At CSSL (and other specialized snow monitoring stations) it's common to have a suite of instrumentation that measures the near-surface atmospheric conditions (i.e. standard meteorological variables such as air temperature, relative humidity, wind speed and direction) and a network that monitors the sub-surface, like soil moisture and heat flux. Sites instrumented with radiometers and eddy covariance allow us to quantify the radiation and turbulent energy exchanges between Earth's atmosphere and the ground/snow surface. What's commonly missing in this set up are sensors that help us quantify the energy exchanges happening within a snowpack due to the movement of water vapor caused by changes in vapor pressure and temperature gradients. 

Get a Temperature Reading

In order to use the 8-layer stackable HAT, you'll run through a series of steps to install a program that has many tools to read and configure the RTD sensors. You will work in your terminal and enter some command line text to set this up. Eventually you will run a small script to print the temperature and resistance values. 

Prerequisite - Enable I2C through the raspberry pi settings.

Now, working from the from the command line - 

Install RTD-RPI program (written by the Sequent Microsystems developers)

~$ git clone https://github.com/SequentMicrosystems/rtd-rpi.git

~$ cd rtd-rpi/

~/rtd-rpi$ sudo make install

Read about your different tooling options: 

~$ rtd -h

Run to program the channels for the pt1000 RTDs (default is pt100)

rtd 0 stypewr 1

Confirm this change by running

rtd 0 styperd

The result will be '1' which means the stackable HAT is programed for 1000 ohm RTDs

From here you can print each temperature sensor's temperature (below we'll do it in a more automated fashion). 

temperature(0,1) # Update, this is a place filler

The '0' here refers to the first 8-layer stackable HAT, and the '1' refers to the first temperature channel. Use (0,2) to get the second channel and so on. 

Let's now set up your python environment and get you ready to generate a script to read temperatures. 

For this project, I created a virtual environment to work in python. I named my virtual environment 'rpi'. 

python -m venv rpi

I then installed two python packages: ipython so that I could have an interactive python shell to test scrips, and SMrtd (Sequent Microsystems rtd package)

pip install ipython

pip install SMrtd

Here is my automated script to print the temperature, resistance, and a corrected temperature based on an ice bath calibration of 0 degrees C. Note, because I started to work with multiple sets of sensors, I have a separate .json file that holds the raspberry pi serial number and sensor offsets. 

import librtd

import json

def get_pi_serial():

    with open('/proc/cpuinfo', 'r') as f:

        for line in f:

            if line.startswith('Serial'):

                return line.strip().split(':')[1].strip()

    return "00000000"

# Load offsets from file

with open('sensor_offsets.json') as f:

    offsets_all = json.load(f)

# Get this Pi’s serial number

pi_serial = get_pi_serial()

# Get this Pi's specific offset dict

offsets = offsets_all.get(pi_serial)

if offsets is None:

    raise ValueError(f"No offsets found for Raspberry Pi with serial: {pi_serial}")

# offset_dict = {

#     1: 1.2,  # channel 1 offset

#     2: 1.3,  # channel 2 offset

#     3: 1.3,  # channel 3 offset

#     4: 1.2,  # channel 4 offset

#     5: 0.9,  # channel 5 offset

#     6: 1.2,  # channel 6 offset

#     7: 1.3,  # channel 7 offset

#     8: 1.3   # channel 8 offset

# }

# channel 1

t_ch1 = librtd.get(0, 1)

r_ch1 = librtd.getRes(0, 1)

c_ch1 = t_ch1-offsets.get('ch_1')

# channel 2

t_ch2 = librtd.get(0, 2)

r_ch2 = librtd.getRes(0, 2)

c_ch2 = t_ch2-offsets.get('ch_2')

# channel 3

t_ch3 = librtd.get(0, 3)

r_ch3 = librtd.getRes(0, 3)

c_ch3 = t_ch3-offsets.get('ch_3')

# channel 4

t_ch4 = librtd.get(0, 4)

r_ch4 = librtd.getRes(0, 4)

c_ch4 = t_ch4-offsets.get('ch_4')

# channel 5

t_ch5 = librtd.get(0, 5)

r_ch5 = librtd.getRes(0, 5)

c_ch5 = t_ch5-offsets.get('ch_5')

# channel 6

t_ch6 = librtd.get(0, 6)

r_ch6 = librtd.getRes(0, 6)

c_ch6 = t_ch6-offsets.get('ch_6')

# channel 7

t_ch7 = librtd.get(0, 7)

r_ch7 = librtd.getRes(0, 7)

c_ch7 = t_ch7-offsets.get('ch_7')

# channel 8

t_ch8 = librtd.get(0, 8)

r_ch8 = librtd.getRes(0, 8)

c_ch8 = t_ch8-offsets.get('ch_8')

# Print table header

print(f"{'Ch. #':<6}{'Temp (C)':<12}{'Resistance (ohms)':<12}{'Corr_Temp (C)':<12}")

# Print each channel's data

for i, (t, r, c) in enumerate([

    (t_ch1, r_ch1, c_ch1), (t_ch2, r_ch2, c_ch2), (t_ch3, r_ch3, c_ch3), (t_ch4, r_ch4, c_ch4),

    (t_ch5, r_ch5, c_ch5), (t_ch6, r_ch6, c_ch6), (t_ch7, r_ch7, c_ch7), (t_ch8, r_ch8, c_ch8)

], start=1):

    print(f"{i:<6}{t:<12.1f}{r:<12.0f}{c:<12.1f}")