led Arduino multiplexing help needed

Posted on Feb 6, 2014

If you want to build a 7 to 128 demux with 3-to-8 and 4-to-16 demuxes, then put the 3 high bits of your output address into the 3-to-8, and use the outputs of that as the input enable to the individual 4-to-16 demuxes (assuming that it has an enable pin), so the output #0 on the 3-to-8 would go to the input enable of the first4-to-16 demux, the

led Arduino multiplexing help needed
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output #1 would go to the second, etc. No other components I can think of, except possibly inverters if the input enable is the wrong polarity. Also check that your demux can source enough current to power the LED, if not then you may need to use a transistor to boost the current. @SamuelPogue Tim May 2 `13 at 23:43 I am attempting to simulate this using CDS using a 74LS138 as the 3-to-8, and 7 74HC154`s for the 4-to-16`s. I have it set to where SPDT`s represent the address outputs on the arduino where one lead is connected to Vcc, and the other is connected to digital ground. However something is going wrong here and the LED`s won`t light. Because I have all the anodes of the LED`s soldered together, and the cathodes have to be the ones to connect to the outputs of the 4-to-16`s, I am assuming I am doing something wrong with the Enables. Of course, I am trying to discern why there are multiple Enables. Samuel Pogue May 3 `13 at 20:42

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