Hi, I'm a complete beginner at Arduino and I have a project in mind. I thought I would look to see if it's doable and get some tips on where to start. By way of background, I am a bit technical (was a programmer 40 years ago) and do some digital (as well as analogue) projects.
Most recently I have been doing digital audio projects with the Pi, D2A convertors and the like. Nothing with Arduino.
Being also a petrolhead, my idea for a project is to design a simple device to save my engine when it has a catastrophic oil pressure failure.
The very simple version is to measure rpm and activate a 12v relay when the revs get above a certain point (say 2k rpm). I can then use the 12v from the oil pressure sensor that activates a warning light to then cut the ignition with the relay.
Sorry for the lack of detail.
Key questions:
1 Can arduino work ok in a 12v car setting?
2 Can arduino count rpm continuously (well with reasonable frequency say 10 times per second)?
2 Can arduino activate a 12v relay?
Yes you need a DC-DC-step-down-converter to reduce the voltage to 5V
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Yes. You will need some kind of interface to change the signal from whatever it is to TTL 5V
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Yes. Again you need a small interface. Or taking a relay-module.
You should specifiy the current that you want to switch on/off with this relay
Currents above 5A require careful selecting a relay that can handle this big amount of current.
As this is a protection circuitry I would build it redundant. Two microcontrollers doing the same measurings so at least one works to indicate oilpressure OK / too low
It all sounds relative easy to do and the Arduino will 'work'! Before you go to far and invest is stuff you do not need or is not adequate read a great applications note by ST: AN2689 This will give you an idea of what you are in for. I was involved direct for many years and have seen many of the mistook made by others. From my background we expected a million of them to work first time every time for many years. That is total different then cobbling together a kludge. The application note will give you many of the problems and yes you may not see many of them in your application so you will get to guess which ones you need to protect for.
Then there is the American Automotive Council that has put together a bunch of specifications that will work for most but not all automotive applications, they fall under the AEC-Q100(101, 102, 103, etc). They will make good reading.
Thanks all, that's very helpful. I'll do some more research before embarking on any activity (and purchasing). The relay will only be switching around 0.5A at 12V - so 6 watts.
I'll need to work out a module to convert from the signal to the coil (something like a 12v square wave) to TTL 5V.
You also need to know how frequently the relay will be operated and for what length of time.
Is it also too late for your engine when the oil pressure drops? Will the lubrication still work during that time?
Yes there is a lot to think about with start stop conditions. Essentially, once the conditions fire the "alert" it needs to stay fired. To start the car the OP will be zero but at less than the low rev threshold. But once the OP falls below 15 psi at 5000 rpm (say) it needs to cut the ignition and stay cut until the ignition is cycled off and back on again.
If it can react faster than the driver in the heat of battle as it were, then it'll likely save the engine from catastrophic failure (seizing and bits coming out through the block). If that happens within 1/10th of a second it may save all damage.
Mind you, reading the note about transients in car electrics, it's quite off-putting!
Powering the Arduino from a self contained battery is very appealing. Connecting to the coil to measure rpm is not!