Car voltage monitor

Other Hardware Home Automation
1

I'm thinking of making a device that monitors car battery voltage and alerts me if it goes below a certain level, because multiple times I've left the headlights or ceiling light on and the battery was drained.

My vague plan would be an Arduino with a Wifi shield. It would be powered by a rechargeable battery that only recharges when the car is on, so that the Arduino doesn't drain the car battery. I was thinking to do a voltage divider from the car into an analog pin to read the voltage, then email me if it's below a certain level.

I was worried about the current constantly going through the voltage divider (something like 10k ohms) being enough to drain the battery. It'd be preferable if the Arduino could only measure the voltage like once every half hour.

Writing this out, I realize now I can use a transistor or relay on the car voltage wire.

Are there any other things I should consider, or suggestions to improve this idea?

2

The load even an always on Arduino presents to a car battery is minimal. Left for weeks, yes, but overnight or a day or two, nah. Especially if you go to sleep between samples. Put the WIFI on a relay so it doesn't power up unless the Arduino wants to send an alert.

3

Oh good to know, thanks.

4

how far away from your property do you park you car? i.e. does the property WiFi signal cover the area?
assuming your car is covered which WiFi board were you considering? e.g.ESP32, ESP8266, ?
what will be the receiver and how will it alert you?

5

So do some sums.

You can use divider of say 47K + 10K to read the voltage.

At 12V that divider would consume 12/57,000 = 210uA.

So a 50Ahr car battery would drain to 50% in 50/0.00021 = 119,095 hours == 13.5 years.

6

Hi, @pleevamo
If you have WiFi, why can't you get the system to warn you that you have left any lights on, then you save having a depleted battery.

Tom... :smiley: :+1: :coffee: :australia:

7

Or better yet have the Arduino turn the lights off automatically. you could also mount an echo range module in a baggie behind the grill as a parking aid.

A simple time delay relay could insure your lights are off withou anything else.

8

It's parked on the street, and I have a Wifi extender that I was thinking to plug in to the front of the house.

I haven't researched wifi boards, so I'm not sure. Cheapest one that works, I guess. Same with the Arduino.

I don't know how hard it is to do, but I was thinking it would use Wifi to send me an email.

9

I'd read somewhere that the more resistance before the analog pin, the less accurate it will be. Maybe that's not true.

10

That might be a better idea. I'd have to find a way to connect to both the headlight wire and the ceiling light wire.

11

That might work too.

If I'm doing all this work already, maybe I should just try to fix the thing in the car that's supposed to sound a tone if the headlights are on and the car is off and the door is open. It works like 5% of the time.

12

A 10K input impedance seems good enough.

And if your taht woroed about accuracy, do remember to calibrate the Arduino.

13

have a look at arduino-send-email
look at microcontroller with built in WiFi such as the ESP32 and ESP8266 - you can use the Arduino IDE, libraries, etc to program these

14

Noted, thanks.

15

Oh cool, that'd be much more convenient.

16

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