Gas station without pumps

2014 October 19

Summer project 2

Filed under: Uncategorized — gasstationwithoutpumps @ 20:50
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In Summer Project, I introduced the project I’ve been working on all summer: a “kit” for making dimmable LED lamps, consisting of

  • a dimmer board that reads a potentiometer and converts it (non-linearly) to a pulse-width-modulated 9V output signal and
  • LED boards that hook up to the two wires of the PWM input signal, and that can be run in parallel,

and I showed the custom desk lamp I made for my son.  That was a fairly quick build, because it needed to be functional, but did not need to be very pretty—my son likes the exposed-wire look.  I asked him today how the lamp has been working out for the past week—he almost always uses it near the lowest setting, since he is either just filling in some shadows in an already lit room, or he is working at his desk while his roommate is sleeping.  In both cases he doesn’t need or want much light.  I suggested unmounting some of the LED boards, to get more control at the low light levels he needs.  Based on the measurements and calculations from the data sheets I did in LED board I-vs-V curve, he should be getting a range of  10–375 lumens from his desk lamp.  With only 3 LED boards, he would have a range of 6–225 lumens. But he likes having 5 shadows, so he turned down the suggestion. I considered changing the firmware for his lamp, to provide lower levels (has has all the equipment and software needed to reprogram it), but it is hard to get a duty cycle lower than 0.2% from the PWM controller.  If he really wants to go to low light levels, he could replace the 9V power supply with a 5V one, but then he’d have a range of 0.008–0.3 lumens, when what he probably wants is 1–40 lumens, which would need a 5.5V supply (not a standard size).  I think that he’ll sometimes need the 200–375 lumen range for task lighting when he is working with something fiddly late at night, so he is probably best off keeping with a full-power lamp.

The other project I mentioned was making a prototype table lamp for my sister, which needs to look a bit nicer, since she is considering making a series of table lamps using stiffened-silk shade.  I’ve now finished a prototype to send her, pictured below:

Here is the lamp, turned off.  The base is a wooden bowl from the thrift store, sanded so that it sits flat.  The upright is a standard brass lamp pipe, and the shade is just folded out of a 0.5m square of paper (the most common fold for making a paper cup).

Here is the lamp, turned off. The base is a wooden bowl from the thrift store, sanded so that it sits flat. The upright is a standard brass lamp pipe, and the shade is just folded out of a 0.5m square of paper (the most common fold for making a paper cup).

When turned on, the lamp produces a modest downward light and illuminates the shade.

When turned on, the lamp produces a modest downward light and illuminates the shade.

The lamp is done except for a knob for the potentiometer for controlling the dimmer. The only knobs I have are too large and industrial looking—I’ve ordered some smaller metal ones via Amazon, but they are being shipped from China, so I’ll probably have to mail my sister the lamp before the knobs get here. It turns out that if you want decorative, rather than ugly plastic, potentiometer knobs, the best source is companies that provide guitar parts.  The knobs for controls on electric guitars come in a wide variety of styles, some of them quite elegant.  (But guitar parts are also a fairly expensive way to get knobs, so make sure that you really like them!)

When I first assembled the lamp, there was a rather nasty flaw in the design, resulting in unintended shadows on the shade:

At first there was an extra shadow in the middle of the shade that I did not like.

At first there was an extra shadow in the middle of the shade that I did not like.

With the shade off, it is easy to see where the extra shadow come from—it is the knurled nut connecting the up-facing LED board to the power wires.

With the shade off, it is easy to see where the extra shadow come from—it is the knurled nut connecting the up-facing LED board to the power wires.

The fix was easy—I just put the screw in from the top of the board, so that there was no large assembly to cast shadows:

Here is a closeup of the top part of the lamp, showing the top LED board facing up with the knurled nut on the back of the board. The two end LED boards face down, again having the knurled nut on the back, along with the heat sink.  I had originally planned to support the shade with the same 10-gauge copper wires that power the boards, but I realized that the cooper would corrode in a humid atmosphere, which might stain the shade, so I made a support out of 1/8" 316L stainless steel welding rod, using a little hot-melt glue to attach pony beads to the ends, so that the rods wouldn't poke holes in the shade.

Here is a closeup of the top part of the lamp, showing the top LED board facing up with the knurled nut on the back of the board. The two end LED boards face down, again having the knurled nut on the back, along with the heat sink.
I had originally planned to support the shade with the same 10-gauge copper wires that power the boards, but I realized that the cooper would corrode in a humid atmosphere, which might stain the shade, so I made a support out of 1/8″ 316L stainless steel welding rod, using a little hot-melt glue to attach pony beads to the ends, so that the rods wouldn’t poke holes in the shade.

The shadows cast by the LEDs with the corrected orientation of the screws is much cleaner than before.

The shadows cast by the LEDs with the corrected orientation of the screws is much cleaner than before.

I still have to write artist-level instructions on how to put together the electronics for a lamp. That will probably require a few more closeups of the lamp (with better lighting), which I’ll take during the week, before shipping the prototype to my sister.

1 Comment »

  1. […] Summer Project and Summer Project 2, I introduced the project I’ve been working on all summer: a “kit” for making […]

    Pingback by Desk lamp | Gas station without pumps — 2014 December 28 @ 18:47 | Reply


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