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I have an arduino mega and 256 analog sensors that I have to read. I already did it with a lot of 4067 16:1 multiplexers. At first it took all of my pins. Then I paralleled the multiexers to use only 4 digital pins to Control them and played with the E of them to turn them on or off.

Now my question is : is there a 256 : 1 multiplex that operates in the 5v range so my mega can handle it (or even smaller arduino) or if not a 128:1,64:1, 32:1. In order to make my board simpler.

Thank you very much for your time reading this. Have a nise day.

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  • \$\begingroup\$ other microcontrollers than the atmega have multiple ADC channels (8 is pretty common, typically realized through an integrated mux). So, by switching to a less expensive platform than Arduino, you could also reduce your hardware complexity by a factor of 8. Depending on the bandwidth of your 256 signals, an array of ADCs and a few shift registers or digital muxes might be way easier than external analog muxing. It all depends on your signal! \$\endgroup\$
    – Marcus Müller
    May 1, 2021 at 11:28
  • \$\begingroup\$ Do you actually need analog multiplexers, or are you looking for digital levels? The ATmega2560 has 16 ADC channels. What is the input range of your signal? \$\endgroup\$
    – Reinderien
    May 1, 2021 at 17:18
  • \$\begingroup\$ What if I used 2 16:1 multiplexers, 1 for 5v & 1 for gnd, for all of my sensor in a 16x16 matrix. Use 4 digital pins for each mux to control and 1 digital pin to set high for the 5v mux and low for the gnd mux. So every time I have only one sensor powered and provide to A0 data. This is 10 digital & 1 analog. Even an uno could do that. Should I use any diodes? Is my thinking correct? Am I missing something? \$\endgroup\$
    – Thanasis Valto Kourpetis
    May 4, 2021 at 8:14

2 Answers 2

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You can use 3 pins (2 with some cleverness) to control a 74HC595 shift register. The shift register has 8 bits, which is sufficient to address 256 inputs.

You would feed 4 bits to 16 74HC4067 or similar and the other 5 bits to a 1 low of 16 decoder, such as 2x 74HC138, and use those outputs to enable the '4067 chips.

There are serially controlled MUX chips such as the 32:1 ADG731 32-input chip however they are higher performance, sometimes better protected, and tend to be more expensive (and perhaps may suffer from availability issues in the future). To use the required 8 chips you could use a 74HC138 as the selector. You'd need the three address pins plus the 2 + 1 SPI pins for a total of 6 pins.

As a rough comparison, USD Digikey price for Q100 each of the first solution is $8.28 vs. $89.40 for the second. Or if you prefer LCSC, $3.17 for the first one.

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  • \$\begingroup\$ Makes sense. The series impedance might be an issue to the OP. But who knows given the lack of specs and the fact that a 74HC4067 is already stated as acceptable. So I'd guess that twice the impedance would also be fine. I'm not sure the OP has a lot of other reasonable options. +1 \$\endgroup\$
    – jonk
    May 1, 2021 at 7:41
  • \$\begingroup\$ @jonk OP didn't even say 74HC. The CD4067 is 5x worse than the 74HC4067 (1200 vs. 225 ohms max at 85°C). \$\endgroup\$
    – Spehro Pefhany
    May 1, 2021 at 7:48
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    \$\begingroup\$ Ah. I guess even that much is unsure from the OP's writing. \$\endgroup\$
    – jonk
    May 1, 2021 at 7:56
  • \$\begingroup\$ What if I used 2 16:1 multiplexers, 1 for 5v & 1 for gnd, for all of my sensor in a 16x16 matrix. Use 4 digital pins for each mux to control and 1 digital pin to set high for the 5v mux and low for the gnd mux. So every time I have only one sensor powered and provide to A0 data. This is 10 digital & 1 analog. Even an uno could do that. Should I use any diodes? Is my thinking correct? Am I missing something? \$\endgroup\$
    – Thanasis Valto Kourpetis
    May 4, 2021 at 8:14
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With microcontrollers available for sub $1 these days, it is not unreasonable to use a number of them vs 1 microcontroller and a large mux. Benefits might be less pcb area, faster acquisition time (as a number of adcs are working in parallel) and redundancy. Downsides might be the need to program (ie load the code into) a number of microcontrollers along with a bootloader etc.

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  • \$\begingroup\$ What if I used 2 16:1 multiplexers, 1 for 5v & 1 for gnd, for all of my sensor in a 16x16 matrix. Use 4 digital pins for each mux to control and 1 digital pin to set high for the 5v mux and low for the gnd mux. So every time I have only one sensor powered and provide to A0 data. This is 10 digital & 1 analog. Even an uno could do that. Should I use any diodes? Is my thinking correct? Am I missing something? \$\endgroup\$
    – Thanasis Valto Kourpetis
    May 4, 2021 at 7:51

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