I'm a bit of a greenhorn when it comes to electronics, so I hope you'll bear with me here.
I am trying to create a small (test) project where I want one of three LED strips to light up at a time.
The LED strips are 12V, 4.8W, non-RGB - so only two wires going in.
I have yet to buy any PSU for either the arduino (mega 2560) or the LED strips.
Now, as far as I can understand, I will need to have an independent circuit to drive the LED strips, as the arduino cannot deliver that much current from an output.
As far as I can learn online, I will need three relays, and will wire them like this:
(With the relays being controlled by outputs on the arduino)
My questions are:
Am I right in understanding that I will need a relay?
Since I only ever want one of the LED strips to be on at a time, is there a smarter way of doing it?
Once my project is finished and not on the USB power, should I just get two identical 12Vdc, 1A, (5.5x2.1mm) power adapters - one for the arduino, and one for the LEDs?
LED'S are fine to share a power supply with the arduino as long as the power supply can meet the demand. If only one strip is ever on at a given time; you might be able to get away with only one 12v 1 amp supply, though a 2 amp supply would cover any mistakes in case more than one strip gets turned on. Switching leds with a MOSFET is usually a better option than a relay.
And if you want a really quiet switching, without putting mosfets into the mix, look into solid state relays.
They can be "slower" than mosfets but most people don't notice the 20ms or so lag time.
Ok, so it seems I'm not way off. As mentioned I am a novice in the world of electronics, but I will definitely read up on MOSFETs as I currently have no idea how they work.
As my project is supposed to seem old and quirky, I actually have no problem with delays or noise, quite the contrary.
Thanks for the help, I will just get a single power supply then.
One added question then:
If I draw power from Vin, can I both connect the USB and the power supply? So that I won't have to remove the USB in order to test the project?
Bittsen:
And if you want a really quiet switching, without putting mosfets into the mix, look into solid state relays.
They can be "slower" than mosfets but most people don't notice the 20ms or so lag time.
Well, actually, no!
"Solid State Relays" are mostly devices used for switching mains voltages, generally AC. The 20ms "lag" would correspond to switching the AC waveform on a zero crossing.
Relays indeed would be somewhat noisy for this application and more significantly, use more power than necessary. The problem with using MOSFETs is that logic level ones are necessary, even for as little as 500 mA here.
In fact, just transistors will do fine, pick them rated for 1A or so, NPN transistors can switch the negative side of the LED strips with the positive going to the 12V (presumably regulated - switchmode) power supply which can also power the Arduino at Vin though it might be wise to use a few silicon diodes to drop the voltage going in. You need current limiting resistors - 330 ohms would be fine - in series with the bases of the transistors. And of course, the same ground for the transistors and the 12V supply, as the Arduino
And yes, you absolutely can use Vin and USB simultaneously - the Arduino would be pretty useless if you could not - it has been carefully designed for this eventuality.
KenF: Those are very awesome - so awesome that I would have to move them to be visible from the outside of my enclosure.
I will try to draw up a plan both with MOSFETs and transistors as I want to be better at this. I think transistors will be a good choice (based on my limited knowledge), as I can always add the delay in software.
Just to give some context since you've asked. I'm building a MAME arcade machine, and for reasons I can't entirely explain, I want to craft an elaborate power-on system for the PC that powers it.
Step 1: Three safety-capped toggle buttons will gradually increase the voltage to a 5V panel voltmeter.
Step 2: A large knife-switch with two switches with keys (car ignition switch)
Step 3: A 3x4 keypad requires entry code
Each step is recessed into the side of the arcade cabinet.
When the PC is off, Step 1 is illuminated by a LED strip.
Once Step 1 is completed, the Step 2 LED strip turns on.
After Step 2, step 3 is illuminated.
Once Step 3 is completed, a illuminated pushbutton lights up, which is wired to turn on the PC.
When the PC is on, all LED strips are off.
It is completely stupid, but I choose this project to learn more about electronics, and because it seemed like a fun project while I wait for my arcade joysticks and buttons to arrive from Japan.
TL;DR: I have no strong need for the LEDs to turn on instantly.
