Good morning,
I'd like some help with an academic project I'm working on. I'd like to control the possibility of starting or stopping my car via SMS, but I'm not sure which relay I should use to connect, for example, to the car's petrol pump.
My car is a 1992 Honda Civic, with a 12v, 45ah battery.
Diagram attached.
Thank you.
If you want to do this you should do this via the key ignition, but i think in general it is not such a good idea.
Hello, thank you for your reply. It's just an academic project, but the choice of hardware has to be justified. That's why I don't know if I can use just any relay or a specific one.
Your topic has been moved. Please do not post in "Uncategorized"; see the sticky topics in https://forum.arduino.cc/c/using-arduino/uncategorized/184.
Find out the current draw ftom the pump, and buy a relay module specified for that current. It preferably pulls the coil current from the 12 volt system.
I am still thinking the ignition is the place to switch something. Sure you can stop the pump, but the engine won't start after you switch it back on again.
Thank you for your replies. OK, I mentioned the petrol pump (~10A) as an example. It could be the ignition. I just don't know which relay to buy. Maybe one up to 30A might be safe to switch on in the ignition?
I guess you probably need 2 relays, one to switch the ignition, and one to switch the startermotor. If you connect them just near where you switch the car with the key normally, than 30A should be plenty. You will also need some circuitry to drive the relays, ideally a transistor each and and Opto-coupler driving that to fully isolate all of the rather unpleasant electrical noise from the microprocessor.
Hi, @juliorocha
What we need now is a copy of your circuit, a picture of a hand drawn circuit in jpg, png?
Hand drawn and photographed is perfectly acceptable.
Please include ALL hardware, power supplies, component names and pin labels.
Your image in your first post does not show any of this data.
I am not sure why you have moisture/water detectors in your project.
If you are going to remotely start the vehicle as well, you will need to detect;
1). Hand (emergency) brake status.
2). Gear selector status (Neutral).
3). Oil pressure (to check if and when the engine is running).
4). Battery status (to check that it is charged/charging).
5). Engine Temperature (to make sure the cooling system is not overheating).
So many system checks, I would leave remote starting OFF your list.
Tom.. 
Hello everyone and thanks for your help. The idea is not to start the engine, but to have the possibility of starting it normally with the key or remote control, on site.
The purpose of this project is a prototype that, in the first phase, detects whether there has been an accident. If an accident is detected, due to a collision, rollover or skid and enter a river, the latter without overturning and hitting an object, the engine is automatically turned off, opening the relay that is connected, for example, to the ignition.
If an accident is still detected, I can still know the speed I was traveling 5 seconds before the accident and the location of the car.
In a second phase, I can turn off the car (via SMS) if it is stolen from me. It is this relay that I need to know the characteristics of.
--
i use the online translator... 
sorry..
In the case of a petrol car, use a relay on the ignition that can be disabled via SMS. 30A will be more than enough. Still who is gonna steal a 1992 Honda civic. If someone is going to steal your car, they would anyway have to hot-wire it, so then bypassing your theft protection is not going to be much of an issue i suppose.
That's fine, saves us from having to do so. The whole project sounds a bit iffy to me still though.
That is all assuming that the device you intend to create has survived the crash and is still being powered.
Ok. thanks. its a honda delsol.
If the ignition isn't turned on then it doesn't matter if you turn the fuel on or not. The car will not start unless the ignition is on.
If you turn the ignition on then it will turn on everything else like the fuel. The ignition system is the ONLY place to try to accomplish this task.
This is some real world information. This can help you in your presentation. Arduinos were designed for and are are intended for experimentation and learning, often with breadboards and loose wires that eventually break if vibrated. Most important, the boards are not protected against harsh, dirty or electrically noisy environments found in industrial, automotive and other commercial applications. It is unreliable as it is not suitable for industrial, automotive and other commercial operation.
There is many good app notes such as AN2689 by ST on automotive electronics. reading it will help you a lot.
https://www.st.com/resource/en/application_note/cd00181783-protection-of-automotive-electronics-from-electrical-hazards-guidelines-for-design-and-component-selection-stmicroelectronics.pdf
Also take a look at these: Distilled Automotive Electronics Design | Analog Devices and
Transient Voltage Suppression in Automotive Applications
AEC-100 https://media.monolithicpower.com/mps_cms_document/w/e/Webinar_-_Fundamentals_of_AEC-
Understanding Automotive Electronics, An Engineering Perspective by William B. Ribbens
(PDF) .Understanding Automotive Electronics, Seventh Edition An Engineering Perspective by William Ribbens | Roman Perez - Academia.edu
