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OPTIONAL PERIMETER LED INSTALLATION INSTRUCTIONS:
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On keyboards with translucent plastic enclosures, up to 6 LEDs may be installed at fixed
locations around the perimeter of the keyboard's printed circuit board. However, doing so will require a soldering
iron, solder and wire cutters. A digital multi-meter (DMM) or continuity test isn't necessary but could be helpful
if you already own them. If you make a mistake, you will also need a solder removal tool and needle nose pliers.
Finally, you must also buy your own LEDs.
Which LEDs do we use or recommend and where can I buy them? Unfortunately the ones we use aren't available to
individual consumers. Do we sell the LEDs to our customers? No, because we would have to charge you $10 just to
cover our costs. Why don't we just include them with the keyboard? Then we would have to charge those customers
who don't want the perimeter LEDs the cost of these LEDs. Therefore we will leave selling electronic components
to the experts who can do it efficiently; the buying of the peripheral LEDs to those who want them, and we will
stick to manufacturing keyboards.
Here are the characteristics of the T1 or 3mm package LEDs we use:
- Red: Forward voltage = 1.8V at forward current of 20mA; 500mc luminous intensity; 30 degree viewing angle.
- Yellow: Forward voltage = 2.3V at forward current of 20mA; 2000mc luminous intensity; 30 degree viewing angle.
- Blue: Forward voltage = 3.4V at forward current of 20mA; 2600mc luminous intensity; 30 degree viewing angle.
- Green: Forward voltage = 3.2V at forward current of 20mA; 3800mc luminous intensity; 40 degree viewing angle.
Please note that TG3 drives these LEDs at around 5.25mA maximum, but LEDs are commonly specified at 20mA.
As you can now see, the current and voltage characteristics of LEDs vary with color. They also even vary between
manufacturers and part number for LEDs that are the same color. Therefore your perimeter LEDs may not "track" the
factory installed backlighting LEDs with regard to turn-on thresholds and luminance intensity at any given brightness
level. You can still use LEDs with slightly different current and voltage ratings, and lower luminous intensity -
they will still work but may not be as bright or "track" as well.
We recommend that these perimeter LEDs be installed on the bottom-side of the printed circuit board (PCB). Installing them
on the topside will result in very bright "hot spot" points of LED light because the housing plastic allows more light
to pass through then the keycaps. The location of these 6 LEDs is shown in Figure 1. Be careful of clearance between
the bottom pan and the bottom of the printed circuit board - especially for LEDs DS28 and DS29. The LED package should
be either T1 or 3mm to match the lead spacing of the PCB. LEDs are also "polar devices". This means that they can be
installed in the wrong way that will cause them not to work. LEDs have "anodes" (positive terminal) and "cathodes"
(negative terminal). The cathode should be installed in the square shaped solder pad on the PCB; the anode should be
installed in the circular pad. Failure to install the LEDs with the proper polarity is the most common cause of the
LEDs not lighting.
The perimeter red and yellow LEDs must be installed in pairs as shown in Table 1 and Figure 2 per the factory installed
resistors. Referring to the schematics shown in Figure 2, the red and yellow LEDs are installed with two of them
"in-series" in order to reduce the overall current consumption of the keyboard. The blue LEDs are installed
"in-parallel" because the sum of the forward voltage drops is 6.4V - that exceeds the +5V power supply, so the blue
LEDs would not turn-on if wired with two of them "in-series". TG3 has already factory installed the resistors shown
below in Table 1. These values are for "typical" LEDs of their corresponding color.
Can a different color perimeter LEDs be installed (for example, yellow perimeter LEDs on a red backlit keyboard)? Yes,
again we recommend followings the guidelines in Table 1 and Figure 2. Depending on the color of the keyboard
backlighting and the color of your chosen perimeter LEDs, resistors may also need to be removed and changed with
ones of different value. In other situations, resistors may be removed and not replaced (for example, adding blue
perimeter LEDs to a red or yellow backlit keyboard). All resistors should be 1/8 Watt or greater and have a
tolerance of 5% or better.
Can a mixture of colors be used for the perimeter LEDs? Yes, but again we recommend followings the guidelines in Table 1
and Figure 2. We further recommend that you adhere to the rules regarding keeping the red and yellow LEDs in pairs
(i.e. DS24 & DS26, DS28 & DS29, DS25 & DS27). This also insures that the LEDs will "track" each other with regard
to turn-on thresholds and luminance intensity at any given brightness level.
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