Adafruit - vehicle input announcement prank

I want to play a prank on my nephew while he is away on holidays. His beloved car is the victim. The plan is to have an abusive comment come from under his dash in response to specific actions he takes. eg, “turn left you moron, not Right” when he flicks his right turn indicator.
I’m assuming the easiest point to take the inputs from will be the actual device, eg. turn signal lamp, electric window switch, reversing lamp, etc. so the signal trigger will be +12V.
I believe the parts i will need are:
Sound file storage and generation - Adafruit Audio FX Sound Board + 2x2W Amp - WAV/OGG Trigger
Step down from 12V to 5V to power the sound board - DC-DC Adjustable Step-down Module 5A 75W
Step down from 12V input to 5V input - 2 x Logic Level Shifter, 4-Channel, Bidirectional
Sound output - Stereo Enclosed Speaker Set - 3W 4 Ohm.

Have I forgotten anything, is there a better way to do this?


Hi Richard,

I wouldn’t recommend making any changes to the car itself if it isn’t your property, this could quite easily slip into vandalism under Section 195 of the Crimes Act 1900 (NSW), and cause issues with the cars insurance or getting the CTP/Green-Slip for the vehicle if the vehicle electronics are modified.

This could also be fairly distracting while driving if it can’t be disabled or if someone who doesn’t know about it is driving (which I imagine would be part of the gambit). It’d also lose it’s comedic effect after the first time it goes off, you’d want to be able to get rid of it pretty easily.

Personally, if you want to go ahead with this, I’d recommend instead putting together a separate piece of hardware like the old Jimmy! What’s that cricket noise project. This was triggered with an LDR, and would just play obnoxious cricket noises occasionally and randomly when the lights were out, making it difficult to find at night as turning the lights on would kill the noise.


You can probably do something similar with a small speaker, battery, microcontroller, and accelerometer/gyro/compass to say obnoxious quips about the acceleration, turning, stopping, etc. without needing to actually make any modifications to the car itself.

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Hi Richard,

I think Bryce has suggested the easier pathway here that’s more likely to result in them taking the joke well.
Half the fun of hiding an obnoxious noisemaker is finding the most creative place to hide it so it takes the victim a while to track down.

Thinkgeek used to make an annoy-a-tron that was designed to be as small as possible so it could be hidden inside other devices, and only make noises occasionally so you had to commit quite a bit of time to finding the thing.
If you’ve spliced into the wiring harness of the car it’s going to be immediately obvious what’s happened whereas an indirect approach using a motion sensor like an accelerometer would mean you could hide the device virtually anywhere.

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Thanks Trent,
I understand the concerns identified by Bryce, and reckon I have a good feel for the pro’s & con’s. I had always intended to make this a bolt on item, that can be switched off at will.

Can you confirm whether the parts that I’d listed in the original post will do the job?

Hi Richard,

Those components should do what you need. I’ve noticed the audio FX board triggers on an active low signal, that is a voltage pulled to ground triggers it. You’ll need to confirm what levels the indicators and lamps in the car use but I suspect it will be active high, since you’re treating power to the device as a signal to switch on.
The name of the circuit to handle this is called an Inverter. So you could add that circuit separately to a regular logic level converter, or find a logic level converter that can also invert the signal for you.

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