This Intercom is powered by two 9volt batteries and uses only current when the Intercom is used.
Both units are connected via a two-wire little cable or simply two wires (dotted lines). The loud speakers act both
as loudspeaker and as a microphone. When you press S1 and speak into the loudspeaker then this signal is amplified
by the transistor stage and made audible in the right loudspeaker and vice-versa. An added benefit of this system is
that when the switch is pressed it is quiet, not even annoying noise. This circuit has worked for me to my full
satisfaction for many years now.
Click here to download the full size of the above Circuit.
I get regular emails with complaints that there is no audio output when the button is pressed. As it turns out, the
problem is always that a low-impedance loud speaker is used and although the circuit is working normally there is no
audio or very little. Indeed it maybe difficult sometimes to obtain high-impedance loudspeakers, which probably is that
by modern radio's the final audio stage is a transistor amplifier and they can provide a lot more current than a tube. To accommodate those in that situation, below is a solution which will solve the problem by using a audio transformer
with a ration of 1:2 or 1:4 to 'up' the impedance. What that means is that the ohm's value at the primary side of this
transformer is about 82 ohms. That will accomodate about 100mA max and because the collector voltage is pretty 'nil',
it is impossible for the transistor to get hot. If it does, you have the incorrect transformer!
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....
Many times for various reasons we forget or can not water the plants that we have in our homes. And many humidity sensors units just notify us with a beeping sound or with a flashing light, that the pot needs watering. But what if we are away from home? This....
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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