possible. After assembling the circuit on a PCB, enclose it in a suitable plastic box. Drill a small hole for the microphone. Use 12V to power the circuit. The current consumption of the circuit is very low. Before using the circuit, ensure that power supply is correct.

Sourced By : EFY

An Electronic Watering Can Circuit Diagram

An Electronic Watering Can Circuit Diagram. Summertime is holiday time but who will be looking after your delicate houseplants while you are away? Caring for plants is very often a hit or miss affair, sometimes you under-water and other times you over-water. This design seeks to remove the doubt from plant care and keep them optimally watered. 

The principle of the circuit is simple: first the soil dampness is measured by passing a signal through two electrodes placed in the soil. The moisture content is inversely proportional to the measured resistance. When this measurement indicates it is too dry, the plants are given a predefined dose of water. This last part is important for the correct function of the automatic watering can because it takes a little while for the soil to absorb the water dose and for its resistance to fall. If the water were allowed to flow until the soil resistance drops then the plant would soon be flooded.

An Electronic Watering Can Circuit Diagram

An Electronic Watering Can Circuit Diagram
An Electronic Watering Can Circuit Diagram

The circuit shows two 555 timer chips IC1 and IC2. IC1 is an astable multivibrator producing an ac coupled square wave at around 500 Hz for the measurement electrodes F and F1. An ac signal reduces electrode corrosion and also has less reaction with the growth-promoting chemistry of the plant. Current flowing between the electrodes produces a signal on resistor R13. The signal level is boosted and rectified by the voltage doubler produced by D2 and D3. When the voltage level on R13 is greater than round 1.5 V to 2.0 V transistor T2 will conduct and switch T3. Current flow through the soil is in the order of 10 µA. 

T2 and T3 remain conducting providing the soil is moist enough. The voltage level on pin 4 of IC2 will be zero and IC2 will be disabled. As the soil dries out the signal across R13 gets smaller until eventually T2 stops conducting and T3 is switched off. The voltage on pin 4 of IC2 rises to a ‘1’ and the chip is enabled. IC2 oscillates with an ‘on’ time of around 5 s and an ‘off’ time (adjustable via P2) of 10 to 20 s. This signal switches the water pump via T1. P1 allows adjustment of the minimum soil moisture content necessary before watering is triggered. 

The electrodes can be made from lengths of 1.5 mm2 solid copper wire with the insulation stripped off the last 1 cm. The electrodes should be pushed into the earth so that the tips are at roughly the same depth as the plant root ball. The distant between the electrodes is not critical; a few centimetres should be sufficient. The electrode tips can be tinned with solder to reduce any biological reaction with the copper surface. Stainless steel wire is a better alternative to copper, heat shrink sleeving can used to insulate the wire with the last 1 cm of the electrode left bare. Two additional electrodes (F1) are con nected in parallel to the soil probe electrodes (F). The F1 electrodes are for safety to ensure that the pump is turned off if for some reason water collects in the plant pot saucer. A second safety measure is a float switch fitted to the water reservoir tank. 

When the water level falls too low a floating magnet activates a reed switch and turns off the pump so that it is not damaged by running with a dry tank. Water to the plants can be routed through closed end plastic tubing (with an internal diameter of around 4 to 5 mm) to the plant pots. The number of 1 mm to 1.5 mm outlet holes in the pipe will control the dose of water supplied to each plant. The soil probes can only be inserted into one flowerpot so choose a plant with around average water consumption amongst your collection. Increasing or decreasing the number of holes in the water supply pipe will adjust water supply to the other plants depending on their needs. A 12 V water pump is a good choice for this application but if you use a mains driven pump it is essential to observe all the necessary safety precautions. 

Last but not least the electronic watering can is too good to be used just for holiday periods, it will ensure that your plants never suffer from the blight of over or under-watering again; provided of course you remember to keep the water reservoir topped up…

Author : Robert Edlinger

USB Standby Killer Circuits Diagram

When turning a computer on and off, various peripherals (such as printers, screen, scanner, etc.) often have to be turned on and off as well. By using the 5-V supply voltage from the USB interface on the PC, all these peripherals can easily be switched on and off at the same time as the PC. This principle can also be used with other appliances that have a USB interface (such as modern TVs and radios). 

USB Standby Killer Circuit Diagram :

USB Standby Killer Circuits Diagram

This so-called ‘USB-standby-killer’ can be realised with just 5 components.
The USB output voltage provides for the activation of the triac-opto driver (MOC3043) which has zero-crossing detection. This, in turn, drives the TRIAC, type BT126. 

The circuit shown is used by the author for switching loads with a total power of about 150 W and is protected with a 1-A fuse. The circuit can easily handle much larger loads however. In that case and/or when using a very inductive load a so-called snub-ber network is required across the triac. The value of the fuse will also need to be changed as appropriate. 

The circuit can easily be built into a mains multi-way power board. Make sure you have good isolation between the USB and mains sections (refer to the Electrical Safety page published regularly in this magazine). 

Simple 250W Inverter Circuit Diagram

This is the Simple 250W Inverter Circuit Diagram.In this time a 555 timer (IC1) generates a 120-Hz signal that is fed to a CD4013BE flip-flop (ICl-a), which divides the input frequency by two to generate a 60-Hz clocking frequency for the FET array (Ql through Q6).Transformer Tl is a 12-/24-V center-tapped 60-Hz transformer of suitable size. 

Simple 250W Inverter Circuit Diagram

Simple 250W Inverter Circuit Diagram

 Sourced by: www.circuitsstream.com

Light and Sound Indicator for Mains Power Supply Project

While repairing or installing electrical machines in a building, the AC mains power supply is switched off from the mains electrical switchboard installed outside the building. There is a chance that someone who is not aware of the same may switch on the mains from outside. This poses a great danger for the technician working inside. Hence, an indicator like the one described here, which can be plugged into a nearby mains wall socket, might prove very useful for the technician.

This circuit can also be useful for people who are living in a place where there is frequent mains power cut.

Circuit and working
The circuit diagram of the light and sound indicator for the mains power supply is shown Fig. 1. The circuit is built around capacitors C1 and C2, resistors R1 and R2, diode D1, zener diode ZD1, LED1 and a piezo buzzer (PZ1). Resistor R1 and capacitor C1 are used for reducing the voltage and limiting the current. Diode D1 is a rectifier.

C2 is used as a filtering capacitor. Zener diode ZD1 limits the output voltage to around 12V. The value of zener diode should be equal to or lower than the maximum voltage of the buzzer and higher than the minimum voltage. Preferably, the buzzer should have a built-in oscillator working in the range of 6V-12V and requiring a current below 10mA. The frequency of the alarm sound is usually in several kilohertz (kHz).

LED1 is on when the mains power supply is present, and at the same time the buzzer produces sound. Resistor R1, capacitor C1 and diode D1 are selected depending on the current requirement of the buzzer.

Circuit diagram of the mains power indicator
Fig. 1: Circuit diagram of the mains power indicator

Fig. 2: Actual-size, single-side PCB of the indicator

Fig. 3: Component layout of the indicator

Construction and testing
An actual-size, single-side PCB of the simple light and sound indicator is shown in Fig. 2 and its component layout in Fig. 3. Enclose the PCB in a suitable small box in such a way that you can use it during repair work or installation. Ensure proper wiring to avoid any mistake.

Sourced by: EFY

Petre Tzv Petrov was a researcher and assistant professor in Technical University of Sofia, Bulgaria, and expert-lecturer in OFPPT, Casablanca, Kingdom of Morocco. He is currently working as an electronics engineer in the private sector in Bulgaria


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