Creating a monitoring system for an old car


I am looking to do a simple project where an arduino monitors the systems in my old MGA. What I mean by that is mainly to check that the lightbulbs are not burnt out, main, brakelights, blinkers etc.

I have been googling around and I am thinking the way forward is to check the lack of current.

Any suggestions are appreciated!

Yes, you need to check the presence of a voltage combined with the absence of a current.

Google current sensor ICs. You can get current sensing modules from Banggood et al, which are handy because the components are already mounted on a PCB with a convenient connector.

Each circuit you are sensing will need two ports on the Arduino - one for the voltage, the other for the current. In your code you will run a loop which scans each of the voltage pins in turn, round and round. When a voltage is detected, the software should then check for an output from the associated current sensor. If it is absent, or the wrong value, then sound an alarm.

That's the high level view - there is much detail to be added in the implementation.

When you've got that working, you could than develop the Mk2, which continuously monitors the bulbs by feeding them a very small voltage (not enough to light the bulb) and detecting the small resultant current, which will disappear when the bulb fails.

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For checking headlights that current measuring will lower the light emitted.
I know this has been done using a read contact. Using two counter balancing coils, one for each headlight. When both lights work the resulting magnetic flow will be zero. When one lamp pops the other lamp will create a magnetic field trigger the read contact.

Evidence? Source?

Obviously any inline resistance has that potential, but with a suitable sensor there's no way on earth you'd notice it. The battery voltage varies during use anyway - how much of a problem is that?

And how much of a voltage drop will your "counterbalancing coils" produce? The point is, these coils are themselves current sensors.

I’ve done the coil of wire around a Reed switches and it works very well.

It s a lot of effort for just checking bulbs - given that they fail so rarely you need to be sure your circuit doesn’t fail first !

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Don't use serial resistors for the headlight measuring is the point. Do what can be done to have the best possible illumination.
When the alternator is running the voltage doesn't vary significantly. For the read system select swiches needing as low magnetic field as possible. This reduces the number of turns in the coils. Use as thick wire as needed and us possible.

Actually I don't disagree with that, except to say that a decent current sensor won't produce a significant voltage drop anyway, and it's all nicely convenient as a small plug-in module.

Of course, you can use coils wrapped around reed switches for all the other current sensing points if you want - the end result is the same, but it does seem like unnecessary messing about.

ANYWAY, back to the OP's question... Yes, your approach of detecting the current flow is the right approach, but you'll need to detect the voltage as well so the Arduino can know whether current is "supposed" to be flowing.

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Then there is one of the most common failures in vehicles, bad earth causing feedback.
Best detector there is by eye.

For simple current detector, I used to use a small reed switch and wind a few turns of enamelled copper wire around the body until the switch would activate . This enamelled copper wire needs to be of sufficient size to carry the lamps current without producing any noticable voltage drop.
In most cases a piece of 18awg is sufficient. Reed switch contacts then become the sensor which you can do with whatever you like.
Very handy in places where detection of current is required where very little voltage is present such as r/c glow plugs 1.5v.

The coil of wire around a reed switch was what Honda used in the early 80's for detecting bad bulbs, I doubt they are the only manufacturer using that method.

If you're going to run any new wires all the way to the light bulbs, i think it would be more useful to use photo sensors.
That way you check how well the lights are working (their primary and only function) instead of if they just sink power.
As a bonus you can later add brightness adjustment :stuck_out_tongue:

While you certainly CAN check for a failed bulb it doesnt do anything you cant do by inspection.
A more useful and more interesting project would be to use the arduino to provide additional instrumentation the MGA doesnt have; and you can do that without adding a LOT of additonal wiring.
I made an instrument panel for my rally car (Escort Mexico 1) that measured battery voltage, charging condition, rpm and dwell angle (for checking the distributor points) and only needed a few wires to the battery and coil. You could also add a sensor for oil temperature.

Read up on CAN BUS and lights.
You may be able to replace the lamps with Can buss lamps

I like the idea of adding other things into the system. Oil pressure for instance.

Yay! The first MG A on the planet with CAN bus!

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only if there is room. if I remember from my Brothers MG, there was almost no room for an extra pair of sunglasses, the things were pretty small.