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

Glass Break Alarm Circuit Diagram

This circuit can be used for sounding an alarm to detect the breaking of a glass window by an intruder, even when the intruder ensures there is no sound of the shattered glass.

Fig. 1: Circuit of the glass break alarm
Fig. 1: Circuit of the glass break alarm

Circuit and working
Fig. 1 shows the circuit diagram of the glass break alarm. It is built around a piezo element connected across connector CON2, transistor BC549 (T1), timer NE555 (IC1), a piezo buzzer (PZ1) and a few other components.

A small piezo element used in the piezo buzzer is used as a sensor. It may be fixed at the centre of the window glass. IC1 is wired in monostable multivibrator mode, which is triggered by the piezo element. Output of IC1 is used to drive piezo buzzer PZ1. LED1 indicates the high-state output at pin 3 of IC1. Time delay can be adjusted by potentiometer VR1. Use an ordinary piezo buzzer at the output to generate a warning sound. This circuit works on 9V-12V DC.

When an intruder tries to break the glass, the piezo element generates an electric pulse, which is amplified and sent to the monostable multi-vibrator (IC1). The high output of IC1 drives LED1 and also produces a sound to indicate that someone is breaking the glass.

The 9V-12V DC power supply is connected across CON1, and the piezo element is connected across connector CON2.

Construction and testing
An actual-size, single-side PCB for the glass break alarm 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 the piezo buzzer sounds when someone tries to break the glass window. Fix the piezo element at the centre of the window glass for best results.

Fig. 2: Actual-size PCB of the glass break alarm

Fig. 3: Component layout of the PCB

Use of 8-pin IC base is recommended for IC NE555.

Sourced by: EFY. Author : Pradeep G.

Automatic Dipper for Vehicles Project

While driving a car in night a problem like many drivers do not dip the head lamps of their vehicles in night while approaching. The several switching operation is used to dip the head light which may distract the concentration. To overcome this type of problem the innovative group Dreamlover Technology designs a unique electronics gadget called “Automatic Dipper” using very popular IC NE555 and LDR.

Circuit Description

The entire circuit of automatic dipper consist LDR followed by timer IC NE555 (IC1) and few other components, where LDR is used as sensor. LDR sense the light and change its internal resistance according light fall on it, which is further mounted in PVC pipe of 4 cm length positioned on the grill of car or in front such that the light fall on the LDR only when vehicles is approaching and is distance of 3M to 9M. When light fall on it the resistance decrease and makes output of IC1 low which energized the relay. The relay operates and voltage across the head lamps is reduced. When the distance between two approaching vehicles is more than 9 meter or less than 3 meter the circuit is not operated.

Automatic Dipper for Vehicles Circuit Diagram 

Automatic Dipper for Vehicles

The operating and non operating distance of the circuit can be varied by proper positioning of the PVC pipe and by adjusting the variable resistor VR1.

Resistors (all ¼-watt, ± 5% Carbon)

R1 = 10 Ω/10W

VR1 = 10 KΩ

IC1 = NE555 (timer IC)

D1 = 1N4001

RL1 = 12V/100 Ω

LDR1= Light dependent resistor

Sourced by:  electronicsproject

Electronic siren circuit Diagram

This is a compact electronic siren circuit based on three transistors.This circuit is suitable for in corporating with other alarm or siren projects such as burglar alarms, automatic factory sirens etc or a simple push to on alarm.

The  electronic siren circuit given here  is  based on a complementary transistor pair consisting of Q2 & Q3 (BC557 & BC 37)  wired as an astable multivibrator oscillator,which directly drives the speaker.The transistor Q1 is used to provide a full charge on capacitor C2 when power is turned ON. When push button switch S1 is pressed , the capacitor C2 slowly discharges through resistor R8.This makes the circuit to  oscillate at a low frequency that increases to a high frequency and kept indefinitely as the capacitor is fully discharged. When the switch P1 is released, the output  frequency decreases slowly as C2 is charged to the  positive voltage through resistance R6 and the Base-Emitter junction of tramsistor Q2. When C2 is fully charged to the positive battery voltage the  circuit stops oscillating.

Electronic siren circuit Diagram with Parts list.

Electronic siren circuit Diagram


  • A 12 V battery or a a well regulated 12V DC power supply can be used to power the circuit.
  • Assemble the circuit on a good quality PCB or common board.
  • The switch S1 can be used to activate the alarm.
  • The switch S2 can be used as a power switch.
  • You can experiment on the tone of alarm by using different values for C2 and R8.

Sourced By: circuitstoday


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