So I want to start a car- Explain to me like i'm five


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    @MarkGabb, hokay, ave a look at that one. it's rough, the values aren't right, but it's the basics of what I've done for the starter side of things. it shows the way switching the relays works, and that should help. Check the 'schematic' version - the fritzing version is intolerably messy and horrendous.

    I've just made a couple of changes to that schematic to show SDA/SCL and the relay connections and battery.

    So basically what we have there is a power regulator circuit with filter caps, the arduino, two relays indirectly driven and the explanation of what each one will do (start and on are self explanatory I'm hoping).

    You'd provide power to one side of each relays output contacts and the other side intercepts the appropriate ignition wire/s.



  • @lokki ok now im possibly even more confused but I think I follow it

    basicly I just need to find out the correct sizes of the parts needed then follow from a to b

    is there a program I can use to work out what sizes I should on the components? or a calculator of some sort...

    the more I look at it the more I can follow it....

    if I can ask what exactly are the transistors doing?

    I think that's all I have to ask for now

    your a scholar and a gentleman


  • Community Helper

    @MarkGabb, it can be a little confuzzling but break it down into sections.

    • You've got the power regulator which is just dropping voltage from the battery to appropriate voltage for the arduino and PN532 reader.
    • You have transistors driving relays x2
    • you have connections to the reader unit (5v/gnd/sda/scl)

    The NPN transistors will open a path to GND from the relay coil when voltage (HIGH) is applied out of the arduino. Think of it as a tap or valve. The resistor is like a safety mechanism that keeps voltage (LOW) until it's actually triggered. The diode bleeds off residual power from the relay coil once power is no longer applied by the arduino/transistor chain - it stops the relay self-triggering in kind of a flapping motion.
    So, appropriate voltage to one side of the relay, then an interrupted path to GND from the other side of the relay, with that triggered by the arduino via a transistor.

    Easy-peasy. ;-)


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    Wikipedia has a good entry on flyback circuits and why here.
    And another entry on pull-up/pull-down resistors here.

    It's good to know the why and wherefor of it all. And those explain better than I can, a teacher I am not.



  • @lokki ok that makes a lot more sense....

    so do I just take the +5v and gnd from the ardino on its same points?


  • Community Helper

    Sorry, I don't follow that - GND points will be linked together in/on the board there - so link regulator/battery GND to everything else GND. Anything that needs 5v gets that from the 5v side of the regulator circuit there, so all linked together again



  • @lokki all good you answered my exact question if I did garble it upon trying to get it from my head to my fingers.....

    ok so now I just need to find the correct sizes of components and go shopping :D YAY


  • Community Helper

    Awesome! Will be interesting to see what you come up with there mate!

    Yeah actually, it'd be easier to keep track of if you start a project thread, leave a reply here pointing to there.

    calculator for pull down resistors

    NPN transistors (I just used random ones from my parts bin)
    10uF electrolytic capacitors for filtering
    Diodes I used are 1N4001



  • ok so work in process ......
    currently working off @lokki design he gave me at the following link Here
    following is the shopping list so far

    Shopping:
    breadboard type stuff to put board on
    1 x arduino Nano
    1 x elechouse PN532 v3 Reader (cant substitute from all ive read...not worth the trouble)
    2 x flyback diodes
    2 x resistor (???)
    2 x bipolar transistors (???)
    2 x capacitor (???)

    computer IDE power leads will be sufficient for connecting external devices such as cabled to colum and cables to reader. probably main power in as well...clean and secure connection

    @lokki would you like this thrown in a new thread to keep it clean and so others can follow if they desire to learn later?


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    I had to edit a previous post, apparently I've used too many links and am getting flagged as spam in new posts... sigh.