Circuitry

I have one raspberry pi 4 with only one pin that can read the 1-wire protocol. I have 6 DS18B20 temperature sensors I want to use. It turns out the 1-wire protocol is a bus protocol meaning a single wire can be shared by many devices trying to communicate. All you need to do is connect the dat lines of each sensor as shown in the diagram above.

Notes: I use pin 2 on my pi4 (5v power) and pin 39 (GND) as vcc and gnd.

Code

1. Ensure this line is present in /boot/config.txt

   dtoverlay=w1-gpio
   

   Then reboot

   sudo reboot
   

2. Identify your devices

   ls /sys/bus/w1/devices
   => 28-011939e3f4d8  28-01204e866407  w1_bus_master1
   ls /sys/bus/w1/devices/28-011939e3f4d8
   => ... uevent  w1_slave ...
   

   They will start with 28 then a - and then the serial of your device.
   Mine are 28-011939e3f4d8 and 28-01204e866407.
   The file we will be using is inside this folder and called w1_slave.

3. Read from them
   
   Here’s the script I use to do that. I stole the original from here and modified it to handle multiple devices.
   
   Just modify the array files at the start of the script with your own device serial numbers. The files array can be any length > 1.

    import os
    import time
       
    # Initialize the GPIO Pins
    os.system('modprobe w1-gpio')  # Turns on the GPIO module
    os.system('modprobe w1-therm')  # Turns on the Temperature module
       
    files = ['/sys/bus/w1/devices/28-011939e3f4d8/w1_slave', '/sys/bus/w1/devices/28-01204e866407/w1_slave']
       
    # A function that reads the sensors data
    def read_temp_raw():
        lines = []
        for path in files:
            f = open(path, 'r')
            lines.append(f.readlines())
            f.close()
        return lines
       
    def read_temp():
        lines = read_temp_raw()
        for i, line_set in enumerate(lines):
            while line_set[0].strip()[-3:] != 'YES':
                time.sleep(0.2)
                lines[i] = read_temp_raw()
       
        equal_pos = []
        for line_set in lines:
            equal_pos.append(line_set[1].find('t='))
       
        temps = []
        for i, pos in enumerate(equal_pos):
            if pos != -1:
                temp_string = lines[i][1][pos + 2:]
                temp_c = float(temp_string) / 1000.0
                temp_f = temp_c * 9.0 / 5.0 + 32.0
                temps.append(temp_f)
       
        return temps
       
    while True:
        t = read_temp()
        temps =  ",".join([str(round(x,2)) for x in t])
        print(f"{time.time()},{temps}", flush=True)
        time.sleep(30)
   

Note

This is part 1 of a project to create a PID controlled reptile heat mat. Buying a proportional thermostat that would accomplish the same thing would cost $60->$200. Far more expensive than spending 30 hours on it myself.