The circuit was designed to provide a monitoring scheme for a telephone line where several phones are installed, to indicate when one is being used. 4N25 – a general purpose optocoupler that consists ...

The circuit aims to create a recording scheme not only for spying but for business purposes where conversations are noted for future reference. 4N28 – a general purpose optocoupler that consists of a ...

THE best method of testing telephone circuits and apparatus is a problem to which a great deal of attention has been devoted of recent years. Speech is carried over a telephone circuit by means of ...

Today when we send information -- speech, words, numbers, or pictures -- to someone far away we can use the radio, telephone, television, fax machine, or a computer network. However, the need for ...