This project combines a whole heap of modules to enable a Raspberry Pi to power a large 1.2 inch 4 digit 7 segment display. A small switch switches the display between showing the temperature and the current time. The project uses a real-time clock (RTC) to ensure that the Pi always has the correct time, even if it is not connected to the Internet.
The RTC will allow a Raspberry Pi to know the time, even when not connected to the Internet. As such it is not essential to this project if your Raspberry Pi is going to have an Internet connection.
The diagrams show GND connections in blue, +5V in red and +3.3V in purple.
The I2C bus connections use orange wire for SDA and yellow for SCA.
You may also like to look at separate tutorials for the RTC http://learn.adafruit.com/adding-a-real-time-clock-to-raspberry-pi and temperature sensor http://learn.adafruit.com/adafruits-raspberry-pi-lesson-11-ds18b20-temperature-sensing
When everything is assembled, you can connect the ribbon cable to the GPIO connector. Remember to have the red or white band of the ribbon cable towards the SD card on the Raspberry Pi.
Your Pi will need to be running the latest version of Raspbian. This tutorial was written using Raspbian Buster (July 2019). Checkout our guide for Preparing an SD Card for your Raspberry Pi if you have not done so already. After the installation is complete be sure and run the following commands to make confirm your installation packages are up to date.
sudo apt-get update -y sudo apt-get upgrade -y sudo apt-get dist-upgrade -y
Run the following command to install the adafruit_blinka CircuitPython Libraries.
pip3 install adafruit-blinka
You'll need to start by enabling support for the DS18B20 1-Wire subsystem.
Visit this page for instructions on using raspi-config to enable 1-Wire support.
sudo raspi-config <Interfacing Options> <1-Wire> Enable/Disable <Back> <Finish>
Our clock and 7-segment display work using I2C bus which the Raspberry Pi supports, but it needs to be enabled. This page has step by step instructions. Enabling I2C is almost an identical process as enabling 1-Wire except that a reboot is required and we want to make sure to install the optional packages to scan the bus.
sudo raspi-config <Interfacing Options> <I2C> Enable/Disable <Enable> <Back> <Finish> sudo reboot
lsmod | grep -i i2c
Now that our Pi has rebooted we can confirm that the correct I2C modules have loaded with the following command.
sudo i2cdetect -y 1
This shows that two I2C addresses are in use – 0x68 and 0x70.
Note that if you are using one of the very first Raspberry Pis (a 256MB Raspberry Pi Model B) then you will need to change the last digit of the command port 1 to port 0.
The software for this project uses the Adafruit code for driving the 7 segment display.
pip3 install adafruit-circuitpython-ht16k33
The main loop simply checks the position of the switch and then either displays the temperature or the time.
# SPDX-FileCopyrightText: 2019 Mikey Sklar for Adafruit Industries
#
# SPDX-License-Identifier: MIT
import glob
import time
import datetime
from adafruit_ht16k33 import segments
import board
import busio
import digitalio
switch_pin = digitalio.DigitalInOut(board.D18)
switch_pin.direction = digitalio.Direction.INPUT
switch_pin.pull = digitalio.Pull.UP
# Create the I2C interface.
i2c = busio.I2C(board.SCL, board.SDA)
# Create the LED segment class.
# This creates a 7 segment 4 character display:
display = segments.Seg7x4(i2c)
base_dir = '/sys/bus/w1/devices/'
device_folder = glob.glob(base_dir + '28*')[0]
device_file = device_folder + '/w1_slave'
def read_temp_raw():
f = open(device_file, 'r')
lines = f.readlines()
f.close()
return lines
def read_temp():
lines = read_temp_raw()
while lines[0].strip()[-3:] != 'YES':
time.sleep(0.2)
lines = read_temp_raw()
equals_pos = lines[1].find('t=')
if equals_pos != -1:
temp_string = lines[1][equals_pos+2:]
temp_c = float(temp_string) / 1000.0
temp_f = temp_c * 9.0 / 5.0 + 32.0
return temp_c, temp_f
def display_temp():
temp = read_temp()[1] # F
# temp = read_temp()[0] # C
display.print(int(temp))
def display_time():
now = datetime.datetime.now()
hour = now.hour
minute = now.minute
second = now.second
clock = int('%i%i' % (hour,minute)) # concat hour + minute
display.print(clock)
# Toggle colon when displaying time
if second % 2:
display.print(':') # Enable colon every other second
else:
display.print(';') # Turn off colon
display.fill(0)
while True:
if not switch_pin.value:
display_temp()
else:
display_time()
time.sleep(0.5)
We can easily copy this code onto our Pi's home directory using the 'wget' command and run it using the following python syntax.
cd wget https://raw.githubusercontent.com/adafruit/Adafruit_Learning_System_Guides/master/Large-Pi-Based-Thermometer-Clock/thermo_clock.py
The thermo_clock.py script will not output anything when run, but what you should see is the time or temperature on the large 7-segment display. Using the slide switch should switch modes between time and temperature.
python3 ./thermo_clock.py
The temperature display can easily be changed from displaying degrees F to degrees C by swapping comment line in the code.
temp = int(read_temp()[1]) # F # temp = int(read_temp()[0]) # C
To swap, just move the # in front of the line that does not apply.
This guide was first published on Apr 03, 2013. It was last updated on Mar 26, 2013.
