# Electrical – Analog to digital conversion with variable VCC

adcanalog

I would like to build a circuit of a microcontroller reading an analog accelerometer, without the use of a voltage regulator. The problem would be that the battery's voltage will gradually decrease with time changing the VCC of the accelerometer and microcontroller.

In this case, the obvious problem when finding the step for the analog to digital conversion:

$$step = \frac{VCC}{1023}$$

Is that the step is dependent of VCC and will change with it.

Is it possible to do analog to digital conversion with variable VCC?

(The accelerometer is the ADXL377)

#### Best Answer

The ADXL377 has an output that is ratiometric to its supply voltage. Read the data sheet on page 3 and look at note 2 at the bottom of the page.

This means you are in-luck because if the output voltage goes down by 10% due to Vs dropping by 10% then 1 LSb of the conversion remains exactly equivalent to the value of acceleration implied by the device.