When the headunit in my car tells me "you must be stopped before being able to perform certain operations", I say "how can we trick the headunit into thinking we are stopped?"

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Status:   Completed

When the stock headunit in my car decided to die and eat the 6 CDs previously loaded into it, I decided to take revenge. My two goals in revenge were: 1) retrieve the digested CDs, and 2) replace the headunit with something better. After a few hours with a screwdriver, step 1 was complete, and I ended up with some sweet components including DC motors outfitted with worm gears! Cool!

After a bit of research, I settled on the Alpine W505 headunit. This was a few years ago, and this headunit was incredible at the time. Even today it is still fantastic for what it can do, but there was one issue – several features were disabled unless the car was stopped and a handshake was performed involving the hand and foot brakes.

This is an easy fix, just needed a power regulator, a lightweight microcontroller, some resistors and capacitors, and two transistors. Here’s a quick schematic of what we need:

Now, this being one of the first projects I created from scratch, I overlooked one important thing when I was making it work. Functionally, it works perfectly – it has worked flawlessly every day for over two years, but it has a side effect

One day after leaving my car for a few days and coming back to a dead battery, I had an “ah-ha!” moment. I realize it’s probably not a good idea to feed a constant +12V signal into the power regulator, because the regulator will constantly be eating power to drop the voltage down to 3.3V.

What I should have done is to only use the +12V Ignition signal to power on the regulator and microcontroller, because then the device would only be able to use power when the Ignition line is powered. I’ll fix this one day when I dust off my PIC programmer..