# Multiplexer Question

**URL:** <https://boards.straightdope.com/t/multiplexer-question/215375>\
**Category:** Factual Questions\
**Created:** [November 26, 2003, 2:04pm UTC](https://boards.straightdope.com/t/multiplexer-question/215375 "2003-11-26T14:04:04Z")\
**Posts on this page:** 5\
**Page:** 1

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**Author:** ![Munster](https://avatars.discourse-cdn.com/v4/letter/m/41988e/32.png) [@Munster](https://boards.straightdope.com/u/Munster)\
**Post date:** [November 26, 2003, 2:04pm UTC](https://boards.straightdope.com/t/multiplexer-question/215375/1 "2003-11-26T14:04:04Z")

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I am in the process of designing my final year project in college and need to select between two analog signals.

To this end I was thinking that I should use a mutiplexer.

I was wondering if I could use a regular digital MUX or would I have to use an analog MUX.

Also if anyone is familiar with electronics workbench/multisim do they know of an analog MUX in the parts library.

Thanks.

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**Author:** ![scr4](https://avatars.discourse-cdn.com/v4/letter/s/59ef9b/32.png) [@scr4](https://boards.straightdope.com/u/scr4)\
**Post date:** [November 26, 2003, 3:21pm UTC](https://boards.straightdope.com/t/multiplexer-question/215375/2 "2003-11-26T15:21:30Z")

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If you are trying to multiplex analog signals, you definitely need an analog multiplexor. Digital devices only accept and output digital signals; they won’t preserve input voltage.

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**Author:** ![Munster](https://avatars.discourse-cdn.com/v4/letter/m/41988e/32.png) [@Munster](https://boards.straightdope.com/u/Munster)\
**Post date:** [November 26, 2003, 3:42pm UTC](https://boards.straightdope.com/t/multiplexer-question/215375/3 "2003-11-26T15:42:10Z")

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Cheers for that.

Now that I think about it using a digital MUX would only flip the output between Vcc and GND.

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**Author:** ![RGillen](https://avatars.discourse-cdn.com/v4/letter/r/848f3c/32.png) [@RGillen](https://boards.straightdope.com/u/RGillen)\
**Post date:** [November 26, 2003, 3:56pm UTC](https://boards.straightdope.com/t/multiplexer-question/215375/4 "2003-11-26T15:56:44Z")

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I am not familiar with Multisim, but look in you parts library for a 74x4051, 4052, or 4053. These are some basic discreet analog MUXes.

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**Author:** ![bughunter](https://avatars.discourse-cdn.com/v4/letter/b/aeb1de/32.png) [@bughunter](https://boards.straightdope.com/u/bughunter)\
**Post date:** [November 26, 2003, 6:05pm UTC](https://boards.straightdope.com/t/multiplexer-question/215375/5 "2003-11-26T18:05:40Z")

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If you’re in a pinch for parts and don’t need super high off-channel rejection, then you can use an op-amp in a noninverting summing configuration (fig 3.18 of H&H’s The Art of Electronics), and FETs in series with the input resistors. Drive the FETs with complimentary op-amp comparators so that only one is switched on.

You can build an N-to-1 analog mux this way, if you have a way to activate each FET exclusively. Just remember that the off resistances of the FETs are still finite, so you will get some crosstalk at the output. Choose FETs with very low off conductances.