Bridging 1 second power gap for Android Auto device, calculating size of capacitor
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19-10-2023 10:24am#1
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Hi.
Just to be clear, a capacitor isn't a battery, so its discharge curve differs significantly. A battery will maintain it's output voltage while a capacitor will drop the voltage very rapidly in line with its charge. This becomes a problem when devices such as the android tablet require a stable input supply of 12v, it only gives you a very small voltage input window to work with.
But this is what I worked out:
I took the resistance of the tablet to be 24ohms (12*0.5A).
So a 1F capacitor would do what you need as the Vdrop in 5 seconds would be only to 9.7v. Except that's a very large capacitance to have on a 12v circuit - you would need a super-capacitor and some protection on the circuit to prevent it pulling too much current from empty.
Have a google for supercapactor power supplies or equivalent 12v UPS's such as these (only cheaper):
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I'm such a fool, what I was looking at provides power for a preset amount of time when power is supplied to it and then switches off.
Your doohickey is the right one, I need to wire a permanent 12 volt from the battery into it (will need separate fuse) and I will take the existing power line that is turned on and off with the ignition as a trigger line. This setup I can then program to keep power going from a few seconds to one hour after I turn the car off.
I cannot make friends with Ali, he wants access to my Facebook or Google and he ain't getting that. I found the same module on eBay.
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OK, the thingy arrived some time ago and I managed to wire it all in over the Christmas.
The best permanent power sauce that runs without interruptions is the horn. I'm also stealing power for the central locking I installed in the car from there. Central locking and the Android screen do not use all that much power, so it "should" be ok.
When I ordered that thing I had the wrong idea about how it worked. It seemed logical to me that you have permanent power, signal power and ground on one side and a switched +/- power outlet on the other side. How wrong I was! Permanent power from the car goes to the + of the thing you want to run and the device switches the - side on and off.
Closer view
Yes, it's messy. But it works.
I can now start the engine and the Android screen won't do a restart. When I shut off the key, it goes off after 5 seconds. I could program a longer or shorter delay if I wanted to.
I have fitted a backup camera, the Android screen, central locking plus boot popper and four new speakers to my car. While I did solder the odd wire, 99% of it was done using crimps. It has made this job SO MUCH easier! Had I done this using just pliers and a soldering iron, I'd still be at it.
The description of the item on Ebay on how to wire it was not making sense to me. Thankfully I found a wiring diagram. As I was wiring it, I kept thinking "this can't be, this doesn't make sense, this is nuts!" but in the end it worked. And worked very well, this now does exactly what I want it to do
My only problem now is that audio from that screen is in mono! Aaaargh! It really hurts my soul to listen to music over that, so I mostly listen to scratchy, crackeldy FM radio. But then I can't hear the sat nav, which is annoying. Does anyone know how I can use Android auto but with the audio coming from the phone's headphone socket?
Post edited by Detritus70 on1 -
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Just to give a final update.
The Android Auto screen I was using turned out to be mono only. I contacted the manufacturer just to ask them to confirm or deny that fact to me. The resulting conversation in Chenglish consisted of nothing but incomprehensible gibberish from Hodozzy.
They offered me €60 if I write a 5 star review, which I did and I promptly received €70 back to my account. Not Amazon vouchers or some other form of credit, actual, usable money. I did mention that the device is mono in my review.
I then ordered the device you see in the attached picture and it is stereo, works better and has good sound quality.
Funny thing, this second screen got lost in transit by Amazon and I got a full refund. And later on I received a phonecall from someone in our village and they actually had my package!
So I got a 50% refund on my original screen and a second one for free. So all in all that worked out pretty well for me. The new screen has exactly the same connections as the old one, so it dropped right in.
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