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Sound alarm control unit
This module was part of the rack box project — which was terminated when I moved out of my first apartment.

Simple unit to control three sound signals; beep, siren and buzzer. Uses an AVR ATtiny2313 microcontroller.
Details
This simple unit controls three sound signals; beep, siren and buzzer. Each sound signal will only be given once when a new alarm is triggered, the input must remain clear for at least four seconds for that signal to rearm. A beep is given every six minutes if an alarm is active, as a reminder. The sound LED flashes when a sound alarm is active; once for signal 1 (beep), twice for signal 2 (siren) and three times for signal 3 (buzzer), this flashing pattern is repeated.
SSU used to control the sound alarms in the Rack box. Modules that had alarm outputs sent a signal to SSU, which carried out the sound alarm. If system mute was active the power to the buzzer and siren was disconnected.
Signals
- 100 ms siren
- One second siren
- Three seconds buzzer
I/O
Inputs
- Signal: Beep
- Signal: Siren pulse
- Signal: Buzzer pulse
Outputs
- Siren
- Buzzer
- Sound LED
- Lifesignal (to Module stability monitoring unit 2)
D-Sub 9-pin
- 0v
- 5v
- Signal: Beep
- Signal: Siren pulse
- Signal: Buzzer pulse
- Siren
- Buzzer
- Sound LED
- Lifesignal
Source code

https://github.com/thomasjsn/AVR-Sound-alarm-controller
Gallery
SSU installed in the Rack box
Schematic drawing
Parts list
Qty. | Part |
---|---|
1 × | AVR ATtiny2313-20PU, DIL-20, 20 MHz, 18 I/Os |
1 × | Capacitor, aluminium electrolytic, 10 µF, 25V |
1 × | Capacitor, ceramic, 1 nF, 100V |
1 × | D-sub soldering cups, 9 pin male |
1 × | DIL socket, 20-pin, 7.62mm |
1 × | Enclosure, plastic (1591 FL), 100x50x25mm, flange |
1 × | LED 5mm coloured clear, Green, 2.1V, 20mA, 30mcd, 10° |
1 × | LED 5mm coloured clear, Yellow, 2.0V, 20mA, 40mcd, 10° |
2 × | LED holder 5mm, RTC51, black plastic |
32 cm2 | PCB, stripboard, 100x160mm, 160cm2 |
5 × | Resistor, carbon film, 0.25W, 330 Ω, 5% |
5 × | Resistor, carbon film, 0.25W, 4.7 kΩ, 5% |
3 × | Resistor, carbon film, 0.25W, 10 kΩ, 5% |
4 × | Transistor, NPN, 100 mA, 45V, 0.5W, BC547B |