Newbie Question - inputs and outputs (12VDC)

Hi forum,

very newbie questions for arduino, seeking for general setup and hardware for a project I need to work on.

This is for a car and as such most input and output will be 12VDC (11.4 vDC - 14.6 vDC) - still working through the final needs for inputs and outputs, however this is what i can share to-date)

I look to take a number of input from the vehicle which would loo something along these lines:

INPUT - 12VDC (ground - pulse)
INPUT - 12VDC (ground - const)
INPUT - 12VDC (positive pulse)
INPUT - 12VDC (positive Const)
INPUT - 5VDC ( pulse - speed pulse)

OUTPUT - 12VDC (to ground const)
OUTPUT - 12VDC (to ground Pulse)
OUTPUT - 12VDC (12VDC positive const)
OUTPUT - 12VDC (12VDC positive const) 1

for outputs although they will not pull 15A, not even close, I need build based n this possibility as the circuit protection is 15A in the vehicle)

Few questions around the above:

INPUTS - can these connect to direct to arduino board? (if no then best way?)
OUTPUTS - given the potential load I assume these would need a Relay board ( would have a 2 common. 12VDC and Ground) what would be best off the shelf to do this

any other guidance would be appreciated.....

In broad terms you will need some sort of interface between the 12vdc inputs and your Arduino, simplest may be 12vdc electromagnetic relays but check operating voltage range, Solid State Relays (SSR's) are an option or it may be possible to use optocouplers. Whichever you use you will need to make sure they are isolated as 12VDC is very bad for Arduino.

For outputs you will need a similar range of interfaces, as your Arduino can not directly switch 12VDC and can not switch a lot of current.

There are a huge number of "hits" on the Arduino search (I found "about 1,047 results" to the search 12vdc input to Arduino) I suggest you practice your searching and have a look at what others have done.

To drop the 12V signals to 5V resistor voltage dividers are a simple solution.

The method for switching 12V outputs depend on what you are driving. N channel logic level MOSFETs can be used for low side switching. P channel MOSFETs for high side switches.

great thx, i will take a look, was not sure what to begin searching for

To drop the 12V to 5V resistor voltage dividers are a simple solution.

you mean for inputs?

you mean for inputs?


If you can be more specific as to the nature of the signals that you want to input, we can be more specific with advice on how to condition and work with those signals.

Same for outputs.

working on that - looking at based needs - ill. loop back

Also, it would help to know what Arduino board that you are using.

It takes 10+V to open a regular FET gate so why not connect 12V--->resistor---->FET gate and when it's open, 5V from an INPUT_PULLUP pin can flow through to ground. It's almost opposite to why I bought FETs but those are logic level at least.

If the car system is running 14V, no difference and the Arduino is not getting 14V and/or spikes.

I'd use logic-level FETs to switch car power to run devices.

You can use an adjustable buck converter to take car V down to 5.3V and then use a 5.1V Zener diode to bleed off voltage over 5.1V, I think that should trim out ripple from the converter. Zener diodes are pretty cool and as I've been shown, they explode like firecrackers if enough reverse-voltage is applied! (aka what a EE with a reel of Zeners might do for fun when there's no boards to smoke)

Resistive dividers are NOT safe for automotive inputs due to the Voltage swings and peaks. Optocouplers are an inexpensive and reliable coupler, provided that the LED resistance is chosen to suit.

Outputs >5V can be MosFets or transistor driven relays, depending on what needs to be driven. If driving at =<5V then optocouplers will again do the job for logic.