Is it possible to design a small / compact, hand-held siren (i.e. with a loud hooter), that is battery powered and fits into something like a 3"x3"x2" box ?
The requirements in more detail:
Hooter that is small, yet loud enough (not sure in decibel level terms, but something similar to what one finds in Residential Intruder Alarm systems).
Can operate off battery power (e.g. 2-3x 1.5VDC AAA cells) s.t. a. Hooter can sound a pattern for about 10minutes b. While circuit, which includes a NO/NC latching push-button switch, requiring "push" detection, can operate for few weeks (if not months).
The conflicting design constraints in my mind are:
- Small / cramped space that this whole thing needs to fit into
- Hooter loudness and duration required (knowing that these things draw a lot of current, and typically operate on 12VDC)
- Everything running off small (size and number of) battery pack.
The requirement of few AAA's instead of say LiPO is to keep the cost as low as possible, and keep things simple (i.e. to the extent I can deal with electronics).
Happy to elaborate and clarify, and very happy to have alternative suggestions. Note that the use case is, someone presses a big-round button (not sure what it is called, but the type you find in lifts, and in industrial controls that start/stop conveyor belts etc.), on a small hand-held box (no wires, self-powered), when they are in distress, and it makes a hell-raising racket to draw attention.
Answer
The amount of "loudness" you need is uncertain. but you can almost certainly get more than enough power from say 6 x AA cells and a Piezo sounder.
Ignoring your battery spec for the moment.
6 x 2500mAh AA Alkaline have about N x V x C = 6 x 1.2 x 2.5 = 16.5 Watt hours capacity. For rapid discharge lets allow 5 to 10 Watt hours.
10 minutes operation at even 5 Watt hours is 20 Watts input. That is vastly more power than you need and gives a sensibility check on the battery size.
6 x AA cells
= 6 x 14500
= 6 x 14mm dia x 50mm long
= about 30mmm x 45mm x 50mm envelope
= easily inside size spec.
6 x AAA give around half that
3 x AAA give around 1/4 that or say 1 to 4 Watt hours energy or maybe 5 Watts siren power.
Piezo sounders are relatively flat and available in as powerful as required sizes. Good acoustic coupling to the housing used is probably your main area of effort.
Electronics volume need is minimal
Fewer cells - lower voltage = harder to get power out. 6 x AAA = 9V start = 6V finish, when driving a piezo push pull give ~18V down to ~12V peak to peak output voltage.
A switch mode voltage booster MAY be needed. Component cost under $1 in manufacturing volumes.
**All the following are available from Digikey:
Mallory Sonaalert - 105 dBA at one metre.Just apply DC and go. And similar
Probably too low powered. Mybe not
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