It’s officially Christmas at the house. The living room is all rearranged and the tree is up. Looks pretty good too. My family came up to visit so I had a lot of help putting it up which is always nice. It’s a bit of a chore to do by yourself but it’s fun as a group. I need to make it out to the trail of lights this year. Preferably when it gets cold.
Version 1.1 of the Luxeon LED test board was waiting for me when I returned from the frozen northlands. I spent some time soldering in the through-hole components this morning and then did the LEDs this evening. The LEDs were a little tricky but they all work and I didn’t burn myself which counts as success. I have some pictures of the finished product. The lights are bright. Very bright. The LM317 regulators get really hot. I have some heat sinks I’m going to have to attach but I was erroneously running the thing at +25V which may be part of the problem. The regulator dissipates power equal to (V_in – V_out) * I_load so if V_in is 25V, V_out is only 11V (3.4V forward voltage * 3 LEDs rounded up for other loss) and I_load is 320mA the power dissipated is 4.5W which is an awful lot. I’ll try again soon with the voltage set more sanely. Anyway, pictures.
Lights on
I think the next step is to get the Arduino in and useful so I have a little bit of time to wait.
I had some parts come in today. Six white LEDs to play with and some 2cm square prototyping boards. After the practice and note taking from last week setting up the simple current control circuit went quickly and I got the LEDs lit up. The new custom PCB should be in the mail and the Arduino duemilanove is back in stock at Sparkfun which means mine should be shipping soon if it hasn’t already. Exciting times.
LEDs in the breadboard
Heatsink mockup
The design work has progressed fairly well. I think I’ve figured out how to get all 20 of the lights to be independently controllable and the whole circuit should be fairly efficient. I may need to redo the design spec for the individual current controls though since the switching frequency is currently 10kHz but the new PWM controllers are higher frequency (~500Hz normally) which means I should bump the current switching frequency up to 40kHz or so. I’ll read through the datasheet again before going to the trouble to be sure.
Next steps are making up a real heat sink (probably with the remains of an aluminum can) with my little prototype boards attached and wiring up the play LEDs and populating the PCB when it arrives. It remains to be seen if I can solder the temperature-sensitive surface mount LEDs without ruining them but I have a few ideas. Everything else is through hole and basically doesn’t care about heat unless you just stab the glowing tip of the iron through the part.
On an unrelated note I get to visit Minneapolis for work. The forecast has been getting rosier every time I look at it. They’re predicting a balmy 20°F (up from 14°F) and 20% chance of snow for Thursday and 22°F on Friday which is practically shorts weather provided you are a bear or a wolf or some kind of other fur-covered non-human creature. It’s retarded cold for us people and I’m remembering The Cremation of Sam McGee by Robert Service.