Howdy all;
I'm totally, completely, utterly starting from scratch in the Arduino/micro controller/electronics world and need to get a reality check. I've been writing software for many years, but have no hardware experience. I want to learn while building some specific projects, and want to make sure the Arduino is the right platform for the task. I appreciate any guidance you can provide.
My first project is to use the Arduino as an lighting controller for a number of LED lighting strips in my house. The strips all run at 12VDC, but draw a lot of amps (3 per strip, 10 strips in total). I've broken the strips into groups for different areas I'm lighting. I have 4 groups - three are single color, and the other is RGB and can be any color. Since I'll be controlling 30 amps total, I imagine that's not the kind power to put directly through the arduino. Ultimately, I want to control the brightness of the lighting and also the color of the RGB group. Ideally, I'd like to have the arduino be network accessible and be able to control it remotely from other parts of the house (or the world, i suppose =).
First off, do these seem like reasonable goals?
Here's my very basic knowledge & guesses of how it could work:
I would need a relay to turn on & shut off the mains power (110VAC) that supplies the power supply for each discrete group of lights. I would also need an LED compatible PWM fader control that could handle the necessary amperage for each group of lights (each 16ft strip pulls 3amps @12VDC, according to their specs, and the largest group would be 3 strips). This covers the basic on/off/brightness controls.
The other aspect would be color control of the RGB lighting. I can give you details or links to the light's product page if that would help. These strips are also 12VDC and are powered with 4 wires - presumably one ground and one wire for red, green, and blue. They came with a color control unit, but it has a limited set of colors pre-programmed. My theory is that a PWM fader controlling each color is what determines the final color. Any merit to this theory?
That's it for now. Any thoughts or guidance would be great. I'm ordering a starter kit from ladyada shortly to begin figuring this all out. Thanks a bunch.
Well you have made the right thing for choosing the arduino because it's perfect for what you have in mind.
Now if you want to power your LED strips with PWM functions you will need to use a MOSFET transistor that can handle a 3A load.
There is an add-on that can allow you to control your arduino via Ethernet(http://arduino.cc/en/Guide/ArduinoEthernetShield)
Now you are right about the RGB LEDs you can create colors by "mixing" PWM levels of colors.
You have 255 levels of brightens for each color so it gives you tones of colors to play with. So if you want to make yellow you give 255 to the Red, 255 to the Green and 0 to the blue.
You can find more info on the web about RGB and PWM.
hey systemx - thanks for the information. Let me see if I understand properly:
The arduino would send a low voltage/amperage input to the MOSFET, which acts as a gate for the high voltage/amperage trying to pass through the MOSFET out to the strip of LED lights. When the MOSFET gets the low voltage signal from the arduino, it closes the circuit and powers the LED strip. When the low voltage stops, the gate opens and breaks the circuit. And then the arduino can use its built-in PWM to determine how often the gate opens and closes in order to vary the brightness? So far that's what I'm thinking - please let me know if my ignorance is showing.
Where is a good resource to buy MOSFETs that would work well with the arduino and support up to 12 amps of throughput?
Thanks again for the quick response.
Well your on the right way but when the arduino gives a low output(0 volts) the gate opens and there is no light, and when the arduino gives a high output(5 volts) the gate closes.
Now PWM is the rate at which you close and open the gate, if the gate is open more time then it closed then you get a dim light.
I would say that you can buy MOSFETs from ebay for cheap, you just need to know what ratings you need.
Thanks for the follow-up systemx;
I'm going to ask folks for general recommendations on suppliers for MOSFETS (I don't think I'm smart enough about what I'm buying to trust myself via ebay)
