OBJECTIVE Believe it or not, there are numerous occasions when you have switched. on your TV set to watch a specific program of your interest and you found out that there are still a few more minutes to go. The options before you are to either remain glued on to the TV get and wait for your program or switch off the TV set and then switch it on again after sometime. The first option is boring and with the second, you always run the risk of missing a part of the program if you get busy in something else and forget to switch it on in time. Here is a very simple and interesting gadget that could be very easily mounted on your electrical switchboard and which can be used to perform the auto switch on function for your TV set (or fortran matter any other mains operated system) at a time read more

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OBJECTIVE Here is a simple battery charger circuit, the one that can be used to charge 12 volt batteries of both the usual automobile type as well as the maintenance free sealed lead-acid type. The charger circuit being described here is quite   compact can be placed right on the top of the battery required to be charged. In the event of your car battery misbehaving or having become weak, what not require In addition to this gadget. Is only the |230VACmains.230VAC point is quite conveniently available even if you are stuck somewhere on the roadside or – elsewhere far away from a place where you can get your battery charged. This gadget could be one of the most important tools in your tool-kit and you could make use of this gadget to keep your battery healthy. Another significant read more

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OBJECTIVE The objective is to build a fully automatic emergency light that remains off in the normal circumstances and switching on automatically in the event of mains power failure. Such gadgets are very useful when used in places such as electricity meter box or the place where the various cut outs are located. The other useful places for these gadgets are cupboards and other dark corners where a little bit of light in case of power failure is of great utility. Another gadget that had similhttp://electricalandelectronics.org/2010/01/05ar application but was not automatic was discussed earlier in one of the projects. In that case, one needed to switch on the light manually at the location where the gadget is located. It causes a little bit of inconvenience when reaching that place in read more

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OBJECTIVE The circuit shown in Fig. 14.1 is that of a simple analog capacitance meter built around IC 555. It operates from a 9V battery and a provision for mains operation is also there. This test gadget can be used to measure capacitance values over a range from . 0.0001µF  to 100 µF. CIRCUIT DESCRIPTION The operational principle of this capacitance meter is quite straight forward. It is built around two 555′s, the first (IC-1) wired as an astable multivibrator and the second (lC-2) connected in the monoshot configuration and triggered by the 555 Wired in the astable mode. There is a 2-pole 6 throw (2P6T) rotary switch that can be used to i select the capacitance range. One half of this   rotary switch has been wired in the astable   multivibrator portion of the circuit read more

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OBJECTIVE An easy to build gadget that could give you a reminder after the preset time after you pressure start button is the project under discussion here. It is particularly   useful in situations where you         want to do something urgently but not immediately as you are busy doing something else and you would like to be reminded of that aftersome time. For instance, you have put something for cooking in the kitchen and you know that the next operation in cooking that dish is full 20 minutes away. So, you move to your bedroom and start reading some magazine. If you come across something engrossing to read, you would take your eyes off the magazine only after you get the burning smell   of the dish being cooked. There can be many more similar situations. All you have to read more

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OBJECTIVE Here is a simple and easy to build electronic gadget that can protect your TV or VCR or any other similar mains operable system from the hazards of operand under voltages. In our countly, Voltage fluctuation as large as ±40% is not unusual   with the result that most of the faults in these systems are due to power supply failure. While TVs and VCRs are more likely to be damaged due to excessive voltage, Refrigerators or Fridges are severely affected by extremely low voltages. Thus it is important to ensure that your system gets the correct AC mains voltage, of course, within a certain tolerance range which could be something like ±10%Though most of the modern TV sets and VCRs have a power supply section that can take care of fluctuations in the AC mains over a reasonably read more

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OBJECTIVE The objective here is to build a dual power supply that generates regulated +12 volts and -12 volts from 230VAC mains. Such a supply is a very common requirement in all those circuits that use opamps. Since opamps are very widely used in a variety of circuits of hobbyists’ interests, construction of this project could serve as a very useful tool in testing all those circuits that need a dual supply. Each of the outputs in the circuit shown in Fig.8.1 has a current delivering capability of 250mA. You would also discover this circuit to be an integral part of the more complex circuits that are mains operable.   CIRCUIT DESCRIPTION The unregulated AC/DC power supply part of the circuit consists of a transformer (T-1) that steps down 230VAC to 15 volts across a center read more

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Here we intended build a multi-purpose regulated power supply that will serve as a very useful alternative too our multiple needs of different battery eliminators to operate gadgets like Transistor sets, Audio Casette Recorders and so on and so forth. The circuit shown in Fig. 7.1 produces regulated output DC voltages of 3V, 6V, 9V and 12V that are selectable one at a time with the help of a rotary switch. Each one of the outputs is capable of delivering a load current of 500mA and can take care of wide fluctuations in the input AC. Intact, the output voltage remains at its nominal value for an input of 230AC  60 volts.It may be mentioned here that almost all battery eliminators available in the market for the purpose produce an unregulated output i.e., the output voltage varies with read more

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