3

Smarter hot water

TUTORIAL

as required. Sensor 1 should be the one

at the top of the tank, and sensor 8 at

the bottom.

The box ‘Addressing the Temperature Sensors’

will show how you can find the code number for

each sensor.

PART 3

Opening the sensor drivers

Starts the 1-Wire interface.

PART 4

A subroutine to upload the data

to Google

This is the code that will write the data to your

Google Sheet. This is just a case of using the

update_sheet method from the pygsheets module.

The data is added into a new row near the top of

the sheet and the last row of data is deleted. Based

on repeating the script every five minutes, this will

capture 24 hours of data before being overwritten.

The first few rows are deliberately left blank to

leave space for a chart.

PART 5

A loop that runs eight times

• once per sensor
  This looping code is repeated eight times,
  once for each sensor. On each loop, it does
  the following:
  
  
  • Reads the sensor text file. This is made up of
    two lines of text.
  
  
  • Checks if the first line ends in ‘YES’ – if it
    does, then it knows the file has valid data.
  
  
  • In the second line, it looks for an equals sign
    and then saves the numbers that come after.
    This is the temperature data in 1000ths of a
    degree C.
  
  
  • The data is converted to degrees C.
  
  
  • If the temperature is above the threshold
    value, then it’s considered ‘hot’, and the
    variable hw_left is incremented by one. At
    the end of all eight loops, the total number of
    sensors above the hot water threshold value
    is converted to a percentage.
  
  
  • Based on the temperature, the colour of
    the corresponding LED is set: to fully red if
    above temp_max, fully blue if below temp_min,
    or an intermediate shade of purple for
    temperatures in-between.
  
  
  • Finally, the sensor address, temperature, and
    LED colours are printed to the screen. This is
    useful for troubleshooting.
  
  
  
  

PART 6

Formatting the data into a tidy state

The percentage of hot water remaining is calculated

and the time is converted to a useful format.

PART 7

Calling the data upload subroutine

The final step is a call-back to the subroutine

defined in Part 4. This writes the data to the

Google Sheet.

ADDRESSING THE

Every sensor has a 64-bit serial number that identifies it.

The digital data can be accessed through the Linux file

system at /sys/bus/w1/devices/<sensor address>. In this

folder is a text file called “w1_slave”. The temperature is

the last few digits, in 1000ths of a degree C.

TEMPERATURE SENSORS

Above

With the data

uploaded to a

spreadsheet, it’s

possible to make

charts of the

temperature over time