Lamp signaler with wire control
This project is the first experience of the circuit category of communications.
For many experimenters, that is the most interesting type of circuit, because you have an overview of the radio, telephone, light and other forms of operation of electronic communications circuits over long distances.
This project is a lamp to signal transmitter wire with control. Control is the 3-volt lamp that lights up to indicate that the other signal LED, which can be at the other end of a long line, is on.
The signal lamp apparatus is the LED. A transistor is used to turn the LED on.
When the key is closed, this complete two circuits of 3 volts. A circuit feeds the 3 volt lamp and lights. The other circuit provides the base bias of the switching transistor through the dropping resistor of 1 K.
The control 50K is used to adjust the polarization to a level which allows the transistor to turn on but no more than do. The reason for this is to prevent any tension which might be induced on the long transmission line to the transistor and also the LED on.
This demonstrates the operating principle, but of course, the 3-volt lamp with its strong current would not be used for actual circuit for a long transmission line.