Alarm siren, 12 V
A 12 V electronic alarm siren with its own oscillator: DC across it and it wails, drawing about 300 mA.
Aliases: siren, alarm siren, 12 V horn, burglar alarm siren, sounder, loud buzzer. Like the active buzzer it is a polarized load with the tone made inside, only it wants 6 to 12 V and far more current.
Pins
| Pin | What it does |
|---|---|
+ |
The red wire, to the supply side. |
- |
The black wire. |
Wiring it to an Arduino
A pin cannot give 12 V or 300 mA, so the siren hangs off a logic-level MOSFET
(a D4184 module, or an IRLZ44N with the siren from 12 V to its drain), a
TIP120, or a relay, on a 12 V supply of its own whose minus meets the board's
ground. Then digitalWrite(pin, HIGH) sounds it.
Properties
| Property | What it sets |
|---|---|
voltage |
The rated voltage, 12 V. |
current |
The current at that voltage, 0.3 A: the listings give 100 to 350 mA. |
sound_from |
The voltage across it under which it is silent, 6 V. |
While it runs
Rings pulse out of the horn while it sounds.
What the model gets right
It needs its voltage. A board's 5 V rail is under its 6 V, so it stays silent, which is the usual surprise.
It loads the supply. It draws current at its rated voltage, as a resistor.
Polarity. Reversed, it passes nothing.
What it does not model
The sound: Mokxi plays no audio except the multimeter's beeper, so the siren shows that it sounds rather than making noise. Its 110 dB, its two-tone or wailing sweep and how much quieter it is at 6 V are not modeled, and a real siren's current changes less with the supply than a resistor's does.
Common mistakes
Running it from the board's 5 V pin: too few volts and too much current.
Forgetting to join the 12 V supply's minus to the board's ground.
See it in action
Motion alarm siren sounds it for ten seconds when a PIR sees someone. Open it at /templates.