For my high school class's senior prank, we'd like to buy cheap prepaid cell phones (like these: http://bit.ly/VSqOk3), hide them in the ceiling tiles, and then call then randomly throughout the day. However this gets expensive quickly. Is there a cheaper way to build or buy something with similar functionality? It doesn't necessarily even need to be remote controlled if it could be programmed to go off at certain times.
Cheapest way to build or buy a remote controlled sound maker
devicesound
Related Solutions
This piezo buzzer is rated for 3 V operation and produces 100 dBA at 10 cm, which is 80 dBA at 1 m, and 60 dBA at 10 m.
Maximum current is 9 mA, so if you would give one 100 ms burst every 10 seconds your battery will last 4 months.
A piezo speaker (Piezoelectric Transducer) is most likely what your looking for. They are quite cheap, usually around $1, and small! There are also many other alternatives, take a look at Loudspeaker Drivers Wiki.
You could even try to make your own, not that I would recommend it. How to make your own piezoelectric speaker.
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Best Answer
simulate this circuit – Schematic created using CircuitLab
Assuming you buy about 25 of each:
An Attiny is about $1. A small speaker is about $2. A MOSFET to drive it is about $0.25. A small 3.7V LiPo battery is about $2. The Atmega can run on the built-in ceramic resonator at 1 MHz or 8 MHz when fed 3V or better. 1 MHz (and perhaps sleep mode) will extend the lifetime, although you'll likely get a couple of days of battery life even without that.
http://www.digikey.com/product-detail/en/ATTINY85-20PU/ATTINY85-20PU-ND/735469 http://www.digikey.com/product-detail/en/2403%20260%2000031/423-1172-1-ND/3854653 http://www.digikey.com/product-detail/en/BS170/BS170-ND/244280 http://www.hobbypartz.com/250mah.html
The Attiny can be programmed to wait for a random amount of time, and then make a noise on the output pin that drives the MOSFET/speaker. You'll need a USB programmer and a socket to program the chips in, which adds about $10 of one-time cost.
http://www.amazon.com/SainSmart-Programmer-ATMEL-ATMega-ATTiny/dp/B0051SRZWC
plus a breadboard and some jumper wires for programming.