Edge Collective

Satellite Modem Prototyping

Using a satellite modem to send data from off-grid.

Working with CPy 7 on Feather Blue Sense for now ...

Guide https://learn.adafruit.com/using-the-rockblock-iridium-modem?view=all#circuitpython-example

Rockblock Circuitpython library https://github.com/adafruit/Adafruit_CircuitPython_RockBlock

Library documentation https://docs.circuitpython.org/projects/rockblock/en/latest/api.html


Guide https://learn.adafruit.com/adafruit-esp32-s2-tft-feather/circuitpython

Adding an additional serial port to the Feather S2


Guide for maxbotic sensors: https://www.maxbotix.com/tutorials.htm

Sensor output options: https://www.maxbotix.com/tutorials2/sensor-output-options.htm

1-wire sensor

Guide to Circuitpython here

Using CPY 7.X on the Feather Bluefruit Sense for now

Message 75 and 76 are in the format:

data = struct.pack("f",batt_voltage)
data += struct.pack("f",depth_inches)
data += struct.pack("2f", sht.relative_humidity, sht.temperature)
data += struct.pack("2f", bmp.pressure, bmp.temperature)

E.g. Message 75:

IMEI: 300234065897350
Transmit Time: 2023-01-25T00:36:18Z UTC
Iridium Latitude: 42.4393
Iridium Longitude: -70.7191
Iridium CEP: 544.0
Iridium Session Status: 2
Data: 982f854090673f43bc35bb410028cf4188577d44646ccf41

Example python3 code for decoding:

>>> data=bytes.fromhex("982f854090673f43bc35bb410028cf4188577d44646ccf41")
>>> struct.unpack("<6f", data)
(4.162059783935547, 191.404541015625, 23.40123748779297, 25.89453125, 1013.36767578125, 25.92792510986328)

Initial version of satellite modem that sends depth and sensor data, waits 1 minute in between:


Looks as though it's 1 credit per message.

The highest rate is 0.145 British Pounds per credit for 100 credits (.099 BP per credit when buying 1000 credits).

So that's a purchase of $17.86 for 100 credits ($.18 per credits); or $121.94 for 1000 credits ($.12 per credit)

We might be able to pack more data in per message ... i.e., we could perhaps send several hours' worth of data once per day ...

But let's say we want to send one message per day. That's one credit per day.

So, 30 credits per month.

The line rental is $16 per month.

That's $5.40 per month for the messages, and $16 per month for the line rental -- so, that's about $22 per month

Decoding python structs using javascript



Better: a nodejs package python-struct: https://www.npmjs.com/package/python-struct

Or alternatively: https://github.com/lyngklip/structjs which seems to include easy to use source code ...

Using python-struct ...

Better link? https://stackoverflow.com/questions/5605108/pack-unpack-functions-for-node-js

Working code using structjs:

Gist: https://gist.github.com/dwblair/cc651bcb3bd11f13840c074c80bd924b

Structjs: https://github.com/lyngklip/structjs

Working repository (needed to make it a 'type':'module' ... ?): https://github.com/dwblair/js-python-struct-converter

Sending / relaying data on server / rock7 side

rockblock webhooks: https://docs.rockblock.rock7.com/docs/integration-with-application

Data compression for rockblock

Suggestions on compressing data for the rockblock https://docs.rockblock.rock7.com/docs/compressing-your-data

Adaptive retry for rockblock


Rockblock Credit System

Credits are used each time you transmit. 1 credit is used per 50 bytes (or part thereof) of message sent or received. 1 credit is also used if you check your mailbox and there are no messages waiting (A mailbox check). Credits do not expire unless you do not use your account at all for 12 months. Credits are shared/pooled between all of the devices on your account


Update Jan 31 2023

Rockblock is sending depth data, pulling readings from analog pin on the depth sensor. The Circuipython firmware is v 7.X, and is from here: https://github.com/dwblair/rockblock-ultrasonic/tree/main/firmware/v1

The rockblock sends it data to the rockblock server, which has a 'webhook' that sends an HTTP POST JSON of data to

The firmware on the rockblock encodes its data using a python struct approach

A 'relay server' is running at, using code from here: https://github.com/edgecollective/iridium-bayou-relay. The relay server decodes the data using a js version of the python struct approach, and then does an HTTP POST of the data to bayou.pvos.org at the '2ifhwi34ue4j' data feed