fub, posts by tag: led - LiveJournal

Three years ago, I did some calculations on swapping out the 50W halogen spots in the extension for LED equivalents. We did buy a few types to try them out, but none of them were to our liking: either the light was too cold, or it had a sickly greenish hue which gave people a ghoulish complexion. So while we had three various lamps hanging around, we didn't switch over completely.

But a few months back, we went to Het Groene Hert, an ecology store in the city centre that had recently been opened. There we saw a whole display of LED spots and we thought we could try one out and see what it was like -- the ad copy on the box said something about a 'natural colour'. And by coincidence, the person who runs the company that supplies these spots came by and we had a little chat about it. It ended with us taking one of the spots with us (with 3 2W Cree LEDs) to see how we'd like it.
We've had that one plugged in for a few months now, and we liked it. And since the halogen spots were failing one by one, I ordered 13 additional spots. Yes, it's a rather large investment, but it's worth it.
Yesterday the owner came by to drop the spots off. He also pointed out that he had replacements for the 12V halogen spots we have over the dining table -- so we got an additional five spots of those too. Today I did a complete replacement -- all halogen spots in the living have been replaced by LEDs.

The light is just a tad more 'bluish' and it seems like they're a tad less bright than the halogens -- but these are the best LED spots I've ever seen. Certainly good enough to get rid of the halogens and save EUR 20 per month in electricity!

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You can see some color difference (I didn't do any sort of colour correction on these photos, of course) but it's certainly within tolerances! I'm very pleased with the result, and especially with the savings.

I saw an interesting video passing by on my Twitter stream: visualising wifi signal strength with blinking LEDs and loooong exposures. It reminded me of klik's work on Leinligt.

See the video here.

So, two halogen lamps of the type we use in the extension cost EUR 7.00 -- EUR 3.50 per piece. They have roughly 1000 hours of operation (it says on the package that they will last a year, if you burn them three hours per day). That comes to EUR 3.50 per lamp per year.
A single warm white LED lamp (with 38 LEDs, so that should give enough light) costs EUR 21. But LEDs have a longer life. If you go by EUR 3.50 of deprecation per year, the lamp will be fully deprecated in 6 years. After that, you're 'earning' money.

So, simply looking at the cost of the lamps, the Return on Investment is at six years.

But wait! The halogens draw 50W, while the LEDs draw 2.1W! Let's do some calculations with that...
We have fourteen spots in the extension. Suppose we do run the lights for three hours every night for a year. And suppose we pay EUR 0.20 per kW/h.

Then:
14 * 50 W = 700 W. 700 W / 1000 = 0.7 kW. 0.7kW * 3h =2.1 kW/h. 2.1 * 20 = EUR 0.42 per night. For a year, that makes 0.42 * 365 = EUR 153.30.
So, using the halogens costs us EUR 153.30 per year (if all of the assumptions are correct, of course. But these being assumptions, we assume them to be correct anyway. ;) ).

For the LEDs:
14 * 2.1 W = 29.4 W. 29.4W / 1000 = 0.0294 kW. 0.0294 kW * 3h = 0.0882 kW/h. 0.0882 * 20 = EUR 0.01764 per night. For a year, that makes 0.01764 * 365 = EUR 6.44.

The difference between using LEDs and halogens is thus a whopping EUR 146.86 in electricity costs! That makes a cost reduction of EUR 10.49 per spot, which means that the break-even point, seen from the cost of electricity alone, is almost exactly after two years.
The third year, we'd be seeing a cost reduction of EUR 146.86 + (EUR 3.50 * 14) = EUR 195.86. And if we do an conservative estimation and assume that the LEDs will have an operational life of 10.000 burning hours, that means a total cost reduction of EUR 1566.88 during the life of the LED lamps.
Of course, that assumes the price of electricity stays constant -- which is doubtful to say the least.

I think I'll be ordering a few of those LED lamps to see if they can replace the halogen lamps... With a RoI of two years, that is certainly a worthy investment.

Also, feel free to point out any miscalculations I may have made!

Referring back to my previous post: if you turn off the internal pull-ups of the 12F675, charlieplexing works wonderfully.

I am pleased. Just switching one bit in the option register made it all work.

I wrote about the blinken LEDs for J earlier.

My approach was simple: use an 8-pin 12F675 PIC, and charlieplex four pins into 12 blinking LEDs. I built a small testing board and wrote the program to test the concept and schematic. It turns out that the pull-ups of the 12F675 are too weak to withstand the LED current -- which results in all LEDs glowing softly while one (the one that is supposed to be on) burns brightly. This renders the 12F675 useless for charlieplexing -- which is a real pity because the small footprint makes it very attractive to use that technique to maximise the number of LEDs that can be driven.
I should have realised this -- back in April I had some problems with the 12F675 precisely because the pull-ups are weaker than those in the 16F628A.

The same code worked pretty well in the 12F628A, though. I had almost reworked the board to accept my 18-pin workhorse of choice, when I realised that there was absolutely no need to charlieplex!
Sure, I could drive 12 LEDs with only 4 pins -- but why bother if I have fourteen pins at my disposal!? I had been so set on charlieplexing that I completely failed to re-adjust the schematic to the new parts I used.

So in the end, we built a schematic with fourteen direct-drive LEDs, with each LED connected to a pair of wires roughly the length of an A4 paper. I also added battery holders for three AA batteries and a switch (ghetto-style glued to the board with hot glue), and that was that.

As for the software, I used a linear feedback shift register as source for the pseudo-random patterns. For the timing, I used the one-second timer routine (based on the internal 4MHz oscillator -- not as precise as using a crystal, but this application is not time-critical), but I halved the number of clock cycles.
This results in a system that drives fourteen LEDs, blinking in another pseudo-random pattern every half second.

Tomorrow, J's work is being graded. I'm curious as to what she made of it, and her grade!

The inventor of white, blue and green LEDs, Professor Shuji Nakamura, was awarded the second Millenium Technology Prize.

The MTP is a bi-annual prize awarded to recognise "technological developments that have a positive impact on quality of life and sustainable development". The first one, in 2004, went to Tim Berners-Lee.

In his acceptance speech, Prof. Nakamura said: "This invention makes it possible to improve quality of life for many millions of people." It certainly improved my quality of life!

(Read the BBC article here)

Another type of LED clock: a LED hourglass. Pretty cool stuff, but alas no details on how they drive the LEDs.

I've finished building a scanning LED display -- these were ubiquitous in cheesy 80's TV series: the Cylons of old had these instead of eyes, and Kitt, the speaking car from the time when David Hasselhoff could still be considered 'cool', had it instead of a grill.

There are several schematics and kits out there to build this particular piece of nostalgia, but these all have something in common: the LEDs are either on or off, and that's it.
Of course, the LEDs used in the TV series had a serious afterglow, which some schematics reproduce by using elco's -- which has the disadvantage that the LEDs are slow to light up as well.
With a microcontroller, the solution is easy: use PWM! With a 16F628A that uses it's internal oscillator, I can drive 14 LEDs -- Kitt only had seven! You know we've made some pretty cool technological progress when you can have twice as much LEDs in your scanning display as you could twenty years ago. :)

It's finished now, and the effect is very, very cool. I've used the ultrabright, narrow-angle red LEDs -- I've tried capturing a little movie to show the effect, but they're too bright for my crappy webcam. You'll have to take my word for it.
Now I have to make one for klik, with blue LEDs -- like the one in my icon.

klik made me a LED christmas tree!