• Name: PIC12F675 Temperature display.
• Description: Displays the temperature and humidity readings from a DHT11 sensor to a single seven segment LED module driven by a 74HC595 shift register. Written in C code.
• Author: Gavin Lyons.

• Overview
• Features

In this folder the source code in C can be found in file dht11_12.c.

This program displays the temperature and humidity readings from a DHT11 sensor to a single seven segment LED module driven by a 74HC595 shift register. Written in C code.

The information is displayed in a scroll like fashion thru the single digit display. with a second between each display.

Program flow

1. start
2. display b (Begin)
3. wait two seconds for sensor to stabilize
4. Get data from sensor.
5. display b (Begin)
6. Display t (t for temperature)
7. Display first digit of temperature reading i.e 1 for 19 C
8. Display second digit of temperature reading i.e 9 for 19 C
9. Display H (h for humidity)
10. Display first digit of humidity reading i.e 3 for 38 %
11. Display second digit of humidity reading i.e 8 for 38 %
12. GOTO to 4

Error codes

1. E = Comnmunications Error. No response to the PICs request signal from sensor.
2. Dash = Communications Failure. Sensor responded to Start signal but failed to communicate data with PIC correctly.
3. C = Checksum Error. Received all data from sensor but it failed checksum.

Communication Format with DHT11 can be separated into four stages.

1. Request to sensor
2. Response from sensor
3. Data Reading 5 bytes from sensor
4. Sum the 1st 4 bytes and check if the result is the same as CheckSum(5th byte)

GPIO function

GPIO function on PIC, 3 lines to 74HC595

1. SER Serial / Data in pin 14 GP0
2. RCLK / Latch pin 12 GP1
3. SCLK / storage clock pin 11 GP2
4. n/c
5. DHT11 sensor line. GP4
6. n/c

Connections from seven segment single module to shift register pins.

1. A = pin 7 QH
2. B = pin 6 QG
3. C = pin 5 QF
4. D = pin 4 QE
5. E = pin 3 QD
6. F = pin 2 QC
7. G = pin 1 QB
8. Dot n/c

For more info on pinlayout of seven segment display, see here.

https://en.wikipedia.org/wiki/Seven-segment_display

For more info on DHT11 sensor see datasheet here.

https://components101.com/sites/default/files/component_datasheet/DHT11-Temperature-Sensor.pdf