Archive for Lamp

I don’t lamp well

 

That was a long “next month”. A recap is in order. This post chronicles the long descent into complete and utter apathy.

 

In September 2014, I made some sketches for a lamp I wanted to build. The intent was to use the glass plate from a desktop scanner as the light diffuser, and laser etch a fractal pattern onto it to create a frosted effect, instead of being optically clear.

Here is a test piece I did, with a laser cutter and an image found off the internet.

 

 

The results were pretty fantastic. Fine details get lost, because it looks like the mode of operation is the laser heating up enough of the glass to chip off a small chunk before moving on. And so on, for the entire image. It creates great looking, even optical diffusion, though.

 

For another test, I decided to design and build a similar, but smaller lamp. Glass scanner beds are a limited supply. Using a glass tile I found at a craft store, I designed an arm to hold it onto a wall, a few centimetres away from a PCB containing some high power LEDs.

 

 

The initial model and 3D print is shown on my previous post.

Here is the final version, with some corrected measurements and better mounting point.

Lamp print

 

And the PCB arrived shortly after the last post.

 

Lamp PCB

Oops!

That’s mistake number one. Everything was intended to be clean and white, but I guess I forgot to change the soldermask from the default DirtyPCBs red. It’s not the end of the world. This is a prototype of a prototype, after all.

 

The first board was populated, and then the lamp languished for a year and a half.

 

 

Recently, I found it buried in a locker and tried plugging it in for the first time. With no prior consultation to documentation, I tried it on a bench power supply, starting at 5v. Nothing happened, so I turned it up to 10. At 15v, the semiconductor on the board released some smoke and glowed red for a few minutes.

Nope!

 

Back to the docs, I read that I had used an adjustable 5v boost converter, so that solved that.

I soldered up another board (I had two spares of the IC), including the DC barrel jack this time, and plugged it in again. Turns out I had the wrong polarity!

No smoke, but some troubleshooting proved that I had definitely fried the chip.

 

This was pretty much the limit of how much I cared, so I did what anyone would do:

I jumped over the active parts of the circuit with a power resistor, and ran the LEDs directly from a 19v laptop power supply.

 

 

Job done!

Next time I’ll build in some more safety factor.

Additionally, looking at the lamp from the side is really really bright because of the bare 1W LEDs. I kinda planned for this and put some slots in the side of the base for some acrylic sheets, but I’m quite done with this design.

This is a test

Quite a while ago, I did some experimenting with laser etching on glass. The intention was to backlight it and make a large lamp with some LEDs behind a large sheet of laser patterned and frosted glass.
Material costs pushed me towards scaling it way down and designing around a small glass tile that I picked up for a few cents. Just for an initial test, anyway.

The tile I chose is about 96mm², and just a hair under 7.3mm thick at the edges.

For the material acquisition side of things, I hunted for high power LEDs from Dealextreme, one of my favourite sites. They carried some 3W LEDs for a couple bucks, not bad. Then I checked Aliexpress. 1W LEDs were substantially cheaper, but I could only get them in quantities of 100. For $12. So I have some extras.

They measured out at around forward 3.2V. Current is about 120mA when the LEDs appear to be at max brightness. Theoretically they should go up to around 300mA, but this is good enough! I can’t see out of the centre of my vision!

I’m not really a huge fan of 3D printers, but I really wanted to crank this thing out quickly and using one freed up any design limitations for this janky part I needed.

After six quick iterations, I came up with this:

Printed Object

The angles turned out to be tricky to get right, but it worked out. Printed with support material on a Rostock MAX delta printer. The tile is held very securely with no fasteners, perfectly parallel to the base.

Balanced

It even stands up!

 

Bonus SolidWorks model view:

SW Lamp

For the actual circuit design, I went with all surface mount for easier custom boards, and some free sample chips from TI. See! That program totally works for them, I’m locked into this design now. Actually, it was the best part for the job that I could find. The LM3410, which is a constant current, analog dimming, PWM output boost converter. Yeah, pretty cool.

 

I found an Eagle library part that had the same footprint as the LM3410, and then I used my standard “print footprints at 1:1” method to find suitable library parts for my Chinese LEDs and salvage-bin inductor with no datasheets.

Parts list:

  • Inductor L1 – CDRH6D28-3R0NC – 3.0uH, 3.0A
    • The datasheet reference designs used anywhere from 4-20uH inductors. Less inductance just means a little more ripple current, which should be okay.
  • Schottkey Diode D1 – B260A-13, rated for 60V reverse voltage, 2A forward current.
  • Zener Diode D2 – I don’t have this yet! Reverse voltage drop between 21-24V. Might have to stack a bunch in series.
  • 1Ω R1, R3 – Two resistors, 1% tolerance, 1206, in parallel to make 0.5Ω
  • 100Ω R2 – 5%, 0805 for voltage overload.

Here are the results of my circuit building:

Lamp Schematic

The schematic is mostly a reference from the datasheet. Max current and voltage limits are a dependent on switching speed, the inductor I used, and the heatsinking of parts, so no hard-and-fast rules. I stretched it to the most high-power LEDs I thought I could get away with. That’s 6. Six LEDs. Worst case scenario, I have to jump one or two of them if everything starts to burn. Best case scenario, I’ve got ten of these boards coming, a dozen inductors, a hundred LEDs, but only three LM3410s.

For this build, I’m trying out the new Dirt Cheap Dirty Board service run by Dangerous Prototypes. I’ve used OSH Park and iTead Studios before, so this will be a fun experiment.

 

Originally, I was going to etch my own board using a laser cutter and the spraypaint etch resist method. Unfortunately, I have (temporarily, I hope) lost access to the laser cutter. For $14, this seems like a reasonable alternative.

 

I will update in a month or so, when the PCBs get here.