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Let me ask this simply, then explain my use case below. This is a Easy Line Activated Solid State Switch Project . Each and every time a phone on the same line or calling numberis taken off-hook, the circuit will be activated to control an external electronic circuit. If several extension telephones are used on one phone line, the circuit can be useful as a busy indicator. LEDl contains a special flashing red LED that makes an excellent indicator for a busy circuit condition.   Line Activated Solid State Switch Project Circuit Diagram The solid-state switch can be used for several other phone-activated applications, such as automatically turning on a cassette recorder, starting a phone-use timer or counter, etc. A small relay can be connected at points A and B, in place of LEDl, to control external circuits. A 117-Vac-to-6-Vdc plug-in power supply can be substituted for the battery to keep the operating cost at a minimum.  The 48-Vdc, on-hook, phone-line voltage keeps Ql...

This is a circuit for emergency lighting with LEDs that uses electricity from the telephone line . Generally the phone line has a DC voltage 48V and somewhere around 20 mA , and when the phone rings , the voltage rises to 96V AC . This works in a way that the phone line will not be busy while the LEDs are turned on and when you pick up the phone , the light goes off and lets you use your phone normally .  Emergency Light using Phone Line Circuit Diagram

Line Follower Robot Sensor Concept - Sensor line detector is used in line follower robot is usually based on the principle of light reflectionto distinguish the line with the background color. In the dark color of the light absorption is greater than that of white light reflected to the sensor becomes smaller. Position sensor to track the trajectory and the example circuit. Line Follower Robot  Sensor  Concept Light used for the introduction of the line is usually visible light and infra-red. Sensors for visible light are commonly used are LDR (Light Depending Resistance), while for the infrared light is atransistor and photo diode (photodiode). Sensors placed at the bottom of the frame to hang the robot, so that its position can be located just above the track to be read.

This circuit takes two separate line-level stereo (L & R) signals and combines them into one stereo (L & R) output, thus avoiding the need to switch between two pairs of input signals. In the author’s application, it is used to feed the stereo audio from a TV receiver and a DVD player into an external amplifier. The need for the circuit arose because of a design peculiarity in the TV receiver. The TV has four A/V inputs and one A/V output. AV1-AV3 accept composite or S-video plus stereo audio inputs and these feed into the TV’s A/V output. AV4 accepts Component video (Y/Pb/Pr) plus stereo audio but unlike AV1-AV3, its audio (and video) signals are not fed to the TV A/V output. The Y/Pb/Pr input was chosen for use with the DVD player because of its superior video quality, while the audio was to be fed to an external amplifier for improved reproduction. Circuit diagram: Dual Input-Combining Stereo Line Amplifier Circuit Diagram However, manual switching was inconvenient, henc...

Circuit Diagram  Description   If you feel that somebody is tampering with your telephone line you might find this little circuit useful. It detects if there is another telephone connected to the line, if there is a short or an open line. Sound and a flashing light will tell you which is the current situation. The speaker is practically cut out during a normal conversation thus preserving privacy, only the LED will flash occasionally. The circuit does not require any battery and takes the supply from the telephone line itself. The transistors used are wired in a reversed biased fashion thus behaving as oscillators. You might try the 2N2222A as an alternative (not tested). This monitor is, of course, suitable only for analogue lines. Watch the polarity of the input line: the circuit will not be damaged by a polarity reversal but it will not operate correctly.  Author : smartkit Source http://www.electronics-lab.com/

This small and bright LED lamp is telephone line powered, means it uses the power of our telephone line. There are about -40v to -50v at telephone line, LM317T is used to adjust them according to our demand. 12 white LEDs of 5mm dia is used in this lamp, are all in series to compensate the voltage. Out of four wires of telephone only red and green is of our interest. This telephone line powered LED lamp is small, efficient and bright; one can also be use this for study or desk lamp. Schematic: Telephone Line Operated LED Lamp Components Required: BR2----------------------Bridge Rectifire U2------------------------LM617T or LM317L R3-------------------------270 ohm 1/2watt R4-------------------------6.8k ohm 12 white LEDs