DIY LED Drivers with Microcontroller

[Brian Ward]

You can get Arduino system pretty cheap on ebay.

 

They're surprisingly cheaper on eBay ($10 vs $30). Any particular seller that you've found reputable?

[Guest thefishman65]

I was going to use the one being developed on RC so I have not looked. I can point you at a thread of some one (with comments from others) that bought them from ebay.

 

Using other people boards is usually cheaper (they mass produce more than you), but it usually takes up more room. The only reason I did my board was for individual string control. The reason it has 8 was because of the board house I picked.

[Chad]

I just ordered from this guy http://myworld.ebay.com/b2cqshop/?_trksid=p4340.l2559, the stuff he sent me seems to work and the shipping was resonable ($10) and took ~7 days.

[Brian Ward]

Using other people boards is usually cheaper (they mass produce more than you), but it usually takes up more room. The only reason I did my board was for individual string control. The reason it has 8 was because of the board house I picked.

 

OK, I understand what boards you're talking about selling me now. Is there any major cost difference or functional advantage between buying these vs. using your printed boards? I'm leaning toward doing 6 CAT4101s with an Arduino for each fixture. That will maximize my flexibility for each fixture but I'm still playing with pricing.

[Guest thefishman65]

I am confused with your question.

OK, I understand what boards you're talking about selling me now [the ones I designed]. Is there any major cost difference or functional advantage between buying these [you have only mentioned my boards unless I missed something] vs. using your printed boards?

 

My boards can be under populated with 6 CATs. Also if you don't mind a soldered wire rather than a screw terminal 6 PWMs can be done.

[Brian Ward]

I am confused with your question.

 

My boards can be under populated with 6 CATs. Also if you don't mind a soldered wire rather than a screw terminal 6 PWMs can be done.

 

I didn't understand initially what boards you were talking about selling me. Now I see that you had some boards printed that just require components to be mounted to them. I'm assuming you have extras of these that you are willing to sell off?

 

I'm planning to do 4 Arduino controllers - 1 in each fixture - each of which will provide a PWM signal to each of 6 CATs. Instead of POTs, I just want to fix the current @ 1A and use the PWM signal to dial that up or down.

 

I'm fine with skipping the screw terminals and can use a wire harness instead. Not sure if that will be necessary or not.

 

Right now I'm trying to figure out if the 24V 156W power supply is sufficient for each of my fixtures. If I have to step up to the 300W, it could be more cost-efficient to go with the 12V 156W supply and use a couple extra CATs. I'm planning 2 12V fans on each heat sink that require about .5A each. That with the Arduino is getting me close to the current limit of the 24V supply.

 

One thing I'm somewhat concerned about is power use. If I'm maxing out the amount of current the power supply can source am I also using that much electricity? For example, let's say I wire 12 LEDs in parallel, each one off of a CAT to regulate the current. I need 12A to drive all 12 LEDs, but I should only be consuming 36W of power (or slightly more due to efficiency) if I assume 3W/LED. This configuration, however, would max out a 12V 156W power supply (capable of sourcing 12.5A). Is the CAT sinking the balance of the power (~120W)?

[Chad]

I just ordered from this guy http://myworld.ebay....sid=p4340.l2559, the stuff he sent me seems to work and the shipping was resonable ($10) and took ~7 days.

 

To add to my review of the seller...

 

I have put the arduino mega through some serious calculating by including math.h, running a bunch of calculations (my moving Gaussian sketch works great, by the way, I can't wait to see it in action full-scale!!) and tested most of the pins as both inputs and outputs... it works great. One thing to note, though, not sure if it matters, but if you look at the picture on the arduino website, there is a "made in Italy" label in the top right of all the boards... mine does not have that label.

 

The breadboard I got from the same guy, however... I cannot say the same thing about, half of it has very high resistance (~15k ohm) internal connections.... That was about 3 hours of my Saturday morning trying to figure out!

 

Brian, when calculating your costs, don't forget if you go over the need for 6 PWMs per standard arduino uno or comparable, you will need a separate chip like this to add more PWM outputs (more cost ~$6 +board to hold it, and more work writing code).

[Chad]

^actually scratch the extra chip... after some more searching I found this... It might be quite useful. PWM on any output accomplished with code. I will download the code and go through it when I have a chance.

 

http://www.arduino.cc/cgi-bin/yabb2/YaBB.pl?num=1268806013

[Guest thefishman65]

I think I have 4 extra boards, if no I can get some more made.

 

Pots are nice because then you have 255 steps for dimming. However you can save ($0.80 each IIRC) by soldering a wire (0 resistance). Also if you use the resistor I supply you will b imited to 900 ma - you can get your own resistors.

 

Not sure you could get a full amp, general practice would say .866 amps (80% usage). O f course if you turn then down to 20-21 volts you might be able to go higher befpre they heat up.

 

Yes, the CAT just eats the rest of the power. One reason a power supply that can be turned down is a good (highly suggested) idea.

[Chad]

Rob, it looks like Brian will need four, and I will need two, what is the minimum for a re-order on your board?

 

Brian, I have been thinking... could you synchronize your arduinos by using one RTC for all of the boards?

[Brian Ward]

Brian, I have been thinking... could you synchronize your arduinos by using one RTC for all of the boards?

 

That's something I'm planning to tinker with. My thought right now is to actually take the wire that connects the DC8s together for the AC3 and extend that through my fixtures, have the arduino read the outlet on/off signals that I send and change the lighting accordingly. I've got to find out if someone has already reverse-engineered the interface or if I have to do it.

[Brian Ward]

I think I have 4 extra boards, if no I can get some more made.

 

Yes, the CAT just eats the rest of the power. One reason a power supply that can be turned down is a good (highly suggested) idea.

 

Let us know what the minimum run is to get more boards.

 

That's good info on the CAT and sorta what I was afraid of. I'll have to work on my design to minimize power consumption.

[Guest thefishman65]

I order 10 boards at a time for $100. Then keep offering to folks . In the end I may get stuck with extra boards, but I was going to do it anyway.