Voice Recorder and Playback System (New)
There are several types of voice recorder and playback systems available in the market but most of them are expensive and their circuits are also very complex to assemble. Here is a simple circuit for recording and playback of voice messages. You can leave a voice message for your family or friends whenever you go out, which they can hear by pressing the ‘play’ button.
Key Chain Light (New)
A key chain with a built-in white LED comes in handy to help you at your front door or search your valuables in the dark. The intensity of white LED is 4000 to 5600 mcd (millicandela) at forward voltage of 3.6V and forward current of 20 mA.
Flashing Headlight For Mobikes (New)
The dipper for a vehicles headlight changes the light from high beam to low beam or vice versa given a particular set of road conditions. The shifting of light from high to low beam reduces the dazzle for those approaching head-on towards the vehicle. But the dip beam (or low beam) sometimes fails to attract attention of the riders coming from opposite direction.
Electrolytic Capacitor Tester (New)
Using this electrolytic capacitor tester you can detect leaky and dead (open) electrolytic capacitors. It operates based on the time constant (T) of the capacitor when it is charged up to 63 percent of the applied voltage via a known resistor.
LED Torch (New)
LEDs are becoming increasingly popular in many lighting applications. White LEDs are now common in torches. Here is a simple and economical LED torch that operates off two 1.5V cells.
Efficient LED Blinking for Embedded Systems
Smart hardware design can simplify the embedded software and make it more reliable. Designers use blinking LED signals to indicate different status and for inbuilt testability. Making an LED array blink requires an individual software loop for each LED or an individual timer and specific software to serve it. This can be an issue in a system that uses low-level MCUs which provide limited resources.
Fan On/Off Control by Light
This circuit lets you turn on/off a fan by just directing torchlight or other light toward its light-dependent resistor (LDR). The circuit is powered from a 5V power supply.
Keep away intruders with this compact electrified window charger. The charger produces non-lethal shocks that are strong enough to threaten intruders.
Versatile Proximity Detector with Auto Reset
Electrochemical processes taking place in our body generate complex sig-nals (hum) that are continuously being passed along the nerve fibres throughout the body. Any physical activity such as muscle movement increases hum.
Here is a low-cost circuit to convert 6V DC into 12V DC. It uses no transformer and is easy to construct with few components.
This circuit protects your television as well as other electrical appliances from over-voltage. It uses operational amplifier μA741 (IC1) as a comparator. The unregulated power supply is connected to resistor R3 and preset VR1 through resistor R2. Zener diode ZD1 provides reference voltage of 5.1V to the inverting input (pin 2) of IC1.
Presented here is a simple counter that counts the number of visitors entering or exiting an auditorium or any other place where you have installed this circuit at the gates. On receiving an interrupt from light-dependent resistor (LDR) sensors, the circuit increments the count and shows it on a 7-segment display.
Noise is a serious environmental problem that affects us in our daily life. There is scientific evidence supporting that noise exposure can cause hearing loss, hypertension, heart disease, annoyance, sleep disturbance and decreased performance in schools. Sound-level indicators like the one presented here can help address this problem. This sound-level indicator monitors the sound level and indicates through an LED when the level is above the preset value.
Earth Fault Indicator
In mains-powered equipment, exposed metal parts are connected to earth wire in order to prevent users from contact with high voltages if electrical insulation fails. Connections to ground through earth connection also limit the build-up of static electricity when handling electrostatic-sensitive devices. Earth in a mains electrical wiring system is a conductor that provides a low-impedance path to the earth to prevent hazardous voltages from appearing on equipment and hence the name.
RPM Meter for Automobiles
An efficient way to measure the RPM of a vehicle is through its ignition pulses. RPM of a vehicle is directly proportional to the rate of its ignition pulses. An ignition coil (also called spark coil) is an induction coil in an automobile ignition system that transforms the low voltage of the battery to the thousands of volts needed to create an electric spark in the spark plugs for igniting the fuel.
LED-Based Reading Lamp
This lamp circuit using ultra-bright white LEDs provides sufficient light for reading purposes while consuming approximately 3 watts of power. In the case of AC mains failure, the battery backup circuit instantly lights up the LEDs. When the power resumes, the battery supply is automatically disconnected and the lamp circuit again works off AC mains.
Hybrid Solar Charger
Efficiency of a solar charging system depends on the weather conditions. Usually the solar panel gets four to five hours of bright sunlight in a day. If the weather is cloudy or rainy, it affects the charging process and the battery does not attain full charge. This simple hybrid solar charger can solve the problem as it can charge the battery using both solar power as well as AC mains supply.
Transistor Polarity Checker
Presented here is a simple circuit that will help you figure out whether a transistor is npn or pnp type. If the transistor under test is npn, red LED will blink. If it is pnp, green LED will blink. This circuit is highly useful for small labs where components lie on the desk unidentified after a project is done and it is very tedious to read the part number printed on the component and identify it from its datasheet.