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Chapter 03

Circuitry for the Propeller PCB

Page 5

Some concepts about switching

Three LEDs

What will happen if three type of LEDs Red (R), Green (G) and Blue (B) are connected together.
Same onSequence is provided to all:

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Example:

CC serves as the master control.
CC_G = N/C will switch OFF all Green LEDs.

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Example:

CC serves as the master control.
CC_B = N/C will switch OFF all Blue LEDs.

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TDM for RGB LEDs

Reminder: Whenever the "onSequence" is NOT exactly the same for all R, G, B we will use TDM.

Without having separate anodes, the effect of having separate anodes is achieved by TDM

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Example:

It is required to switch the LEDs as sown below. How will you proceed, to produce the desired "End effect" ?


Observation:

1. Find the onSequence (Nibble) separately for R, G, B
2. It is NOT same: Nibble_R = 1001, Nibble_G = 1111, Nibble_B = 0011
3. So we need to apply TDM

CC_R = GND, CC_G = N/C, CC_B = N/C, Nibble = 1001 (Sequence for Red LEDs)
CC_R = N/C, CC_G = GND, CC_B = N/C, Nibble = 1111 (Sequence for Green LEDs)
CC_R = N/C, CC_G = N/C, CC_B = GND, Nibble = 0011 (Sequence for Blue LEDs)

The slow animation shown below, illustrates the concept of TDM for RGB LEDs:

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Question: If it is desired to:
switch ON all Red LEDs,
two middle Green LEDs and
none of the Blue LEDs,
What will be the TDM Cycle ?
( in other words what will be the values of CC_R, CC_G, CC_B and Nibble w.r.t. time )

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Solution :

CC_R = GND  CC_G = N/C,  CC_B = N/C,  Nibble = 1111
CC_R = N/C  CC_G = GND,  CC_B = N/C,  Nibble = 0110
CC_R = N/C  CC_G = N/C,  CC_B = GND,  Nibble = 0000

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