The physical circuit assembled is shown by the figure below!
- PIC16F877A 40 pins;
- LCD Display 16x2 8 bit connection;
- 4 MHz oscillator crystal;
- 22 pF ceramic disc capacitors.
- TIMER0 Module;
- TIMER1 Module;
An Assembly source code was developed to establish a communication protocol between the sensor module DHT22 (AM2302) and the PIC16F877A Microchip microcontroller. The reading values are displayed on an LCD display, connected to the microcontroller throught an 8 bit connection, as shown by the figure below.
The DHT22 module sensor sends the reading values after a 18ms low level signal sent by the microcontroller. The figure below shows the start signal sent by the microcontroller (orange line), followed by sensor response (blue line), which starts with two alternating bits of 80us each.
After that, the reading values are sent by the sensor as 16-bits numbers in a 40-bits set, which contains the relative humidy, temperature, and an 8-bit number for checksum, respectively.
The figure below shows the bit sequence sent by the sensor, as well as the division of bytes.
The developed program reads the sent bytes through the logic represented by the flowchart in the figure below.
