DC current (Battery) is needed by the carbon transmitter to make the phone work. The way the telephone company does things is to feed battery to a telephone line using a device that allows the DC (Direct Current) to flow but does not short out the AC (Alternating Current) or voice as it is called in telephony. The voice can also be called the a
Click here to download the full size of the above Circuit.
udio, the talk path or speech. An inductor in telephone work is a coil of wire with an iron core. This has Impedance on AC. If you took several nails and put 200 feet of copper over them, like maybe you did in school and made an electromagnet, several principles apply. If you connect this to a battery, you get a magnet and current flows from the battery. If you took a meter and measure the DC resistance it might be 10 Ohms. But if you used this same coil on AC it has both resistance and reactance (this is going to get complicated, you might want to skip this section until you get your electrical engineering degree or you read that AT&T book) and this combination is called Impedance. A wild guess would say that at the power line frequency this might be 40 Ohms. If you used this at voice frequencies, to feed battery to a telephone circuit that Impedance might rise to 200 Ohms. A Telephone has an impedance of between 600 and 900 Ohms. To feed battery you need an inductor that allows DC to flow, typically about 35 milliamps (. 035 Amps), and has an impedance of several times the impedance of the telephone so as to allow the voice (audio or speech) to be unaffected. For a coil this means about 5, 000 Ohms impedance or more at voice frequencies. For you engineering types, the line losses (cable resistance and such) must also be considered but I am going to leave much of this out of the discussion. I am also not going to cover...
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.....
characters left: