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Charlieplex driver


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I am thinking of making another board, high current Charlieplex driver.

My idea is to have two 595s and 24 transistors (I am planning on using BC807DS so the actual number will be 16.)

Supply voltage 3.6V, base resistors 2k2, segment resistors 22-56ohms.

One thing I am missing is a protection circuit. I want to use 74HC123 which would be triggered by latch.

This is what I have so far:

 

post-197-135135507037_thumb.png

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LEDs. Forward current will be much higher than maximum current, which is OK because of the duty 12.5% cycle. When shift registers are not refreshed, for example during debugging, this high current could damage LEDs.

123 will enable shift register's outputs for a short period of time when triggered by latch and will be re-triggered by the next latch, and so on. As long as latch pulses are present, LEDs are on. The only scenario not covered by this protection is software mistake that will select same column/row each time.

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