This system uses a transmitter at around 100 kHz (see Fig. 86-3(a)) to control a remote rece
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iver. A line splitter can be used to connect the transmitter to the telephone line in use. The transmitter is a CMOS oscillator and has output buffer stages to drive the telephone line. When the receiver (Fig. 86-3(b)) detects the off-hook condition (the line voltage drops from about 48 V to less than 10 V). Optocoupler U1 has the LED extinguished. This enables timer U2. When the transmitter is activated, tone decoder U4 detects the 100-kHz signal and outputs a low signal, which lights indicator LED1. LED1 is also used to set the transmitter frequency. Also, U2 is triggered. U2 is configured for the latching condition. U2 feeds the base of Q3, turns it on and energizes relay Kl, which switches in the fax machine to the telephone line. U3 prevents U2 from being accidentally triggered by transients on the telephone line. When the phone is lifted off-hook and it resets U2 after about one or two seconds of delay, transients are allowed to subside before U2 is reset, and it waits for a negative pulse on pin 2 to turn on. When U2 turns on, Q3 is biased on, which activates change-over relay K1.
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....
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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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