Excessive consumption data Raspberry Pi USB Modem


Hi everyone, I’ve been developing a IoT monitor and sending the data to ThingSpeak.com. The application is monitoring off grid micro Wind Turbines in rural Peruvian communities.

I’m using an Arduino Uno as a sensor interface, and then that’s connected to a Raspberry Pi 3 with a USB modem. I had previously been using big name chips, but we were paying between $7 and $10 a month as we were using standard packages from the likes of Claro and Bitel (two big networks here in Peru). I saw the Hologram as a way of reducing our data spend, but I’ve had a bit of a shock…

Using Node Red, I’ve got 10 minute average data being sent to 8 channels on ThingSpeak, in addition I have 2 hourly figures (generated and consumed power). Honestly I’m not sure how much data that actually is, but a string of float numbers can’t require that much data can it?

I’ve trialed the device with an Hologram SIM, and the data usage seems rather erattic.

I can see the regular 10 minute transmission between 11kb and 32kb, but then have these random ones of a few meg?

Could the Pi be downloading a minor update? I was under the impression those are sudo commands?

I’d appreciate any comments on this, as I’m rather puzzled;
a) does 11kb - 32kb seem about correct for 10 channels of data?
b) will the Pi do minor uploads.

At the start I topped up with $5 thinking that would be fine for the month, but at this rate, it’ll be cheaper to go back to the standard Peruvain SIMS.

Thanks for helping a comms newbie out!


Hi @windaid - Thanks for reaching out. What type of USB modem are you using and how is it configured for internet access with the Pi? Responses below based on your questions.
a) does 11kb - 32kb seem about corrent for 10 channels of data
The data usage for each cellular session includes all traffic passed over the internet from the Pi including headers so depending on how the data transmissions are passed from your Node Red application >11kb to send a payload of a float number value is possible. A lighter-weight method of sending data via our Python SDK is an included benefit when transmitting over cellular where every byte counts.
b) will the Pi do minor uploads
When connecting the Pi over USB modem, unless configuration and network routing is controllable all internet traffic in addition to your application’s data will be transmitted over cellular. If you have any other applications running updates or syncing data that could be causing the intermittent 1MB data usage sessions. Here’s an example of Debian Unattended upgrades.

Let us know if you have any other questions, hope this helps.