Connect 5V sensor to 3.3V microcontroller

Hello all,

For my bachelor thesis I need to use a microcontroller and a micro force sensor:

FT-S100 and FRDM – KL25Z

The sensor uses 5V and the GPIO from the board is 3.3V, how can I most optimally use the combination of those two features? I have seen it is possible to use a voltage divider but the fact that this will reduce the accuracy will be very bad so I really need a better solution.

Kind regards,
Lisa Meijer

Using a voltage divider with precision resistors will not reduce the accuracy significantly, and you can compensate for most of that error in software. You will want to pick the values for the resistors carefully. If you pick values that are too low you will load the output driver on the FT-S100 and reduce accuracy. If you pick values that are too high, you will limit the frequency response at the ADC input and possibly introduce other ADC errors.

If you want to be safe, use reasonably high values for the divider resistors (100K ish) and then use a unity gain precision opamp between the divider and the ADC input. Watch out for the voltage noise characteristics of the chosen opamp, I assume the signal from the sensing probe will be low frequency (

You can use a level shifter.. Something like a MOSFET, BSS138.. here is a diagram http://cdn.sparkfun.com/datasheets/BreakoutBoards/Logic_Level_Bidirectional.pdf.

Usually that would work, but the FT-S100 is has an analog 0-5V output so a digital/logic level shifter won't do the job for her project.