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Mint Tin Personal Alarm

Finished Alarm

Combine a mint tin, piezo siren and some basic components into a personal alarm that's both functional and visually pleasing. This design involves connecting a 12 volt A23 battery to a piezo siren through a toggle switch and a tact switch. The toggle switch is used to arm the device (preventing accidental activation) and the tact switch activates it.

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Materials:

  • Mint Tin. The dimensions of my tin are 40mm x 77mm x 22mm.
  • Mini piezo siren capable of being run by a 12v power source.
  • A23 12v battery and holder
  • Toggle switch
  • Tact switch or other momentary on switch
  • Red 5mm LED and a resistor exceeding 500ohms*. I used a 620 ohm resistor

* Resistor value calculated for a 2v 20ma LED

Components

Tools:

  • Soldering equipment
  • Small pliers and other basic hardware
  • Drill
  • Hot glue gun

So you can measure your components and determine their placement within the tin, they need to be prepared for installation. This involves disassembling your piezo alarm and adding the resistor to your LED.

Piezo Alarm Disassembled

My piezo alarm required removing two screws located on the back. The speaker could then be pried free with a flat head screwdriver and the circuit board removed with a pair of pliers. I also extended the speakers wiring to make it easier to work with when installing into the tin later on.

The LEDs legs were bent flat against the base and the resistor added to the positive leg. It doesn't matter which side you add the resistor to as long as you note which leg is the positive and negative.

Holes Drilled

We need holes for both switches, the LED and the speaker. It may be a tight squeeze fitting all your components into the tin so be sure to measure them and calculate where they can be located without obstructing one another. The placement shown in the image worked for the components I used. The bulkier toggle switch is located at the base of the tin and the smaller tact switch closest to the lid, allowing the battery to fit into the top portion of the tin so you can replace it down the track.

Apply masking tape to the tin to easily mark the holes with a pencil. I also placed the tin on paper towel while drilling to prevent scratching.

Completed Circuit

Connect up all the components as per the wiring diagram provided. I used 10cm lengths of hookup wire which allows some wire to play with when installing everything into the tin but not so much that you will have difficulty stuffing it all in there.

Simple Circuit Diagram

Once you've got it all together, test your setup by installing the A23 battery into it's holder. The LED should light up once the toggle switch is activated and only allow the alarm to sound when the device is armed. Now you've confirmed it's working, you can move on to assembling the alarm.

Battery Compartment

This part will take some patience but given time, a steady hand and a cold drink you'll have it installed. Your mileage may vary depending on the parts used and their size but this worked for me. Hot glue the circuitry of the alarm to the base of the tin. The toggle switch is then installed using pliers, followed by the LED and the tact switch. Be generous with the hot glue to ensure everything stays put. The speaker is then pushed into place, don't be concerned if it doesn't line up perfectly with the holes drilled. The battery and holder is then installed in the top of the tin facing upward to allow the user to replace the battery if need be.

Pair of Alarms

The lid on my tin wouldn't close properly and required I give one side a trim with a dremel. That's it! You should now have a functioning personal alarm. Test that it works correctly and roam the streets with the knowledge you can make a lot of noise should someone cause you trouble.