Team StellarNet:

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Published January 22, 2018

StellarNet Real-Time Cellular-Wireless Spectrometer

We are sending commands and receiving real-time UV-Vis-NIR spectroscopic data from a linear pixel array spectrometer over Cellular-WiFi

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StellarNet Real-Time Cellular-Wireless Spectrometer

Things used in this project

Hardware components

StellarNet BLUE-Wave-Vis

Raspberry Pi Zero Wireless

Hologram Nova

Story

Our team makes small, research-grade spectrometers with a focus on rugged design.

These instruments have no moving parts and are very popular for remote applications and extreme environments (we have a couple of projects on the International Space Station).

Many of our customers want to be able to operate their instruments remotely. They might set up a project to monitor plankton from a research buoy; measure solar irradiance from a weather balloon; set up research stations in the Amazon to measure the light transmission of rainforest canopy at different times of year; conduct snow reflectance measurements in Alaska; applications are endless.

One of our colleagues, Scott Jordan, wrote a fantastic bit of code to send JSON interface commands and receive X,Y spectral data as long as the spectrometer is connected to an internet connected computer. Using this code, we can theoretically conduct research from anywhere around the world.

We were very excited when we saw the Nova and what it could do because it opens up new (affordable) possibilities for sending and receiving data to our instruments.

My colleague, Sebastian Gondor, wired up the project and tested the code. Seba made modifications to our code to accommodate for the Nova's eccentricities.

We nearly didn't publish this because our instrument outputs 2048 data points which is too large for the nova to do real-time communication with. Originally, we could only send very small amounts of data and a user on the community showed us how to expand the data limit a little. We ended up interlacing the data and cutting out every other pixel to give a full spectrum. We thought about packeting the data but it was too complicated and would slow down the system.

Overall, from a viewpoint of "proof of concept," the project is a huge success!

The existing setup and code can be used to conduct research from a distance without having to collect time-series data and physically retrieve the instrument.

Accessing Raspberry Pi Zero W without a monitor

If you don't have a monitor and a keyboard to access your Raspberry Pi Zero W like us, don't panic! There is a cool way to access it without anything of that, you just need the following materials:

Raspberry Pi Zero W

Micro SD card

Raspbian Stretch Lite (in our case)

Etcher to mount OS image

Putty for SSH access

And then is as simple as following this tutorial.

Which steps are basically these:

Download Raspbian OS

Flash the Micro SD card with the OS using Etcher

Enable SSH by adding an empty file called “ssh”

Enable auto-connect to your wifi by adding the file “wpa_supplicant.conf” with your wifi configuration

Done! Now you can use Putty to access your Raspberry Pi Zero W remotely! Isn't that cool!?

Install Hologram Nova Python SDK

Now that you have access to your Raspbian OS (it means that you already have internet access!) then you can install Nova tools following this tutorial.

Materials:

Raspberry Pi Zero W

Hologram Nova with SIM card activated

It only takes two lines to install Hologram Nova python drivers and now you are ready to send/receive data to/from the dashboard!

Send from Raspberry

Receive in Dashboard

Install StellarNet drivers

Due to copyrights we are not able to publish the drivers to control Stellarnet products, but basically you only need to install pyusb 1.0.0a3 and copy the drivers to Raspbian OS.

Hardware

USB Charger

USB Hub

USB Adapter

Raspberry Pi Zero W

NOVA Hologram

StellarNet Spectrometer

Hardware

Firmware

Import libraries and create Hologram object

"Send message" function

We also created this function to check incoming SMS so we can now configure the Spectrometer remotely and also ask for information!

Processing incoming SMS

In the main loop it will send the spectrum every 30 minutes (by default) or every pull time configured, and also check incoming SMS.

Main loop

Results

Sending a spectrum

As soon as we run the python script it send the first spectrum, and then will do it every "pull time"

Message sent!

How it looks in the dashboard (super long message!)

Processing SMS

Now let's try to talk with the spectrometer using SMS...

SMS to ask for configuration info

We have a new message!

Here comes the message!

And here is the answer:

Config. message in the dashboard

############################################################

This is the end of the post and we want to thank you for reaching the end!

Now the sky is the limit!

Thanks!

StellarNet team

StellarNet and Hologram Nova

import stellarnet
import time
import datetime
import json

from Hologram.HologramCloud import HologramCloud

# Hologram cloud object
hologram = HologramCloud(dict(), network='cellular')

pull_time = 1800    #Pull time. Every 30 minutes
device_id = '0001'  #Default ID name

#############################################
# Spectrometer object
#############################################
class Spectrometers(object):
    _map = None

    def _get_map(self):
        global _map

        if not Spectrometers._map:
            Spectrometers._map = {d.get_device_id():{'device':d,'config_id':0} \
                                      for d in stellarnet.find_devices()}
            
        return Spectrometers._map

    def __getitem__(self, device_id):
        try:
            return self._get_map()[device_id]
        except KeyError:
            abort(404)

    def get_device_ids(self):
        return self._get_map().keys()

spectrometers = Spectrometers()


#############################################
# Set configuration
#############################################
def handle_config(_device_id, parameters):
    spectro = spectrometers[_device_id]
    device = spectro['device']
    device.set_config(**parameters)

#############################################
# Get connected spectrometers
#############################################
def get_spectrometers():
    device_ids = spectrometers.get_device_ids()
    return json.dumps({'device_ids':device_ids, 
                    'timestamp':int(time.time()*1000)})

#############################################
# Get spectrum
#############################################
def get_spectro(_device_id):
    spectrometer = spectrometers[_device_id]
    spectrum = spectrometer['device'].read_spectrum()
    return json.dumps({'data':spectrum[0:1700], 
                    'timestamp':int(time.time()*1000),
                    'config_id':spectrometer['config_id']})

#############################################
# Get spectrometer configuration
#############################################
def get_config(_device_id):
    spectrometer = spectrometers[_device_id]
    config = spectrometer['device'].get_config()
    return json.dumps({'config':config, 
                    'timestamp':int(time.time()*1000),
                    'config_id':spectrometer['config_id']})

#############################################
# Send main function
#############################################
def send_message(_message, _topic, _timeout):
    # Connect to the cloud
    print (datetime.datetime.now())
    connection_status = hologram.network.getConnectionStatus()
    print ("Connection status: {}".format(connection_status))

    if (connection_status == 0):
        # Only connects if not connected yet
    	connect_status = hologram.network.connect()
    	if(connect_status == False):
    		print ("Connection failed")
    		return
    	else:
    		print ("Connected to network")

    # Send message
    response_code = hologram.sendMessage(_message, topics=_topic, timeout=_timeout)
    # Log send status
    print ("Send result: {}".format(hologram.getResultString(response_code)))

#############################################
# Send spectrum to the cloud
#############################################
def send_spectrum():
    # Get the spectrum
    spectrum_message = get_spectro(device_id)
    print ("Sending spectrum of size: {}".format(len(spectrum_message)))
    # Send message
    send_message(spectrum_message, "spectrum", 20000)

#############################################
# Send configuration to the cloud
#############################################
def send_config():
    # Get config
    config = get_config(device_id)
    print ("Sending config message of size: {}".format(len(config)))
    # Send message
    send_message(config, "config", 500)

#############################################
# Send spectrometers list to the cloud
#############################################
def send_spectrometers():
    #Get spectrometers
    spectrometers = get_spectrometers()
    print ("Sending spectrometers message of size: {}".format(len(spectrometers)))
    # Send message
    send_message(spectrometers, "spectrometers", 500)
		
#############################################
# Process incoming sms
#############################################
def check_sms():
    global pull_time
    global device_id
    sms_obj = hologram.popReceivedSMS()
    print (datetime.datetime.now())
    if sms_obj is not None:
        print("SMS: New message:{}".format(sms_obj.message))

        command, value = sms_obj.message.split("=")
        if command == "DEV_ID":
            device_id = value
            print("SMS: New dev ID:{}".format(device_id))
        elif command == "PULL_TIME":
            value_int = int(value)
            if value_int > 0 and value_int < 600:
                pull_time = value_int
                print("SMS: New pull time:{}".format(pull_time))
            else:
                print("SMS: Wrong parameter. Pull time:{}".format(pull_time))
        elif command == "GET_SPECTRUM":
            send_spectrum()
        elif command == "GET_CONFIG":
            send_config()
        elif command == "SET_CONFIG":
            print("Set Config: {}".format(value))
            handle_config(device_id, value)
        else:
            print("SMS: Wrong command")
    else:
        print("SMS: No messages")


#############################################
# Main loop
#############################################
while True:
    send_spectrum()
    check_sms()
    time.sleep(pull_time)