24 channel ADC Level shifting

[NivagSwerdna]

As part of my tinkering I would like to be able measure the voltages across 16 address lines and 8 data lines in a vintage 5V system. I am considering a 3.3V uP that has lots of analog inputs but only 3V3 tolerant.
My sample rate requirement is very low as this is for static analysis.
It seems a traditional approach is to use an op amp for the level shift but that's a lot of op amps! Is there a more dense approach? Maybe an analogue switch and multiplex?

Thanks in advance

[Dabbot]

Op amps are also cheap. I'm assuming you want to maintain a high impedance, otherwise I suggest a simple resistor divider on each channel?

5V line
22K
ADC channel
33K
GND

[Brutte]

You need a 5v analog multiplexers and then one opamp that will do antialiasing + offset + gain. I think you can control that all with 10-pin uC.
If you intend to sample all lines at "the same time" then that could be a bigger problem but if you can make sure no signal transition takes place during sampling channels then that is quite easy.

Alternatively, if you just need logic levels of the lines, why not use 5V latched shift registers? These are also cheap as dirt.

[Zero999]

If the bandwidth is low and the inputs aren't especially high impedance, then a potential divider should do the trick. A capacitor will need to be connected to the ADC input, to provide a low AC impedance to the sample and hold circuit.

[LapTop006]

It seems a traditional approach is to use an op amp for the level shift but that's a lot of op amps! Is there a more dense approach? Maybe an analogue switch and multiplex?

If you only care about digital data you could just use comparators, or (losing some accuracy around level transitions) even a buffer that's ok with an input voltage above Vcc, random example from a few minutes of trawling Digikay 74HC7014 (at least the Nexperia version, with current limiting resistors), or CD4050 (TI).

[NivagSwerdna]

Thanks for the suggestions... I think I might need to rethink my requirements.