Matt circuit

Many modern electronic devices and micro-controller based circuits need a 5 V or 3.3 V power  supply. It is important  that  these voltages are constant and so a regulator of some kind is essential, including in battery powered devices. The simplest approach is to select a (perhaps rechargeable) battery whose voltage is rather higher than that required by the circuit and use an ordinary  linear voltage regulator. Unfortunately this solution is rather wasteful of precious energy and space: for a 5 V circuit at least six NiCd or NiMH cells would be required. Both these disadvantages can be tackled using a little modern electronics. A good way to minimise energy losses is to use a switching regulator, and if we use a regulator with a step-up topology then we can simultaneously reduce the number of cells needed to power the circuit. Fortunately it is not too difficult to design a step-up converter suitable for use in portable equipment as the semi-conductor manufacturers make a wide range...

The circuit of the cell phone-controlled audio/video mute switch . This cell-phone-controlled audio/ video mute switch is highly useful in automobiles. The circuit automatically disconnects power supply to the audio/video system whenever the mobile handset is lifted off the holder for making or receiving a call. You can use any readily available cell-phone holder with some mi-nor alterations or fabricate it yourself as shown in Fig. 1.  Fig. 1: Proposed cell-phone holder   The circuit is wired around IC LM555 (IC1), the CMOS version of timer NE555, as shown in Fig. 2. IC1 is used as a medium current line driver with either an inverting or non-inverting output. It can sink (or source) current of up to 50 mA only, so take care while handling it. The audio/video system is connected to the circuit via normally opened (N/O) contacts of the relay.   Fig. 2: The circuit of the cell phone-controlled audio/video mute switch   When the cell phone is in its holder, LDR1 does ...