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Chapter 03

Circuitry for the Propeller PCB

Page 7

Some concepts about colours

Previously to get Red colour CC_R was made 0, it seemed like a negative logic. By introducing three "NOT Gates" in the colourCode bits, it will be much easier to imagine about colours. Now to get a Red colour CC_R=1, easy to remember.

NOTE: Though it will introduce an undesired delay. The propagation delay of TTL inverter IC, let us say 22ns (worst: 10-micro second depending on selection of IC) We will have to deal with it later.



Using three LEDs (R, G, B) and two states (ON, OFF):
2 states raise to 3LEDs = 8 colour combinations can be made
( 2^3 = 8 )

Example If Red and Blue LEDs are glowing nearby, they will produce a visual effect of Magenta color. The IC manufacturers, house the three LEDs in the same package.


THE RGB LED

The following picture shows a RGB LED.

NOTE: The polarity mark differ for LEDs of different models, manufacturers. It may NOT always indicate a cathode for Blue LED. Please consult the datasheet of the LED or test it practically with the multi-meter. The continuity/diode-testing mode can be used to test the LED for polarity. It applies a very small voltage to the LED and it starts glowing if the probes at placed in the right polarity.

0	BLACK	All OFF
1	BLUE
2	GREEN
3	CYAN	(G + B)
4	RED
5	MAGENTA	(B+ R)
6	YELLOW	(G+ R)
7	WHITE	(R+ G+ B)

The eighth permutation is BLACK (all LED’s OFF)


colorChart for BGR:


Difference between RGB and BGR colourCode:

RGB	BGR
Decimal colourCode R G B 0 Black 0 0 0 1 Blue 0 0 1 2 Green 0 1 0 3 Cyan 0 1 1 4 Red 1 0 0 5 Magenta 1 0 1 6 Yellow 1 1 0 7 White 1 1 1	Decimal colourCode B G R 0 Black 0 0 0 1 Red 0 0 1 2 Green 0 1 0 3 Yellow 0 1 1 4 Blue 1 0 0 5 Magenta 1 0 1 6 Cyan 1 1 0 7 White 1 1 1

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