Past posts of this series:
I bought some stage lights from Playmobil (see also my post on the Playmobil parts):
They have a diameter of 1cm inside. So I thought „why not buy big LEDs that fit in there?“. I measured and looked through the online shop of http://www.conrad.de. I figured out that the 10mm LEDs will not fit because they have a slightly wider ring on the bottom. The 8mm LEDs also have this ring but this one is about 10mm so fit perfectly.
I bought 9 of these in the colors red, yellow and green (after the guy at the parts counter wanted to also sell me white ones. Right before going to the checkout I saw that they cost 4.95 EUR each. He nearly got me. Now I know I always have to ask for the price of all parts, even if they seem nearly the same…).
Back home I calculated the resistors needed and came up with the following results using http://ledcalc.com/:
What I didn’t think of was how bright they would be. When I connected everything I was a bit disappointed but having a look at the data sheets I understood why and blamed myself. They only have 3 mcd of light. That’s really next to nothing. A candle has about 1000 mcd. So I will go back to using 5mm LEDs that are cheaper and easier to find in various colors and with a much higher mcd value. Lesson learned!
I then just ordered a cheap LED set from ebay with higher mcd values and 5 colors each in sizes 5mm and 3mm. Those are quite acceptable in brightness. Only the green LED is very dark (although it has the highest mcd ratings… can anyone explain that? I experimented with resistors from 82 ohm to 100 ohm but it is not very bright). I won’t do the full resistor math here, just use an online LED calculator
The light distribution is very wide but I also had some LEDs from a cheap starter set which are more like a spot light. I will combine both and will place the spots. I also have red, blue and green LEDs from those but the green ones have the same brightness problem so I will just use red and blue. I combine the red and blue spots together with the yellow ones from the set in the Playmobil spots and have two white spots at fixed points at the side of the stage for the disco mirror ball (5cm diameter) I bought from Conrad:
The spotlights are mounted on a 4mm aluminum rod:
That is a tight fit but is just the right tension to not move easily and be able to move the spots.
Schematics LED controller board
From my HUEify project I had good experiences with using a MOSFET to drive LEDs so I bought some BUZ11 again (I know, not the best ones to use but at least here a very cheap way to go). So the plan is to drive the LEDs in color groups, each driven by a BUZ11. In the groups the LEDs will be connected in parallel with a resistor each.
This is the basic cabling for one LED. There are two pin headers for power (top=GND, botton=5V) and one pin header for the control pin of the Arduino. Three of the LEDs are connected to one MOSFET with common 5V. The build process is documented in the following pictures:
Resistors first, then the cables to LED’s anode (red cabling).
Then solder the MOSFETs, the pin headers for the control pins and the pin headers for GND in place (I took 2 here which was a good decision in the end. I will explain that later). If you have a closer look at the picture above: do you see what’s wrong? Post it in the comments… Always double-check before soldering!
On the right side is another pin header (also 2 pins here) for the 5V power. Above are the black cablings from the LED’s cathodes. The lower part is for the white LEDs for the mirror ball. I messed up with one resistor so I had to solder a third one… Here the cabling is a bit different because I wired them directly to pins 9 and 10 of the Arduino. I also messed up with the black cable: it goes to the LED’s anode, not cathode so I used yellow cabling to the anode to be reminded of the mistake. It helped! And finally some hot glue to hold everything in place (that is a whole lot of cables…)
Here is a picture to give you an idea of the mess of cables (LED rings are also included there):
I used tape to hold the cable pairs together and marked them to see which is connected to which MOSFET. Also a good idea!
To put them into the spots I had to drill a hole in the spot itself. I think it was a 4mm drill that was perfectly fitting. After that I put some heat shrink tubing in place:
Putting the cables through and adding another small heat shrink tubing to the black wire:
Then I soldered the LED in place:
Always test after sodlering and before shrinking the heat shrink tubes:
Then put the LED into the spot and use hot glue to hold in place:
Last but not least put them on the rod (more on that in a future post):
In the following picture you can see one of the spot LEDs for the disco ball. They are just hot glued into the side walls:
And it’s always a good idea to prepare for mass production:
The control of the lights will be described in the software wrapup. Next week will be about the disco ball, including the control of the stepper motor.