Hey guys, finally thinking about upgrading the rats nest of a design currently in my truck to handle the accessory and air system. Currently I have a Freeduino with a relay shield and another PCB project board that handles a few connections to my truck's accessories.
I have the 20x4 (http://www.adafruit.com/products/198
) display connected via the i2c backpack (http://www.adafruit.com/products/292
). Working great and looking great, but too bright. Going to want to dim this down and hopefully control it with the dimmer switch in the truck (running thru a voltage divider and PWM the back-light off the result).
I want to create a custom board using an ATmega 168/328 that will replace the Freeduino. Using this guide (http://www.instructables.com/id/Perfboa ... /?ALLSTEPS
) to make a stand alone Arduino controller. I want to run 3 relays using the digital out pins, have 3 switch inputs, have 3 analog sensors (one for pressure, one for temp, one for voltage from dimmer switch on a voltage divider) and have the output going to the LCD.
So far, everything seems to be working fine, just a rats nest of wiring and I want to clean it up. Here are my questions:
1) If I use a ULN2803 for the outputs to drive low current relays, do I need to have a resistor in line between the digital pin and the input on the 2803? It looks like I don't, but I want to make sure. I know I needed one for the transistor setup I had first, but it seems like the Darlington Array doesn't need it.
2) Would I be better off separating the PWM LCD to a different (smaller) AT chip that is solely dedicated to that function? I think I will be fine using the 168/328 but I'd like to be sure.
3) Where would be a good source to get one board etched up that can pull an Eagle file and not cost an arm and a leg? Talking about possibly a 5"x5" board (though I'm pretty sure I can shrink that.
I know about the analogRead having issues with multiple sensors and how to counter them, that's already on my list of things to change with the code. Currently only running one sensor so it doesn't seem to be an issue.
Ideally for this project, I will:
Build the Arduino circuit and test
Connect the 3 digital out pins for the relays and one PWM pin for the LCD controller to the ULN2803 and test
Incorporate current sketch and test
Add PWM using the voltage divider from the dimmer switch and test (and tweak and tweak and tweak)
Then build the board in Eagle and find someone to make it real
Assemble and final test