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12V Battery Absorb and Float Charger   

Most battery chargers stop charging the battery when it attains its maximum charging voltage set by the circuit. This circuit charges the battery at a particular voltage, that is, absorption voltage, and once the maximum charging voltage is attained, the charger changes the output voltage to float voltage for maintaining the battery at that voltage. Absorption and floating voltages are dependent on the type of battery.

Multichannel Visual Thermometer   

Temperature of some electronic components used in a device may rise unexpectedly and these might get damaged. This multichannel visual thermometer can indicate the problem through glowing LEDs. Since transistors are very cheap and widely available, this circuit uses these as low-cost temperature sensors and amplifiers.

Glass Break Alarm   

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.

Laser Based Security Lock   

Presented here is a security system that uses an inexpensive laser torch which is usually available with a key ring. The advantage of this security lock is that you can use any laser torch or pointer that is easily available in toy shops.

Bicycle USB Charger   

This circuit has been developed to add a USB charging port to a bicycle for charging a mobile phone.

Motion Detector Using NE555 Timer   

This circuit is based on a passive infrared (PIR) sensor, which automatically switches on a device when someone comes close to it. It can be used for detection of theft or an unauthorised person entering a restricted area or building.

Simple Adjustable Staircase Waveform Generator   

Staircase signals find many applications in the field of electronics, such as in television systems, telemetry, and analogue and digital communications. Here is a circuit illustrating the basic principles of staircase waveform generator.

Mini Offline UPS   

Here is a circuit of an offline UPS, which a hobbyist can make at a reasonable cost. The capacity of the UPS is 350VA, so it can be used for any equipment with a load below 350VA. The UPS can be upgraded to 1kVA by making just a few changes.

Letterbox with Letter-Counting Facility   

Here is a circuit that starts counting when you insert a letter in the letterbox at your home or office. It is designed to save your time from going to the letterbox to check if there are letters inside. The number of letters present in the box is indicated by a seven-segment display.

Low-Cost 6-Bit DAC   

For controlling the load of appliances such as cooling fans, low-wattage heaters, thermostats, low-wattage light sources, small electrical toys and test benches for loudspeakers, we need a power source whose voltage can be controlled in small steps and is capable of providing current of more than 1A. For that, we require low-resolution digital-to-analogue converters (DACs) with three to seven bits.Here is the circuit capable of setting output voltage between 1.25V and 15V in 64 steps.

GSM-based Dot-matrix Display   

Presented here is a GSM-based, eight-digit dot matrix display that can show an eight-digit message sent via any mobile phone, from any place around the world, to the mobile number of the SIM in the GSM module of the display. Size of the display is 740, which is made using 57 dot-matrix LED modules.

Parked-Vehicle Highway Flasher   

Often, at night, a speeding vehicle rams into another vehicle parked at the edge of a highway. Cars have parking flashers, but trucks, buses and loading rickshaws rarely have any form of a warning flasher. Here is a simple circuit of an effective flasher which is visible from a distance of up to 300 metres.

A Simple Musical Light   

The circuits for musical lights available in the market are highly expensive and based on microcontrollers. Also, their programming is very difficult. Here is a simple and cheap circuit for a musical light that you can build easily.

Mixer and Preamplifier for String Instruments   

This simple circuit can support up to four string instruments with electrical pickups and works as a mixer, preamplifier, driver and distortioner all at the same time with adjustable gain.

Telephone Sentry   

It is quite common to find extension phones in homes these days but this kind of convenience also comes with a distinct disadvantage: the possibility of another person listening in. This is where a telephone sentry comes in. This circuit, when attached to a telephone, is able to detect the presence of one or two additional telephones connected to the same line.

Multifunction Ozone Generator   

Ozone is a triatomic form of oxygen that is highly unstable and as such cannot be stored. It finds various applications in our daily life. For instance, it is used to detoxicate fruits and vegetables, disinfect wounds, remove bad odour, sterilise containers and clothes, and so on. Therefore a multifunction ozone generator circuit is presented here.

Shock-proof Remote Switch   

Using this circuit, you can control any AC/DC appliance remotely through inexpensive, low-voltage cabling and a standard push switch. The circuit can easily support cable length up to 25 metres.

Mini Rechargeable Power Supply   

Presented here is a robust, compact and hand-held power supply that delivers 9.2V and 5V up to 1A (approx.) and 3.3V up to 500mA. It also includes a female A-type USB connector so you can power and charge other equipment such as mobile phones. Four white LEDs are included to enable its use as a torch-light as well.

Simple 12V, 1A SMPS   

This is the circuit of a simple 12V, 1A SMPS. It is is built around a low-power offline switcher TNY266 (IC1), photo-transistor photo-coupler EL817 (IC2), a flyback transformer (X1) and some other easily-available components.

Electronic Door Lock   

Home burglary incidents are on the rise. Homes without proper security measures in place are particularly more vulnerable. But, it is easy to avoid home break-ins by using a simple solution like the electronic door lock presented here. With this circuit installed, the entry door of your house can be unlocked only by entering a pre-decided password, which helps to prevent unauthorised unlocking.



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