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USB Powered LEDs
KiTA
Registered User regular
Registered User regular
So, I have a project I want to work on:
http://www.mefeedia.com/entry/led-lights-for-a-usb-desktop-greenhouse/6002935/
http://forums.linear1.org/index.php/topic,891.0.html
Basically, I'd like to get a grow-light at my desk at work, as no windows severely cuts down on the plants I can have at my desk. Essentially, all I can have right now is a Spider Plant and maybe a Pothos.
My ultimate goal is a Venus Flytrap or a Cape Sundew, which require quite a bit of light. Plugging things into power is right out, unfortunately, due to fire codes, otherwise I'd buy a nice Desk Lamp and put in a 50W Grow Light, like I have in my closet.
So, About how many LEDs can I run off of one USB cable? I know the standard power output of a USB cable is 5v, but other than that, I'm lost.
My ultimate plan is for a hanging bank of LEDs, a blue (450) and red (675) mixture, in order to maximize the output -- I base that on the chart here:
http://www.fuzzlight.com/ledgrowlights.html
Maybe purchasing said LEDs from:
http://www.superbrightleds.com/leds.htm
In a mixture of these two:
Red
Blue
Or would a single range of purples work better? This looks like it hits the magic photosynth numbers, especially if I mix in 1 or 2 red ones to bump up the red waves a touch...
So, any Electrical Engineers around that could tell me if I'm being an idiot or not?
Edit: BTW, there's already 1 prebuilt kit:
http://usb.brando.com.hk/prod_detail.php?prod_id=00350
But I'd rather make my own, if possible... Especially if I could make the light bigger or brighter in the meantime, ya know?
http://www.mefeedia.com/entry/led-lights-for-a-usb-desktop-greenhouse/6002935/
http://forums.linear1.org/index.php/topic,891.0.html
Basically, I'd like to get a grow-light at my desk at work, as no windows severely cuts down on the plants I can have at my desk. Essentially, all I can have right now is a Spider Plant and maybe a Pothos.
My ultimate goal is a Venus Flytrap or a Cape Sundew, which require quite a bit of light. Plugging things into power is right out, unfortunately, due to fire codes, otherwise I'd buy a nice Desk Lamp and put in a 50W Grow Light, like I have in my closet.
So, About how many LEDs can I run off of one USB cable? I know the standard power output of a USB cable is 5v, but other than that, I'm lost.
My ultimate plan is for a hanging bank of LEDs, a blue (450) and red (675) mixture, in order to maximize the output -- I base that on the chart here:
http://www.fuzzlight.com/ledgrowlights.html
Maybe purchasing said LEDs from:
http://www.superbrightleds.com/leds.htm
In a mixture of these two:
Red
Blue
Or would a single range of purples work better? This looks like it hits the magic photosynth numbers, especially if I mix in 1 or 2 red ones to bump up the red waves a touch...
So, any Electrical Engineers around that could tell me if I'm being an idiot or not?
Edit: BTW, there's already 1 prebuilt kit:
http://usb.brando.com.hk/prod_detail.php?prod_id=00350
But I'd rather make my own, if possible... Especially if I could make the light bigger or brighter in the meantime, ya know?
KiTA on
0
Posts
So let's suppose you can draw 500mA.
Looking at the specs for the blue LED you linked to, it is rated for 20mA at 3.5V. This means that if you wanted to, you could potentially run a maximum of 25 blue LEDs from one USB port (25 x 20mA = 500mA <- current limit).
Looking at the specs for the red LED you linked to, it is rated for 50mA of continuous forward current at 2.1V. For the simplest case, you can run 10 red LEDs from one USB port (10 x 50mA = 500mA <- current limit).
You can also get sneaky, and put two red LEDs in series so that you have 50mA of continuous forward current at 4.2V (2 x 2.1V). In this case, you can run 20 red LEDs. The blue LEDs cannot be put in series because their forward voltage drop is 3.5V, and putting two of them in series requires 7V, which is greater than the 5V the USB port supplies.
For your case, you can mix and match the red and blue LEDs - just add up the required currents.
You will need a few resistors to control the amount of current going into the LEDs, though.
Edit:
You might want to do a bit of research on how to wire LEDs, and find some equations on how to calculate resistances. But what you want to do is possible.
Maybe I should look at some lower power or smaller LEDs, I don't know if 5mm LEDs or "Super Bright" LEDs are overkill or not... Are the power reqs for these LEDs about average?
The movie has a single miniature rose bush under what appears to be 3 standard light blue LEDs, perhaps I should buy some of these and look into running some tests, to see how many a single plant needs to survive off of... If I only need 3 per plant, especially if I use something reflective behind the LEDs to focus the light, then 25 would be absolutely perfect for my needs.
I think my ultimate goal would be a simple timer and 9V battery backup, in case the machine gets turned off at work or somesuch. But as just a basic proof of concept I think I'd be better off leaving that stuff alone for the time being.
Yup, sounds about right.
Well, for comparison, I run normal LEDs with 10mA and 1.4V forward drop and they're plenty bright. The LEDs you linked are rated at over twice the current (20mA/50mA) and at higher voltage. So the bright ones you linked to are higher than average.
I have no idea about plants though, and don't know if you actually need the bright LEDs or not.
It'll probably work - incandescent light bulbs are known to be ridiculously inefficient (around at 10% efficiency). Having said that though, I'm not really knowledgeable about plants... I just sorta water them, and they keep green and happy.
Good luck with your plan though!
Why not just run it from 9V batteries to begin with instead of bothering with hooking it up to the computer (and potentially frying your USB port/controller if you're not careful with your calculations and wiring)?
Unless you know exactly what you're doing you shouldn't screw around with the company computer like that. I don't know where you work, but willful destruction of company property probably isn't going to win you any awards.
I'm also curious as to how putting a lamp on your desk would violate fire codes.
Well, would a 9V battery survive for very long, running 9-16 LEDs? I'd probably be testing it first on a USB Hub connected to my home PC, of course...
And as for the Fire Codes, who knows? I wager it's the idea of 600 desks all having lamps and other shit plugged in at the same time. It's probably bullshit, a lot of their policies are, like "No Flash Games at Work, because a Flash Game once took down the entire (MyJob) Corporate Network". Absolute Horse Shit, but, hey, whatever.
For example, this was the first datasheet I found for a reputable brand - Energizer 9V. If you look on the right hand side of the first page, it's got a chart showing the milliamp hour capacity against current draw.
If you were drawing 100mA with your LEDs, then the battery capacity would be about 450mAhr, so you'd expect the 9V to last about 4.5 hours (450mAHr/100mA=4.5Hrs).
Seems unlikely, but possible. It'd take old, crappy, or WEIRD (as in power strip hooked up to power strip, etc) wiring to do, I think...
Um, yeah, I'm pretty sure our entire callcenter is wired based on the "power strip to power strip" method. But I donno.
They also claim ownership of anything you bring in. For example, an ergonomic keyboard or somesuch. Of course, that'd never hold up, but YOU try telling a multinational corporation about property rights as they're having security escort you out the door...