Joule Thief Circuit

Joule thief is a nickname for a minimalist self-oscillating voltage booster that is small, low-cost, and easy-to-build; typically used for driving light loads. It can use nearly all of the energy in a single-cell electric battery, even far below the voltage where other circuits consider the battery fully discharged (or "dead"). Hence the name suggests the notion that the circuit is stealing energy or "Joules" from the source

 

The circuit uses the self-oscillating properties of the blocking oscillator, to form an unregulated voltage boost converter. As with all power conversion technology, no energy is actually created by the circuit. Instead, the output voltage is increased at the expense of higher current draw on the input. As a result, the amount of power entering the circuit is the same as the amount leaving, minus the losses in the conversion process.

Clap Switch

Here’s a clap switch free from false triggering. To turn on/off any appliance, you just have to clap twice. The circuit changes its output state only when you clap twice within the set time period. Here, you’ve to clap within 3 seconds.

The clap sound sensed by condenser microphone is amplified by transistor T1. The amplified signal provides negative pulse to pin 2 of IC1 and IC2, triggering both the ICs. IC1, commonly used as a timer, is wired here as a monostable multivibrator. Trigging of IC1 causes pin 3 to go high and it remains high for a certain time period C3. This ‘on’ time (T) of IC1 can be calculated using the following relationship:

T=1.1R7.C3 seconds

where R7 is in ohms and C3 in microfarads. On first clap, output pin 3 of IC1 goes high and remains in this standby position for the preset time. Also, LED1 glows for this period The output of IC1 provides supply voltage to IC2 at its pins 8 and 4. Now IC2 is ready to receive the triggering signal. Resistor R10 and capacitor C7 connected to pin 4 of IC2 prevent false triggering when IC1 provides the supply voltage to IC2 at first clap.

On second clap, a negative pulse triggers IC2 and its output pin 3 goes high for a time period depending on R9 and C5. This provides a positive pulse at clock pin 14 of decade counter IC 4017 (IC3). Decade counter IC3 is wired here as a bistable.

Each pulse applied at clock pin 14 changes the output state at pin 2 (Q1) of IC3 because Q2 is connected to reset pin 15. The high output at pin 2 drives transistor T2 and also energises relay RL1. LED2 indicates activation of relay RL1 and on/off status of the appliance. A free-wheeling diode (D1) prevents damage of T2 when relay de-energises

A very simple IR remote control switch for an electrical appliance

This project describes a technique of adding the remote control feature to an electrical appliance. The goal is to construct a black box where you can plug-in your 240V AC appliance and control the ON and OFF operations with a ir remote.The good thing about this project is that it does not use any microcontroller and is only based on the CD4017 decade counter IC.

Microcontroller-Based Solar Charger

As the sources of conventional energy deplete day by day, resorting to alternative sources of energy like solar and wind energy has become need of the hour.

Solar-powered lighting systems are already available in rural as well as urban areas. These include solar lanterns, solar home lighting systems, solar streetlights, solar garden lights and solar power packs. All of them consist of four components: solar photovoltaic module, rechargeable battery, solar charge controller and load.

In the solar-powered lighting system, the solar charge controller plays an important role as the system’soverall success depends mainly on it. It is considered as an indispensable link between the solar panel, battery and load.

The microcontroller-based solar charge controller described here has the following features:

1. Automatic dusk-to-dawn operation of the load.
2. Built-in digital voltmeter (0V-20V range)
3. Parallel- or shunt-type regulation
4. Overcharge protection
5. System status display on LCD
6. Deep-discharge protection
7. Low battery lock
8. Charging current changes to ‘pulsed’ at full charge
9. Low current consumption
10. Highly efficient design based on microcontroller
11. Suitable for 10-40W solar panels for 10A load

courtesy:electronics4you

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