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This question already has an answer here:

I have some analogue signals between 0 and 5 Volts being fed from a multiplexer into another board that only accepts signals up to 3v3.

Simple Diagram

What is the best way to step down the voltage?

The signal doesn't need to be very precise (It is going to be used to select one of 32 options depending on which range of values it falls under and will be a fixed value) and doesn't need to be updated often (User is only likely to change the value two or three times during operation)

I was thinking of just using a 3K3 Ohm x 2K2 Ohm voltage divider with precise tolerances but I wonder if anyone can foresee any problems with this or can recommend a better method?

How should I link my analogue reference? am I going to run into problems if I just use another identical divider to jump the 5V rail down?

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marked as duplicate by MCG, winny, Marcus Müller, laptop2d, Bimpelrekkie Aug 14 '18 at 11:54

This question has been asked before and already has an answer. If those answers do not fully address your question, please ask a new question.

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    \$\begingroup\$ Use a level shifter \$\endgroup\$ – MCG Aug 10 '18 at 12:53
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    \$\begingroup\$ If the signals are truly analouge, then you should use a voltage divider with two resistors. \$\endgroup\$ – Lundin Aug 10 '18 at 12:57
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    \$\begingroup\$ @Lundin -- yes, once you are sure there are no issues with changing loads. \$\endgroup\$ – Scott Seidman Aug 10 '18 at 13:02
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    \$\begingroup\$ 3K3 Ohm x 2K2 Ohm voltage divider is fine, but it's input impedance might be too low in relation to the output of the device feeding it. Put a buffer amplifier before the voltage divider and then the input impedance is high. \$\endgroup\$ – D Duck Aug 10 '18 at 13:04
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    \$\begingroup\$ Or perhaps you need a buffer amplifier after the divider. If, or where, it is needed can't really be known without the details of the systems. \$\endgroup\$ – Chris Stratton Aug 10 '18 at 15:03
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Just be careful about the "target", impedances and frequencies involved. As an example, if the target system is an ADC input, it would prefer also a buffer capacitance (without resorting to a voltage follower, if precision required isn't too much), just to avoid that on voltage sampling transients the input resistors cause a drop.

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If you're also planning to derive the analog reference from 5V, you may want to consider dividing your analog signals and the reference by two (using two identical resistors, with a target range of 0 to 2.5V. Resistors from the same batch usually have very close values, so dividers by two are inherently more precise.

Regarding signal conditioning, I would start with a simple resistor divider, and add a unity gain amplifier if the load effects are significant.

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With your requirements is enough just using a resistor divider without any problem.

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