MAKE LED WASH-LIGHTS.
This is the newer and better version of the LED spotlights. Instead of the 5mm LEDs it uses a group of nine superflux LEDs for greater intensity and smoother mixing. It also uses a manufactured PCB which I've priced at a sensible level. You can buy these in the online shop on this site.
Here are the bare PCB's. No messing about etching them yourself this time, I've had a batch made in China in good quality FR4 laminate with the pads gold plated to ensure easy soldering.
They are designed for making common anode LED arrays, but can also be used for common cathode systems. (see the note at the end).
Here's the schematic. Very simple with the only note being the use of two resistors in the red LED circuit. These are wired in series to reduce their heat dissipation due to the lower forward voltage of the red LEDs.
Let's start by selecting and soldering in the resistors. By a happy coincidence the same value can be used in all four positions to give a close current match between all the colours. For 20mA you can use 100 ohm resistors and for 40mA you can use 56 ohm resistors. In this instance I was using good quality LEDs so I used 56 ohm resistors.
There are some new superflux LEDs available that have three or even five parallel chips in them. Appropriate resistors might be 39 ohms for 60mA and perhaps 27 ohms for 100mA. I'm not sure I'd recommend running the LEDs at 100mA though since the total power dissipation will be quite high and combined with the extra heat from the resistors, LED life may be affected.
Next place the LEDs on the PCB and solder them. The colour of each LED is marked on the PCB and there is a chamfer on one corner of the LEDs that should line up with the chamfer shown on the PCB graphic.
Apparently some of the Chinese Ebay suppliers are shipping LEDs with reversed polarity, so before you solder all your LEDs in it is well worth checking that the polarity chamfer does indicate the negative side. You can either use a 9V battery and a resistor, or get a dedicated LED tester which is available quite cheaply on the Internet.
You can either solder the LEDs in individually by hand or use a standard assembly frame as shown above. Soldering one leg on each LED before moving onto the next will lower the risk of LED heat damage while soldering.
The PCB is RoHS compliant which means it can be used with lead free solder, but I strongly recommend the use of lead based solder since it produces a much better electrical and mechanical connection.
Once all the LED pins are soldered you can add wires. I used pink for the common positive and red, green and blue wires for their respective colour. The pads are marked on the PCB as R, G, B and ++ in raised track under the black solder resist.
A cable tie at the back of the PCB helps keep the wiring neat and also lowers the amount of wire movement at the pads when the PCB is handled.
Then test on a regulated 12V supply with the positive connected to the common wire and the negative touched to the red, green and blue wires in turn to test each circuit of LEDs. Then try commoning all the colours to negative at once and prepare to be dazzled!
The PCB is specifically designed to fit into a standard MR16 downlight frame. This is the frame used for the common 50W 12V halogen reflector lamps that are about 2" (51mm) in diameter.
You can also make single colour panels by using just one colour or even a couple of colours of LED. In this version I've used all blue LEDs and adjusted the resistor values accordingly. One of the red circuit resistors has been replaced with a link in this instance. To make sure all the LEDs light up you will need to common the R,G and B pads.
The use of all white LEDs would make a nice customisable panel for use in low energy solar powered systems.
If you have a controller that requires common cathode LED arrays you can simply install the LEDs in with their corner chamfer pointing to the opposite corner of the one on the graphic and use the ++ pad as the common negative.