Step 19: Create Knob Backlights (optional)
* 45 pcs SMD LEDs (1.5x3.0mm) (Red Water Clear Kingbright Standard SMD LED) (Mouser 604-APL3015SRCPRVF01
* a roll of enamelled copper wire (.35mm diameter) (e.g. Reichelt CUL 35
* a roll of standard electric insulating tape
* your favourite soldering equipment
* a soldering "helping hand" tool
* SMD calipersWarnings:
This is a time-intensive task. It is only required if you have non-opaque knobs (like the transparent waldorf knobs), that can be illuminated via backlights. Also, I highly recommend to not enjoy excess caffinated beverages, because, ehm... the LEDs are small :-). As I started, I needed over 20 minutes per "LED Loop", in the end around 10 minutes... and there are 15 of them...
Otherwise, it is very meditative and great training for smd soldering, so... lets begin :-).
First of all, I consulted a few people more firm in electronics than myself, and also read up on some tech resources... On each rotary encoder three LEDs should be mounted and wired in series for easier cabling... Normally, resistors in series to a LED are employed to limit the current that flows, because LEDs are not "linear" in current consumption... a very slight voltage increase leads to a dramatic increase in current... potentially over the limit and "burning" the LED.
In this case, every LED only gets 1/3 of 5V, which leads to very moderate current consumption which I measured with a multimeter. Assuming the 5Vs are stable, nothing bad happens to these LEDs.
This may vary when you employ different LEDs. Even if you use the same, always measure the current that flows, and verify that it is below the datasheet maximum. In many cases, 5V may not be enough to light three LEDs in series. You can then take +9V from the baseboard, but must then employ a resistor that matches your LEDs. In normal cases, please use a resistor and measure the current. I cannot take responsibility for burnt "direct-driven" LEDs.
In fact, nILS takes all responsibilities :-).Description:
* Use the enamelled copper wire, connect it to the +5V at the CS corner connector and wrap it around all encoder housings, like a telegraph line :-). Be aware that your wire stays clear of any holes in the CS - the standoffs must be free and not "collide" with your copper wire (photos 1 + 2).
* Use one layer of insulating tape to cover the encoder shafts - you need to split it in half to have the correct height (photo 2).
* Prepare a copper wire loop, by just wrapping a length of enamelled copper wire around an encoder shaft. Tin the loop at 120 degree intervals (photo 3). (You may need to have your soldering iron at a temperature higher than 400°C to melt the lacquer).
* Cut the wire at your solder points - if nothing went wrong, e.g. one of these frequent reality bugs occured, you should have four shorter wires :-) - use a "helping hand" to solder the SMD LEDs and the wire pieces one by one, see photos 4-6.
* Create a "standoff loop" that guarantees clearance from the encoder base (photo 7)
* Connect the "LED Loops" as shown in photo 8 - one encoder pin is always grounded - make sure you choose the right one. Connect the other end of the loop to your "supply voltage line".
* The LEDs should be really close to the encoder axis, otherwise they won´t "shine through" the relatively small holes in the frontpanel. You can bend the wire to force them into positions, where they are most effective - very close to the axis and quite at the bottom of the shaft.
* When everything is ready your result could look like photos 9+10. Enjoy :-)
* A SMD caliper is highly recommended for this task. Best investment ever for SMD tasks :-).
* The SMD LEDs have markings for their negative pin, for example a color dot. Be sure to align all three LEDs in the ring in the same direction.
* It is not necessary to use a special SMD soldering tip - I used my standard 1.6mm flat tip which worked great.
* SMD LEDs burn quite quickly when you are careless with your soldering iron. Be sure to buy a few more than 45, because it is quite likely that you will lose some.
* My friend jojjelito just informed me, that the SMD work can be avoided in two ways:
a) use axial LEDs like these from digikey
(lumex opto SSL-LXA228SGC) - they are a little bit more expensive but that will easily be compensated by the time saved.
b) use a transparent washer and glue LEDs to the side of it - you will obtain a nice area light. Nice tricks, thanks! :-)
* Also, Wilba just used normal "through-hole" LEDs, that were connected to GND and a supply line and then bent very close to the axis.
* Lastly, Altitiude recommends using a LM317 + fixed resistor + trim potentiometer (look in the datasheet for a connection example) to be able to dim the backlight brightness. This is a very good idea, as it allows to adjust your LEDs to the optimum current draw.
Edited by Hawkeye, 01 July 2011 - 01:38.