This voltage can be used in a multitude of ways including triggers to comparators and other analog circuits as well. However the objective of this exercise is to have a battery powered smart device and in order to make the design reusable and customisable, we shall employ a Microcontroller. In particular the Texas Instruments MSP430G2553 was used for a number of reasons listed as follows.
1. The MSP430 is cheap and available from a number of sources including TI.com, RSComponents and Element14
2. It has an inbuilt oscillator which reduces the BOM and complexity
3. It can operate at lower voltages ranging from 1.8V to 3.6V
4. The power consumed in the Low Power Modes is very small
5. Its available in the DIP Packaging for prototyping and TSSOP for final designs
6. It can be programmed using Energia which is the TI equivalent to the Arduino IDE which makes it easy to use.
The other features of the MSP430 are listed in the data sheet and Figure 2 shows an excerpt from the same.
Given a 10-bit ADC and a Vcc of 3V set as reference for the ADC, the resolution of the conversion is 3000mV/1024bits or 2.93mV/bit which means that for every 2.93mV change in ADC input, 1 bit will be the change in the final conversion. We shall discuss this further when we begin to customise the ADC Code and will use a different Vref than Vcc.