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Author Topic: Need a powerful multiplexer...  (Read 1139 times)
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Hi everyone.
I was thinking about a nice project that would be interesting to develop: a LED clock. Here's how I imagine it (roughly):


I was wondering if there's a multiplexer huge enough to handle, let's say:
- 1 LED / second = 60 LEDs
- 2 extra LEDs / 5 minutes mark = 24 LEDs
- 4 digits, 9 LEDs high * 5 LEDs width = 27 LEDs
- 1 comma = 2 LEDs
Total: roughly 110 LEDs...
So I need a 7bits multiplexer? a 128++ pins monster? Does it exist?
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I would highly recommend using shift registers. The data rate is going to be very slow, one change per second, and the logic of a shift register is VERY easy with something that is set sequentially like this.
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Could you develop a bit ?
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Look into the TLC5940.  It is essentially a shift-register with built-in LED drivers.
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you could also use normal registers, 74*374, etc.  They need more pins (although this can be reduced using a decoder for the address lines) but are far faster than serial shift registers.
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Wow, I just took a look a the TLC's datasheet, I think this baby's just took complicated for me! But I haven't mentioned that I just have figured out how to handle a SN754410 and didn't succeeded with 74HC4051 smiley-wink
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Wow, I just took a look a the TLC's datasheet, I think this baby's just took complicated for me!

With the Arduino library, it is much easier to use than rolling your own solution.
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You can use several 32 bit ADG731 mux, very easy to interface and you can cascade however many you want.

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