Originally published at: https://contextualelectronics.com/topic/eg91-bg95/
In this video we go over the reasoning behind the chosen bluetooth chip and some of the basics functions we’ll be utilizing on board the BLE-CELL platform. Block diagram for BLE-CELL EG91 Product Page BG95 Product Page Cat 1 vs Cat M1 Hologram Introduction to AT commands Some of the topics covered: Why cellular? What…
Hrm, a bit of audio delay, I think from plugging in my microscope to the computer (additional video processing). Will see if I can update the setup and edit this video.
Interesting! It looks as though those modules support PPP, which might be a good option to start with. It makes it possible to do “normal network stuff” both from the Raspberry Pi (a PPP connection over a serial port looks like just another network connection in Linux) and from the nRF52840 (mbed has support for PPP too: https://os.mbed.com/docs/mbed-os/v5.15/reference/cellular-networking.html). Those cell modules do have application level AT commands (HTTP, MQTT, etc.), but it feels more natural to me to have that sort of application-level stuff in your application code on the MCU. The built-in AT commands might be more energy efficient than using PPP, but they’d probably mean writing more (and trickier) code on the MCU.
I think this is going to be quite an entertaining series!
Thanks for doing this series, Chris. It’s been very helpful as well as timely for me, as I’m looking to build a project around a cellular module soon, also with an nrf52.
One question, though:
I can’t seem to find anywhere to actually buy EG91/BG95s. At least none of the usual suspects, nor octopart have orderable parts. I’ve found a few sketchy options, with fairly high prices…
I was also considering the nRF9160, and I can find that everywhere, for ~19-20 or about half of the best price I could find the Quectel options. It looks like it would be a great combo part for one of the cheaper nrf52 parts too, and since it is also from Nordic, you’d be able to use the same SDK with both chips.
Did you consider the nRF9160 and decide against it for cost or other reason(s)? Is the Quectel part available for less somewhere that I don’t know about?
As far as I know, the only way to get the Quectel parts is direct. I reached out to them and talked to a sales rep, who put me in contact with the factory. I paid $15/part for prototype quantities (plus shipping from China), and production will be less than $10 per module.
The nRF91 is a lovely chip but is not targeted at folks using them as modems. There were some downsides that I had heard from folks, but didn’t substantiate, the main one being that they were not qualified on networks in the US outside of Verizon. Even then, they were struggling to get certified, though I believe they have gotten through.
Another thing I didn’t look at, but might have been FUD on my part, was that there isn’t a “default” firmware image. I believe the nRF91 requires an image on there using Zephyr, but I honestly didn’t look into it too much.
The other big reason is that the BG95/EG91 allows switching to non-Cat M1. This is really me hedging my bets for any areas that might not have Cat M1, as I experienced it on a previous gig I was working on. There are unfortunate realities about where the devices will be deployed that cannot be swapped after the hardware is made. In response, I made it so the device can be used for either Cat 1 (EG91) or Cat M1 (BG95), with the former being about double the price.
If you find more reasons to use the nRF91, I would love to hear them! Cellular coverage is a weird market, and I’d love to gain more knowledge around it. I can also refer you to some folks who work on the data side, namely my former colleagues at Hologram.
Thanks for all the detail, Chris!
It looks like they do have a fully implemented default firmware now. Here is the documentation for it: https://infocenter.nordicsemi.com/pdf/nrf91_at_commands_v1.3.pdf
As far as network support, I’ve read in the Nordic forum of success with Twilio’s super-sim, which uses T-mobile in the US from what I understand. Dunno too much about this, though and don’t yet have firsthand experience. I picked up a DK for cheap from an ebay recycler, and will be playing with it soon.
Also, Jared Wolff’s Feather DK (https://groupgets.com/campaigns/814-nrf9160-feather) comes with a Hologram supersim hyper sim. (What’s with these product names? 
) He’s documenting his experience developing the board on his blog, and it is a great read.
Yeah, I have enjoyed reading Jared’s experience. I had put him in touch with Hologram, I was glad they are sampling their SIM with his board.