This version of the Link is for those who really need a good cheap intercom that will work reliably, but without access to an outside Telco line. This could be in a pre school, a hobby farm or a small workshop or factory, where external phone traffic needs to be kept separate and protected from phone abusers and kids playing aroundG It follow
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s mainly the principals of the Link pulse dial circuit, but with the modifications and additions of the Link A2B+1 for DTMF dialing. Basically what IG ™ve done is remove the OSL relay and the flip flop (FF2) that controlled its activation and release, and added an extra two internal handsets and their associated relays and components. FF1 (as part of the Ring Trip Circuit or RTC) is still there, but is now shown down the bottom of the diagram for simplicityG ™s sake. Internal wiring for the RTR relay is as per the Link A2B circuit. When any phone is picked up off hook and a number from 1 to 4 on the keypad is pressed, the DTMF decoder chip (IC2) decodes this into IC3 (1 x 16 decoder) and the output of IC3 is then fed to the appropriate base resistor of Q1 to Q4 (R11 through R14). Pin 11 of IC3 goes low, removing the high from pins 12 and 8 of IC1 and impulsing of the selected line relay (LR1 to LR4) begins, via driver transistor Q5 and the appropriate buffer transistor (Q1 to Q4). When the called party answers the call, the RTC circuit G tripsG ™ the ring current, impulsing along with the ring tone is halted, and the conversation can proceed. When the conversation is completed and both phones are hung up, the collector of OC1G ™s phototransistor goes high and resets both FF1 and IC3. Pin 11 of IC3 goes high again, halting the impulsing action of IC1 but providing dial tone from pin 5 in the reset state, ready for the next...
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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