Very nice to see the small approaches work.
http://www.greenpinelane.com/ has the big ones, DIY style, too.

@Michael: Yes, before RTFA-ing I thought those were capacitors and this was another of those art projects

If you look at the spot created by a bluray laser it will seem blurry and not well defined because it triggers fluorescence of the vitreous humour inside the eye. Does anyone know of any ill effects this might have ? (similar to UV ?)

had == HackaDay…

Looking back at the past few days posts, most are interesting and involve some brains, are unique and actually work. Debian on a router, the wirewrap cpu, avr rss reader, paintball gun for example are all cool projects. Even the proxxon drill press post is a good one b/c drilling pcb boards without breaking bits is a common problem for hackers. These are the reasons why I read HackaDay..

But stupid posts like this or the infiintely ridiculous one about the batteries wrapped in solar cells, are a waste and lower the credibility of this site.

Ever since Hack-A-Day went to Hacks-A-Day, there has been the consistent stupid post every few days. I wonder if they hired more staff, and couldn’t find someone with the most basic knowledge of electronics or physics.

@Paul AND 8Way
Paul was right “seeds” do not need light but “seedlings” do. As soon as the seedling breaks through the ground with its little green stem they need adequate light otherwise they will keep growing rapidly until they do and eventually become weak leggy (dead) plants. By looking at the post the three LEDs look like 1 watt so definitely more powerful than your standard Radio Shack variety and would have some effect as a light supplement but would be lacking as a primary light source.

Sorry to keep beating this up, but there are a number of issues with this design. :()

5V thru 50 ohms = .100 mA
/3 leds = 33mA/LED

Depending on the LED, that’s too hot and may prematurely burn them out.

Red leds drop approx 2.1V

.1/3*2.1=70mW each, or 210mW total. And that’s total power used by the LEDs. Assume a generous 50% efficiency for the LED, that’s about 100mW total radiated light.

That poor Atmel proc is not going to be happy. Atmels can only source 45mA IIRC. So he’s running that poor drive transistor way hotter than it is designed for. Current is limited to about 45mA due to the small size of the drive transistors. So make that 50mW total radiated light.

An external drive transistor (any old NPN switching transistor with a gate current limiting resistor will do) is necessary to source that much current. Or, alternatively, he could use multiple, (3 or more, IO pins to drive the leds.

He should be sinking the current thru the micro, not sourcing — it’s more efficient to sink current thru a FET than to source due to easier electron vs hole mobility.

A decoupling capacitor across the Vss/Vdd lines of the micro would help. Also a 10uF or so across the input power lines to reduce Vdd dropping when the leds turn on..

I stand corrected, and slightly better educated ;-).

@paul

Many types of seeds do need light to sprout.

Red/Blue is quite sufficient for many plants energy needs. However, plants also use quality of light to determine how to grow. The frequencies used for growth regulation are not necessarily red/blue.

hey now this sounds like some great innovative technology.