I am working on a project that is going to use an Arduino Uno and a 4-channel relay to control 4 different 12v accessories (lights). I would assume that using a 12v relay would be the easiest way to do it, but it would require external power that I don't want backtracking into the PWM pins of the Uno (also assuming that would be damaging). Keep in mind I assume wrong a lot. Is that an issue?
As far as 5v relays go, I have a similar project (already completed) that uses the PWM pins and external power to switch on and off a 12v LED strip. See attached for my currently working schematic. It is my understanding that if I were to use a 5v relay instead of a 12v, I would have to build a similar circuit.
Space in this project will be severely limited, so I'd prefer the first option if the second requires building that kind of circuit 4 times (for all the devices).
If I understand what you are doing I would just use a 5 volt relay to control the relays so you could just power them using the arduino power. If the relays need to be big and and the digital pins are not able to switch them you will have to use a transister to step up the power then swit h on the relays. You are correct in assuming that 12 volts into any there except Vin on an arduino is bad. What current do your light require?
I'm running two sets of 2x 12" CCFLs (the kind that you put in a computer, not the super-bright automotive ones) and a couple meters of 3528 LEDs. In a quick googling, it looks like both CCFL inverters draw something like 5mA each. I'm not sure about the LEDs, but being LEDs, they won't draw much either. There is no fourth channel at the moment, but I'm leaving that option open.
So then I would need to build a circuit like the one pictured above four times to control everything with a 5v relay. Am I understanding that correctly? If that's the case, then I could just skip the relay altogether. Which, now that I'm thinking about it, why can't I just do that in the first place?
since you have 12 and 5v already, you have that part done.
pick the voltage you like or have more of. it realy does not have any influence on the Arduino, or the relays or the relays circuit.
if you get a relay board, chances are it will have an on-board opto-isolator and all you need to do is power that.
the relay would have connectors for the load and there is no possible way to have the load back-feed the Arduino.
you say pwm as if you are planning on using pwm on the relay ? not possible.
if you want dimming, just keep your existing circuit and use the MOSFET.
