Good day, I hope this is the right place to ask this question.

To provide context: A few days ago I found an old Sony Ericsson W205a Phone, it can be used to speak and receive text-messages, but it's unable to reproduce any sounds unless external speakrs (through headphones/usb/bluetooth) are used. I tried with my car radio (that has bluetooth), and it works perfectly fine with it.

However, I keep on forgetting to turn the cellphone ON every-time I get on the car, making it's presence there kind of useless. Leaving it always ON would be a good solution, but the idea of wasting electricity in something I am not using makes me feel bad.

The question: I am kind illiterate in what regards electrical engineering (I'm actually a programmer), but is there any way to modify my SEW205a to turn ON when receiving electrical current (coming from the car), and OFF after 10/15 minutes of complete inactivity? Do you think there is an easy way around this, or is the task is so hard that's beyond my skills?

Thank you.


I recommend leaving the phone on a cig lighter charger in the car if your cigarette lighter is powered all the time. The phone should use very little current when the phone battery is fully charged. You can check this by measuring the current the cigarette lighter takes. It should be less than 20 milliamps from the 12V supply. It would not drain your battery under normal conditions (driving once a week at least).

Here is why I not recommend modifying the phone: Opening the cellphone and wiring something to the On/Off button can cause more trouble than good, the phones are densely packed and you'd also need to design and build a custom piece of electronics to operate the button contacts. Probably not the best investment of time.

Either way, the calls made to the phone will goto the voicemail when you are not in the car - either because it's off or no one pick it up.

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