mattg31 wrote: ↑
Mon Apr 16, 2018 1:30 pm
I'm using this:https://www.sparkfun.com/products/12642
And it states it works better (more stable outputs) with a 5v VCC. However this means the analog output will be in the 5V range, which is a problem for my ADC.
My plan is to just use a 3.3v zener diode on the output. Does that sound reasonable?
Using a zener will 'work' but will cause clipping of all the signal information above 3.3V.
A voltage divider will give some signal loss but will be a lot simpler over an active circuit.
The formula you want to work with will be Vout= Vin(R1/(R1+R2). The ratio of R1 to R2 would be 1K (R1) to 2K(R2). R1 and R2 would be wired in series; with the top of R1 being the input analog signal, the connection point of R1/R2 (Vout) will be the input to the ADC and the bottom of R2 would go to the common ground.
Consider the ADC input impedance. Using too low of an R1/R2 value could fall outside of a impedance range of the ADC.
When you have selected the physical resistors (1%) ohm them out and use their actual metered measured values in the formula; to check that the R1/R2 junction will not exceed 3.3 volts with the supplied resistor values.
You might, also, consider a good quality small value cap attached from the R1/R2 junction point to the input of the ADC.
Without knowing why you are deleting my postings, I will not know how...