Audio-Visual Extra Ringer for Phone

Many a times one needs an extra telephone ringer in an adjoining room to know if there is an incoming call. For example, if the telephone is installed in the drawing room you may need an extra ringer in the bedroom. All that needs to be done is to connect the given circuit in parallel with the existing telephone lines using twin
flexible wires. This circuit does not require any external power source for its operation. The section comprising resistor R1 and diodes D5 and LED1 provides a visual indication of the ring. Remaining part of the circuit is the audio ringer based on IC1 (BA8204 or ML8204). This integrated circuit, specially designed for telecom application as bell sound generator, requires very few external parts.
It is readily available in 8-pin mini DIP pack. Resistor R3 is used for bell sensitivity adjustment. The bell frequency is controlled by resistor R5 and capacitor C4, and the repetition rate is controlled by resistor R4 and capacitor C3.

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LOW BUDGET INTERCOM

THE central component in this Intercom project is an integrated circuit designed for audio amplification, type LM386. It is shown as IC1 in Fig.4.3. The circuit shows that it needs few additional components to do its job of amplifying audio signals. The internal voltage gain is set at 200 by capacitor C2, connected between
pins 1 and 8. Two low-power loudspeakers, LS1 and LS2, act as microphone or speaker depending on the position of the double-pole, double-throw reversing switch, S2.

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Everyday Practical Electronics, January 2009

PHONE/FAX MISSED CALL ALERT

Constructional Project This device detects an incoming call on your phone or fax and lights an LED and latches on a relay, which you can use to switch on a lamp or horn in another room or your garage.

So what’s wrong with listening for the phone ringer or looking at the fax machine’s ‘out’ tray? If you work

at home you need to be able to respond to phone calls or faxes as soon as they come in, but you cannot be hovering over the phone all day; there are times when you have to leave your office or home and if you do not physically lift the phone handset and listen (if you have BT Answer 1571) or check the fax as soon as you arrive back, calls or faxes could be without a response for some time. 

Or maybe you have an office but spend some time in the workshop. Same problem – or even more so if you are waiting on an important call or fax. So this is the remedy. Build this device and it will let you know that a phone call has been made or a fax has been received, without you needing to actually check the phone or fax.

What’s more, you can use it with a remote light or siren to alert you over the noise of machinery!

The Phone/Fax Missed Call Alert hooks up easily to the fax machine’s phone line. It connects in very easily, using a standard low-cost modular cable. The kit of parts should set you back no more than about £15 and you should be able to build it up in a couple of hours at most.

How it works

When someone dials your phone or fax number, the exchange sends out short (200ms) bursts of a 75V 17Hz AC signal – the ‘ring signal’. It’s this signal that causes your phone to ring or triggers the fax machine into answering and receiving the message. Our Missed Call Alert is designed to monitor the phone line and respond to the same ring signal, using it to trigger a flipflop and hence latch a relay.

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By JIM ROWE
Everyday Practical Electronics, January 2008

ANTI-THEFT SECURITY FOR CAR AUDIOS

This small circuit, based on popular CMOS NAND chip CD4093, can be effectively used for protecting
your expensive car audio system against theft.

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Add on stereo channel selector

The add-on circuit presented here is useful for stereo systems. This circuit has provision for connecting stereo outputs from four different sources/channels as inputs and only one of them is selected/ connected to the output at any one time.

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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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