12v Relay bank to power off road leds

New to the forum but have been following arduino for a few years while i was researching an aquarium controller project. Now i Finally found a project I would like to attempt using arduino. In my head it seems pretty straight forward, arduino board, Sainsmart 8x 12v Relay board, display board.

This will sit in my Jeep and be used to switch on and off the various led lights. (Rock lights, fog lights, back up lights)
I will need a small display to show the various buttons or names of lights which will trigger them on.

With all the board options I am not sure if a mega 2560 is enough or overkill, I would like room for expansion.
My guess is at least a 4.5" inch screen but would consider as large as 9" and mount it in the dash replacing the head unit.

Thanks for your time.

Your question is impossible to answer without knowing exactly how many I/O lines you need. Nothing you have said suggests you need a Mega without knowing how many I/O you need.

raschemmel:
Your question is impossible to answer without knowing exactly how many I/O lines you need.
Nothing you have said suggests you need a Mega without knowing how many I/O you need.

Sorry I am not sure if I need a mega or not, was just planning for expansion and am looking for recommendations. As far as I/O, if you mean input output, the unit will reside in my Jeep so will only need a display to toggle the virtual switch, If you mean channel I/O, I would imagine 6 channels?

Sonicboom: New to the forum but have been following arduino for a few years...

Welcome. And great to hear you've started on your first project!

Looking at the 8 channel board, it doesn't use any clever interface to reduce the number of IO lines, so you'll consume 1 IO pin for each 12V relay you wish to control, but that's not the end of the pin count, because you mentioned...

Sonicboom: I will need a small display to show the various buttons or names of lights which will trigger them on.

Which means you'll need to count whatever interface requirements there are for the display you choose, and from the sounds of things you could be looking for a touch screen? Once you identify what it is you'll need for this user interface (including any switches for inputs if not a touch screen) you'll have a guide to whether you need a mega, or if (likely I believe) a more compact Uno, Micro, Nano etc might do the job just as easy and be easier to hide in your console.

All the best with your project, Geoff

So it comes down to the display I/O type. Graphics displays are sometimes SPI , which is 4 lines. (6+4) = 10 , so still no need for Mega. If the display is a "4-bit" type then you are looking at 4 data + 2 control + 2 backlight = 8 more I/O. If it's I2C then it's only 2 more lines and the aren't even digital I/O but A4 & A5 analog pins (I2C is " open collector " using analog pins with 4.7 k ohm pull up resistors) operating in digital mode. ( open drain if you want to be picky).

If mounting space and little extra money aren't a big concern, I'd go with the Mega... it doesn't hurt to have extra IO lines and memory. I have an automotive project that could have been done with an Uno, but I used a Mega and am glad I did, I've added a ton of extra sensors and outputs for things I would never have foreseen.

I have been using arduinos for 3 years and haven't run across any projects that can't be done with an UNO. Unless you really need a Mega, stick with the UNO. You haven't proved you need a Mega.

Thank you all for the detailed information, I read everyones post and decided to give an Uno a try, I received my Uno, 8 bank 12v relay board and a 2.8" TFT display. The display fits perfectly into the Uno and I was able to do a basic blink test to make sure everything worked. Uno board was fine and uploads were successful, only issue I see is a now might not have a way or am not sure how to connect the relay board with the display shield mounted.

Maybe a screw shield between the Uno and the display: http://www.crossroadsfencing.com/BobuinoRev17/ |500x434

Here's how to connect and make use of the opto isolation feature of your relay board... |500x163

Here is a schematic of a single channel .
OptoRelayChannelData-800.jpg

Sonicboom:
With all the board options I am not sure if a mega 2560 is enough or overkill,

Lol. Frankly I think any microcontroller is overkill for what a handful of rocker switches can accomplish.

Are you wanting these fog lights to flash in special patterns, or flash to music, or automatically sense the surrounding light levels to turn on or off themselves (that’d actually make a little more sense but still easily done analog).

If for the sake of finding a reason to learn the Arduino, that’s great. But when you’re talking about big LCD displays and replacing head units, you may wish to consider a Pi or something that will more easily and cheaperly give you things like an audio system, internet connectivity, bluetooth speakerphone functionality, and other junk.

3) This s/w works fine with just a standalone rotary encoder, but you will need ' to supply your own 10K pullups to 3V3. For a standalone encoder RA=CLK, RB=DT, & SW=SW '

This will sit in my Jeep and be used to switch on and off the various led lights. (Rock lights, fog lights, back up lights) I will need a small display to show the various buttons or names of lights which will trigger them on.

With all the board options I am not sure if a mega 2560 is enough or overkill, I would like room for expansion. My guess is at least a 4.5" inch screen but would consider as large as 9" and mount it in the dash replacing the head unit.

Of course we could have asked this question from the beginning but would you expect the arduino forum to ask you WHY you want to use an arduino ?