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Sound alarm control unit

From CaveLab
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This module was part of the rack box project — which was terminated when I moved out of my first apartment.
SSU installed in the Rack box

Simple unit to control three sound signals; beep, siren and buzzer. Uses an AVR ATtiny2313 microcontroller.


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.


  1. 100 ms siren
  2. One second siren
  3. Three seconds buzzer



  1. Signal: Beep
  2. Signal: Siren pulse
  3. Signal: Buzzer pulse


  1. Siren
  2. Buzzer
  3. Sound LED
  4. Lifesignal (to Module stability monitoring unit 2)

D-Sub 9-pin

  1. 0v
  2. 5v
  3. Signal: Beep
  4. Signal: Siren pulse
  5. Signal: Buzzer pulse
  6. Siren
  7. Buzzer
  8. Sound LED
  9. Lifesignal

Source code

Bascom-AVR source is available in a git repository:


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