Classical scheme of intercom system
Together with doorbells almost every building consisting of more than one floor there is built an intercom system. Currently the market offers advanced digital intercom systems in which electronic occupies a significant part. Each company offers its products and respectively provides diagrams and installation schemes.
Кey elements of which are built a classical intercom installation are carbon microphone (M) electro dynamic speaker (T) and power supply. This is one of the first circuits created and serves more to explain the principle of design of the intercom, but is fully operational.
Upon impact of sound pressure (speech) on the carbon microphone diaphragm (1) , it begins to vibrate In synchrony with these vibrations the clamping force of the carbonaceous grains (2) are changing , thereby changing the electrical resistance between the electrodes (3) and (4). When constant voltage U0 ( in the case 8V) is applied, the current through the microphone also is changing. If the microphone is incorporated into the primary coil of the transformer Tr , then in the ends of the secondary coil an AC voltage occurs , the shape of which corresponds to the sound pressure acting on the diaphragm of the carbon microphone.
Doorphones and bells
1.Design of audio and video doorphones with capabilities to open outside door.
2.Desig of bell instalations