CIRCUIT|| UHF REMOTE MAINS SWITCH TRANSMITTER

Designed to control the UHF Remote Mains Switch, this handheld transmitter can operate over a 200m range. It’s based on a PIC micro and a pre-assembled transmitter module, making it easy to build and get going.

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CIRCUIT|| CURRENT SENSOR

High-wattage appliances like electric irons, ovens and heaters result in unnecessary power loss if left ‘on’ for hours unnoticed. Here is a circuit that senses the flow of current through the appliances and gives audible beeps every fifteen minutes to remind you of power-’on’ status.

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CIRCUIT || A HIERARCHICAL PRIORITY ENCODER

Anormal priority encoder encodes only the highest-order data line. But in many situations, not only the highest but the second-highest priority information is also needed. The circuit presented here encodes both the highest-priority information as well as the second-highest priority information of an 8-line incoming data. The circuit uses the standard octal priority encoder 74148 that is an 8-line-to-3-line (4-2-1) binary encoder with active-‘low’ data inputs and outputs.

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Circuit || 9 LINE TELEPHONE SHARER

This circuit is able to handle nine independent telephones (using a single telephone line pair) located at nine different locations, say, up to a distance of 100m from each other, for receiving and making outgoing calls, while maintaining conversation secrecy.

Download Full Circuit: http://adf.ly/Vb89R

CIRCUIT || 15- STEP DIGITAL POWER SUPPLY

Here is a simple circuit to obtain variable DC voltage from 1.25V to 15.19V in reasonably small steps as shown in the table. The input voltage may lie anywhere between 20V down by closing switch S2.

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CIRCUIT || STEREO PREAMPLIFIER

This easy-to-build hi-fi preamp features high-performance audio op amps for ultralow noise and distortion. Its modular design incorporates five switched RCA phono inputs and support for a headphone amplifier.

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CIRCUIT || 40-METRE DIRECT CONVERSION RECEIVER

Using the circuit of direct-conversion receiver described here, one can listen to amateur radio QSO signals in CW as well as in SSB mode in the 40-metre band.

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ACCURATE ELECTRONIC STOP-WATCH

Here is a simple circuit which can be used as an accurate stop-watch to count up to 100 seconds with a resolution of 0.01 second or up to 1000 seconds with a resolution of 0.1 second. This stop-watch can be used for sports and similar other activities.

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CIRCUIT || Stereo Headphone Amplifier

Here’s a top-class headphone amplifier that can drive high or low-impedance phones to full power levels, with very low noise and distortion. For best performance, it can be teamed with the Stereo Preamplifier described last month. Alternatively, it can be used as a standalone unit, requiring only a power supply and a volume control potentiometer for use with any line-level signal source (CD/MP3 player). It even includes dual outputs, so you can listen with a friend!

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CIRCUIT || 7 MHz CW/AM QRP TRANSMITTERS

The circuit of a 7MHz C W / A M QRP transmitter described here can be used to transmit either CW or audio frequency modulated signal over a 7MHz carrier.

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CIRCUIT || 2-LINE INTERCOMCUM- TELEPHONE LINE CHANGEOVER CIRCUIT

2-LINE INTERCOMCUM- TELEPHONE LINE CHANGEOVER CIRCUIT

The circuit presented here can be used for connecting two telephones in parallel and also as a 2-line intercom. Usually a single telephone is connected to a telephone line. If another telephone is required at some distance, a parallel line is taken for connecting the other telephone. In this simple parallel line operation, the main problem is loss of privacy besides interference from the other phone. This problem is obviated in the circuit presented here. Under normal condition, two telephones (telephone 1 and 2) can be used as intercom while telephone 3 is connected to the lines from exchange.

Download Full Circuit: http://adf.ly/VtLiX