So I'm putting an Arduino in my car as an alarm system, and figured I'd make an audio system as well

So I'm putting an Arduino in my car as an alarm system, and figured I'd make an audio system as well.

I was thinking of using a raspberry Pi, but then I figured if I used an Android phone, I'd have GPS tracking, maps, and voice commands using the software already on the phone, and it won't cost much more, in fact, it's almost the same price as a pi with a small LCD screen and a battery pack.

What does Jow Forums think? Raspberry Pi, or an el-cheapo tablet? If I used the android thing though, I'd have to program it to stop charging when the battery is full, and start when it's down to like 20%, whereas if I used the pi, I'd get a deep cycle lead acid battery that can run on constant charge

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spend an extra $1 or so on a TP4056 to stop it from overcharging if you don't already plan on it

The problem is that Lithium batteries are designed to be charged and discharged regularly. If it holds a charge too long, it starts swelling, and if it's discharged too far, it'll lose cycles regularly too. Never had one of those. It says "charge/discharge protection" so does that mean it'll charge and discharge at regular intervals, or just keep charging until full then trickle charge once full?

Trickle charge I think. I'm not entirely certain

Ah well. If it's trickle charge, I can just use a voltage regulator with the Arduino and the cars battery to step down from 12v to 5v, and use that to charge using the things existing USB port. They usually have built in trickle charge components for those people who leave their phones on charge while they sleep

Why aren't you just hooking up your tablet to the car's battery?
Or are you planning on having it replace your Arduino, and running all the time?

I wanna have it running all the time, so that if the car is stolen, I can track it using the GPS in the car even when it's turned off.

When the car is off, that is

Then you need it to have mobile internet too?

Yeah, but if it's an Android phone or tablet, that won't be much of a problem. 1 gig a month at most should be enough, and that's not much of a monthly cost (think it'll work out to like 10 dollars a month in my country)

You might need an arduino or similar for your alarm requirements and other cool stuff to add later

With both options, android mobile or raspberry pi

RaspPi allows you to do low level shit directly.

There's a few tricks you could do with the Android tablet and its audio jack but that's of course much more limited.

Well in theory you could write an Android app to interface with the Arduino via USB com port, couldn't you?

As far as I know you should not rely entirely in GPIO pins in the rbpi due to its current limit per pin. If you are fine with adding these extra circuits and protections, go ahead. The same for android.

The same is true for an Arduino.

Yes as a usb host. Even bluetooth...

>The same is true for an Arduino.
The raspberry pi still being more fragile tha the arduino.

But why not just use relays? Both Arduino and Pi output pins are meant more for signal rather than full application anyway

Well also consider that some module might need 5V, which is the logic voltage of most arduino, raspberry uses 3.3V, you might need a logical voltage converter. Aka. Extra hardware.

Well yeah, but dirt cheap hardware. Use the standard 5v or 3.3v output from the Arduino or Pi as a signal for the voltage regulator, which literally costs like 5 cents

In general, it's not a good idea to run the Arduino directly on bigger hardware, it's always better to just run it as a signal control center to keep it from blowing

Indeed, I'm just suggesting a way of setup that can be robust for OP's project as I learned studying Mechatronics.

Wow, lots of replies...

Ok so here's my plan: spend 100 dollars on the whole project. Right now, I have an Arduino r3, and a couple of Arduino mini 3.3v. I'll only be using the r3 though, because it can take a 12v input, so I can just plug it straight into the cars battery and have it on constantly that way (also, it takes very little power, so I don't need to worry about having a dead battery if I don't drive for a couple of days).

I can get an android tablet with 3g for around 90 dollars, but it's very basic and I don't know if it'll do the job. Or I can get a raspberry pi with an LCD and a 12v lead acid battery, and a 3g/GPS module for around 110 dollars total.

In both cases, I'd still have to get a mobile internet package, and in both cases, I'd need to write some code to get it to do everything I want it to do.

My issue is, if I have the android tablet, I'd need to somehow get it to keep discharging and charging. What I was thinking of doing was having the 5v and ground pins from the USB cable on a dpdt relay that's activated by the Arduino, and have the phone send the Arduino a signal to say "hey, my battery is low or full" then the Arduino activates or deactivates the relay. But again, I don't know if that will work or not.

Anyone know if the USB will work without the 5v and ground connections? Just to send data from the android to the Arduino

You need at least a common ground.

Ok so then if I just exclude the 5v pin, and have that on a relay, the phone shouldn't charge... But will it still allow the USB to communicate? Preferably without blowing the USB port

Just get a tablet with a sim slot and call it a day.
You can also take it out when you leave your car so there is less reason for it to be stolen.
Not that anyone is going to steal your shitbox anyways.

Why do you want to stop your phone from charging?
Phones already have smart charge control.

Ah sorry, you probably don't want to drain the starter battery

Having a LiPo battery on high charge constantly (above 90%) is a fire hazard, it swells up over time and eventually explodes.

That too yeah, but it'll take so little power, that won't be much of a problem either. In general, it'll take about 2-3% of a 12v45ah car battery over 24 hours.

Surely there would be some sort of standalone GPS unit that you could get (i.e. a pet tracker) that you could use if you want to know where your car is?

It's not only about tracking the car, it's also having a GPS map system so I don't have to use my cellphone and drain my phone's battery

Make a tutorial please once you are done. I'd be interested in doing somethibg like that but I'm a brainlet.

Will do mate ;-)