This is not very critical and any other device (such as tape player with message recorded on an endess tape) which does not overload the circuit or the telephone line, may be used. The incoming line is protected by metal-oxide varistor (MOV) RDN 130/14 followed by polarity guard circuit comprising diodes D1 through D4 in bridge configuration. Tran
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sistor T1 (MPSA92), having a high breakdown voltage (Vce max. ) is used as electronic switch/telephone line interface. It is controlled by transistor T2. Ring detector section comprises capacitor C1, resistor R10 and opto-coupler NEC 2505. (In case of its non-availability, one may substitute it with MC2TE or a similar opto-coupler with additional diode 1N4148 placed with its cathode connected to pin 1 and anode to pin 2 of the opto-coupler. ) Timer NE555 (IC1), configured as monostable flip-flop, is powered by external 230V AC via transformer X1, rectifier diodes D5, D6 and filter capacitor C5. When switch S1 is on, the incoming telephone line as well as transformer X1 get connected to the circuit and D8 LED lights up. Normally the monoshot IC1 is off (output at pin 3 is low) and so also are the transistors T1, T2 and relay RL1. When ring is received, the opto-coupler operates and takes trigger pin 2 of timer from high-to-low potential, thereby triggering it. This causes the output at pin 3 of IC1 to go high, which causes relay RL1 to energise and create a bypass for the ringing voltage to the opto-coupler as transistor T2 also gets forward biased. Conduction of transistor T2 causes forward biasing of switching transistor T1. This, in turn, causes the positive votage from rectifier diodes D3, D4 cathode junction to be extended to voice IC chip after being limited to steady 6. 2 volts by resistor R3, zener D10 and capacitor...
This project fits more for custom made battery casing that can have more space to hide things inside. This switch with few alterations can be used for any other project as well but is designed based on e-bike needs! This project use a clever functionality of....
The circuit described here uses ultrasonic oscillations and operates based on the propagation velocity of these oscillations in the air. Thus, we can easily determine the distance of two points if the time within which the wave travels this distance is....
Sometimes the precious metals are hidden too deep and are not detected except with complicated devices. In many cases, however, small pieces of precious metal buried near the surface can be detected by relatively simple means. Everyone is very attractive to....
Many times for various reasons we forget or can not water the plants that we have in our homes. And many humidity sensors units just notify us with a beeping sound or with a flashing light, that the pot needs watering. But what if we are away from home? This....
The principle behind a metal detector is really very simple. Proof of this is the circuit that follows, in which it proves that the construction of a metal detector can be done in the minute, with few components that we find very easily everywhere. With the....
The sub-harmonic bass generator is a sound producing unit for guitars. The sound it produces looks very much like that of the bass guitar. The octave generator is sometimes quite unusual since it does not produce any of the usual ways of coloring the sound,....
In the past the sounding (sea bottom measurement) was done with the "bullet", that is, with a heavy lead object that the seamen plucked into the sea hung from a calibrated rope. As soon as the "bullet" reached the bottom, the depth appeared directly from the....
This Amplifier was designed to have the following specifications: Distortion less than 0.1% at full power of 100W even at 20KHz. Power has to be attributed to an extended bandwidth. The output transistors must be protected against short circuits. The power....
A series of LEDs serve to alert the gardener when plants need water. Using two conventional digital integrated LEDs and a series of LEDs, we make a very useful device for gardening. The device detects the amount of water in the pot and alerts the grower.....
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