Fairly new to electronics so I’m sorry in advance if I come off as completely confused. I’m trying to build a small plant system, with watering and a few more functions. All of that is figured out but now I’m at “Feed the poor plants light” part and I’m trying to figure out how to do it in an efficient way. The base parts for this part of the project is:
2 * UV - LST1-01G01-UV03-00 Vf 3.4V 500mA
10 * Deep red - LST1-01G01-PRD1-00 Vf 2.05 500mA / 700mA
4 * Royal blue - XPGDRY-L1-0000-00601-SB01 Vf 2.82 350mA / 700 mA
2 * White - XPGDWT-01-0000-00LE1-SB01 Vf 2.81 350mA / 700 mA
And for power: 12V 8.5A power supply with a max rating of 110W.
What I’d like to be able to do from the Arduino is to dim the lights (per colour) and have them on for a certain amount of hours per day (it will vary with how much light they get from the sun and at what stage they are in). Also, I’d like to run all functionality through the Arduino, that’s the reason for not just using a simple wall socket timer.
After browsing through what feels like a thousand similar projects I’m still pretty confused, but I think I’ve found that LM3409 is the IC I want to use to rule it. Based on the AN-1954 demo board I’ve attached a simplified schematic of it which I think cover my needs but I really need some input.
First obvious question is, is LM3409 the droid I’m looking for?
Assuming it is I’ll need 4 of them and get out 6.8V, 20.5V, 11.28V and 5.62V. The AN-1954 datasheet has a table on page 11 for “Alternate Designs”, and there they have some examples of values and components to change but my electronics skills are too low to be able to wrap my head around it. The 4 alternatives all have several changes so I’m having trouble seeing what affects what. The questions I have now, and I’m guessing there’ll be more when/if someone replies are:
- How is the Vout decided? Is the step-down only by resistors? And does it only do step-down? (All examples and the base demo board all have higher Vin than Vout)
- In the first section it says “The circuit can accept an input voltage of 6V-42V.However, if the input voltage drops below the regulated LED string voltage, the converter goes into dropout and VO = V IN ideally.” That sounds like step-down only, but I’m assuming I can’t just give it 42V and it’ll automagically set Vout to something that doesn’t kill my LEDs.
- fsw, the switching frequency, is that something I really care about? Is that the speed of on/off or the max PWM frequency? As it’ll be steady light for 12-18 hours am I not really concerned by the micro seconds lag I’ll get when turning on/off and as long as the light doesn’t flicker during PWM isn’t that really something I care about either.
- I don’t really understand the IADJ pin and how it’s controlled. Should I connect that to an analogue port on the Arduino and control there or do I hook it up like the example and have 350mA/500mA/700mA depending on which colour / current I want to run them on? If I do send an analogue signal to it, how do I know what amount of voltage sets what constant current?
- EN - I’ll use that for PWM (if/when I want to dim), on of few things that seems straight forward. Or am I delusional?
- COFF, looks like I can ignore that? I’ll just not send any signal to EN when I want the LED off and that’s it?
- I understand this is much to ask for, and completely see if this one is ignored: If someone could take one of my four LED groups and explain which components to change, to what and why it’d be great.
Thanks for reading the whole way through, hope my questions makes sense, I didn’t miss too many details and that I’m not completely lost.