Analog-to-Digital Converter Module (A/D)
Microcontroller can only understand 0 and 1. In order to make the microcontroller understand the
external signals which are usually fundamentally different from it understands, the signals have to be
converted. An analogue to digital converter is an electronic circuit which converts continuous signals
to discrete digital numbers. This module is used for input pin voltage measurement (analogue value).
The result of measurement is a number (digital value) used and processed later in the program. [8]
Microcontroller PIC16F690 has built in 10-bit Analog-to-Digital Converter module (A/D). 10 bits
resolutions amount to 1023 binary. With its reference voltage, obtain the output voltages from sensor's
working circuit.
Add an Analog to Digital Converter (ADC) between the sensing element (SnO2) and the load
resistance (RL) as shown in Figure 6, so that the measuring circuit can convert the changes in the gas
sensor’s conductivity affected by the concentration condition to an output voltage signal, and at last
obtain the concentration information.