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I need a simple solution to connecting two digital signals to a single physical terminal. One should be normally connected while the other one disconnected while this does not draw any power. Only when the 2nd signal is to be connected and the 1st signal disconnected, the switching circuit will draw power.

I know it is tempting to say that a SPDT relay will do the trick, but I need something much smaller and preferably without moving parts.

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Two input MUX is considered a rather fundamental logic gate and there are plenty of such chips available e.g. 74xx series chips. While those CMOS muxes must be connected to a supply, they draw basically no appreciable power.

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  • \$\begingroup\$ They requirement the selection pins to be held at specific logic levels at all times + they draw around 100uA at all times. As I wrote, I am after a solution that does not draw any power. \$\endgroup\$
    – user733606
    Commented Dec 27, 2021 at 8:17
  • \$\begingroup\$ @user733606 The selection pin (when static) draws more like 1 pA. It is really just a MOSFET gate. It can be easily provided by a 1 MOhm pulldown. Such a mux gate as a whole, when static also consumes essentially no power in total (well under 1 µA). But if you have no access to a logic voltage, then it won't work indeed. \$\endgroup\$
    – tobalt
    Commented Dec 27, 2021 at 8:36
  • \$\begingroup\$ I know that in theory the current consumption should be near 0, however all devices I've managed to find are 50 to 100uA. \$\endgroup\$
    – user733606
    Commented Dec 27, 2021 at 9:11
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    \$\begingroup\$ @user733606 Read the note [1] in the datasheet. This additional supply current in not relevant in a static scenario. It only briefly appears when there is a logic transition at the input, due to shootthrough of the logic transistors. When the inputs are all either at VDD or VSS, then the consumption is extremely small. \$\endgroup\$
    – tobalt
    Commented Dec 27, 2021 at 15:16
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    \$\begingroup\$ @user733606 Beware of the temperature range when reading input leakage current. The data sheet you reference shows input leakage of ±0.1uA max at 25°C; even over the full military range of -40°C to +125°C it is only ±0.75uA \$\endgroup\$
    – user131342
    Commented Dec 28, 2021 at 17:24

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