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Topic: car alarm with MP3 sound (Read 1 time) previous topic - next topic


I have a idea to hook a car alarm up to a UNO R3 with a mp3 shield from sparkfun.com part #10628. I am not sure if this work. Most alarms make a chirp for arming and two chirps for disarming. Can i use the speaker output from the alarm system to signal a certain Mp3 to play from the UNO? I would use a 1 second clip Mp3 for the single and double chirp signal and i could use a longer Mp3 for the constant signal for the main alarm sound. The idea that i have is to run the speaker wire from the alarm to the UNO with a voltage regulator then run the sound output from the UNO to a amp then to the speaker. Follow that? Is there a better way?




What you're suggesting is feasible, but rather than a voltage regulator you'll probably want a voltage divider sized to suit the maximum voltage you measure during a chirp.  A voltage regulator will shape a voltage higher than 5V down to 5V but a divider constructed from a pair of resistors will be cheaper.  Then teach your Uno to look for the voltage changes, likely using an interrupt on an input pin.  You might also look to the confirmation that flashes the indicators/hazards on the car since at least you know that should be a 12V trigger that you can voltage divide down to 5V for the Uno input quite simply.  Or maybe tap into the line that runs to the flashing LED on the dash?  Lots of options  :)

You might want to check how loud that shield is first though, depending where you're mounting this.

Cheers  ! Geoff
"There is no problem so bad you can't make it worse" - retired astronaut Chris Hadfield


Using a voltage regulator like that is bad. It is slow and not very stable, it is not what they were designed for.
You can use a potential divider as described above but you can also use a series resistor of about 220R and a 5.1V zenner diode to protect your arduino's input.

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