Voicemail capacility (although not implemented, there are four ADCs that can be used to sample and record the phone audio) A storage volume (SD card) would need to be connected. This project was inspired by these other homemade exchanges: Markus Wandel and Andrew Holme. My project is not a kit, not from instructions, and not a copy of the
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above people`s designs. I actually designed and am building all of it from scratch using parts I own and parts I could obtain. Power Supply box: Conatins a 60VDC power supply that will be used to generate high voltage 20Hz AC ringing. Also contains a 7VAC transformer for 5VDC. Fuses and switches. Talk Supply filtering: A salvages switching power supply provides 42VDC for phone talking current. This supply is noisy so extensive filtering is used. Here, and inductor (really half a transformer) and a capacitor remove some of the noise. The rest is filtered out on the main board using RC low pass filters set to 2. 34 Hz. Atmel AVR Atmega328 microcontroller. This chip handles all tone generation with the help of a DAC chip to the right. These two parts generate all busy, dial, and ringing tones by reading WAV files stored in the flash memeory of the AVR. The AVR also plays DTMF tones to the outside line to dial on it. The AVR is overclocked to 25Mhz so it has enough time to transfer data over a serial shift register interface to the DACs. MT8870 DTMF decoder. There is one of these and associated circuitry for each extension. The DTMF chip is connected through a four bit data bus shared among the other DTMF chips with CS lines to select what chip is being read. The Std (tone detect) pin is connected to the Atmega644 so it can wait for digits, select the MT8870 where the signal originated, and read off a four bit code refering to...
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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