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Intercom opened by Morse code

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Vermes

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This is a project of intercom opened by Morse code. It was inspired by situations, when it was difficult to open door because both hands were busy, keys were lost somewhere or left at home.
„Dialing” proper sequence of short and long signals is to enter electric strike for a few seconds.

How it works:
The system receives pulses (tone melody) from CA line, which are recognized by MCU. It counts their duration and on that basis, determines the correctness and the type of entered symbol (dot/dash).
  • pulse ≦ 0,3s – dot
  • pulse > 0,3s and ≦ 1s – dash
  • no pulse during 1,5s – checking the entered code

The system is connected to the microphone line, so it informs the caller of any errors by beeps:
  • 1 low beep – button held down for too long
  • 2 low beeps – incorrect code
  • 3 low beeps – too long code

Errors are reported from the second entered symbol so they do not confuse the unaware caller who usually calls once.

When the code is entered properly, 4 high beeps will be heard and the electric strike will be released for 3 seconds.

Electronics:



The device uses an existing uniphone with 6-wire installation. Attiny2313 MCU with additional electronics is placed on a separate, small board. It is connected to the terminals of the original board of the intercom by few wires. The intercom board does not require any modification.

Input:
When the button on intercom is pressed, the CA line charges a small capacitor C1. Zener diode limits the voltage to 5V (the melody has a greater amplitude). The capacitor provides the exchange of modulated melody to logic 1 or 0.

Outputs:
The microphone line is shorted by the transistor. Its base is controlled by one of the MCU pins using PWM signal, generating sounds in that way. Serial resistor 10k provides reasonable level of the signals volume.
Electric strike is connected to the triac, and the triac is connected to the optotriac, controlled by MCU port.

Power supply:
The system asleep consumes 10mA (8mA 7805 + 2mA Attiny). This can be reduced. During the operation of opening the lock, it consumed >20mA, so it is impossible to power it from microphone line or electric strike. That is the reason why external power supply has to be applied. The intercom is connected to the power supply from the router, which does not read the additional 20mA.

Video:


Link to original thread (useful attachment) – Domofon otwierany kodem Morse'a
 

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