Need to Test Some LEDs?

I’ve been buying some 3W LEDs from various sources for a project.  Each of those sellers makes wildly improbable claims about the brightness and chromaticity of their LEDs, but I didn’t have a good way to verify them and see which are best.  I found a light meter in the i3 Detroit eLab, but getting consistent readings from that was difficult.  The readings depend upon ambient lighting, angle to the LED’s axis, distance from the emitter, etc.  I finally came up with an idea for a (relatively quick) little jig to get consistent readings which at least allow me to compare LEDs to each other.  As a bonus, the materials are very cheap and it’s easy to build.

Complete LED tester

Complete LED tester

LED mounted on the base of the jig.

LED mounted on the base of the jig.

The LED is mounted under a piece of shim stock cut to form electrodes.  The electrodes can either contact the pads on the heatsink, or the leads on the LED itself.

This is the view from the end where the light meter probe fits into the laser-cut opening.  Because no problem worth solving cannot be solved with a laser cutter.

The interior of the chamber is painted with flat black paint to reduce the effects of any light leakage at the joints and reflections from the walls due to angle of view of the LED.

View of LED from the business end of the jig

View of LED from the business end of the jig

This jig is easy to connect to a current-limiting power supply, and it blocks out ambient light well (the meter reads 0 lux with the power off).  What it does not do well is provide removal of heat from the LED’s heatsink.  So it’s important to run the LED at a current level that does not generate a lot of heat, possibly wrecking the chip.  I used 600 mA for an LED rated at 700 mA and wavelength of 660 nm.  Blue LEDs generate more heat, so they would have to be tested at an even lower power level.  But the point here is to compare LEDs within the same lot or between lots, not to get calibrated readings that can be compared to standards.  That would require a much more expensive meter.

Why buy all these LEDs?  I’ll save that for a future post.

2014-11-22 14.23.31

i3Detroit: Now available at the speed of light!

Almost a month ago, a few i3 Detroit members decided that the wait was over: we had been talking about it for over two years and we couldn’t wait any longer.  We were ready to reach out and take our place boldly, sharing our thoughts with others through the filter of experience and across the bandwidth of our maker community.

All we needed was a few good people, and our plan started to resonate.

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Twitterbot, part 0

Many hackerspaces have some form of notification system, allowing members to publicly announce that the space is welcoming guests. These systems take many different forms, but many boil down to one of two types of systems. The first is one with all the bells on, watching the space with motion sensors and people-detectors and automatically alerting interested parties that people are in the space! The other is effectively a simple switch inside the space and some local status indications, plus some simple scripting running on a machine somewhere to post to Twitter, or to update a website, or whatever.

Way, way, way back in the day, when dinosaurs roamed the Earth and i3Detroit still occupied its first home in Royal Oak, MI, we had such a system.

The initial plans for the system were spurred by HacDC’s doorman switch, a PIR motion detector just inside the door which posted periodically when motion was detected in the space. This was useful for members to see if others were around, but not really aimed at getting guests to the space.

i3Detroit decided (in the sense that any do-ocracy decides things: someone proposed the idea, no one objected, and batch scripts ensued) that a voluntary switch with a single-frame image would service two needs: 1) respect privacy (webcams tell the world that $whatsherface is alone in the space…) and 2) offer the world an ever-changing indication that i3Detroit was alive and vibrant.

Affectionately and simply dubbed the Twitterbot (or, for some reason on the wiki, the Welcome Switch), this system consisted of a toggle switch and LED in a 1-gang box. When the switch would change from the “closed” position to the “open” position, the system would post that the space was open to guests to Twitter and our website.

Revision 0 used a D-Link network camera, with an opto-isolated input and a relay output. The switch wired into the input, and the LED was run from the relay output. Every 30 seconds, a batch script running on a machine elsewhere in the universe requested the switch status from the D-Link. If the state had changed to “open”, the script asked the camera to take a picture.

The resulting picture would then be posted to Twitpic, and a message indicating that the space was open for guests would be posted to Twitter and to the website.

If the switch went to the “closed” state, a message was posted to Twitter and the website indicating the space was no longer open to guests.

If either post succeeded, the script then changed the LED state to match the switch state.

This led to a neat cultural thing: Whenever someone (or someones) would open the space for guests, they would tend to pose and make ridiculous faces. Soon, a box of silly hats found its way to the area where the Twitterbot lived, to add further festivity.

Revision 1.4 moved into the space, running a Perl script on an ancient desktop machine running Debian, largely to avoid the whole “HTTP GET requests into the space every 30 seconds” thing.

Revision 1.7 saw Twitter move to OAuth-only login. However, Twitpic still allowed posting using basic authentication, so the system posted a “closed” picture as well.

The system then lost the camera, as its owner wanted it back. The switch and LED were then wired up to an RS-485-connected IO expander. The IO expander in turn was routed via an RS-485-to-RS-232 adapter and an RS-232-to-USB adapter to the Debian box.

Twitpic then went to OAuth too, and the Twitter announcement itself disappeared. Soon, the poor Twitterbot was reduced to simply updating a WordPress widget, and swung freely from its Cat5 cable, alone among the myriad hardware that festoons the wall near our front door.

Old, sad Twitterbot.

Unloved, and barely used, the Twitterbot languished in silence for months, until one day…

Next time, in part 1 of the Twitterbot saga, we see our fearless adventurers solving problems and designing things, for the good of all mankind!

Or, you know, a showing-off of the redesign of the Twitterbot.

PCB Mill Dust Collection System

Recently, we discovered that the dust collection vacuum unit for our LPKF Protomat C30/S was leaking powdered fibreglass dust all over the under-desk cabinet in which it lives. This of course being unacceptable from a safety perspective (powdered fibreglass is not a carcinogen, but is a major irritant in general) and from a cleanliness perspective, we took it upon ourselves to figure out what went wrong.

It turns out that the machine had been operated for an indeterminate amount of time without pre-filter bags, and the filter had failed under the load of nearly 3mm of caked-up fibreglass and copper dust. D’oh.

So, a quick Google search yielded exactly zero sources for filters (but LPKF will sell you the bags, $35/5).

In true hacker spirit, this did not phase us at all. After all, how hard can it be to build a dust collection system from scratch?

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Full Spectrum 40W Laser Cutter Up and Running!


At the Red Bull Creation this year, i3Detroit won a 40W Full Spectrum Generation 5 Hobby Laser with a 16″ x 12″ bed.

This prize was awarded to i3Detroit as the Team Choice award prize.

After much design work, purchasing, and duct installation, we now have the machine up and running in the Fab Lab. Wiki page for the machine.

We will be having training classes on the machine in the coming weeks, so watch this space and our mailing list for information.

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