5 ms·

Reading this has reminded me of something I wanted to explore in the past. Most of my applications/requirements for a Pi include GSM, but I've found GSM modules

Reading this has reminded me of something I wanted to explore in the past. Most of my applications/requirements for a Pi include GSM, but I've found GSM modules to be very expensive, often being more expensive than the Pi itself. The author mentions a mobile USB modem, and it's just dawned on me that older 3G/HSDPA dongles are often very cheap. Does anyone have experience using them, especially what power implications they bring? They do bring a bit of bulkiness on the Pi, and are easy to steal, but then if one can access the modem, the whole Pi might be at risk too.

option_greek 7y ago
GSM isn't that costly: https://www.aliexpress.com/item/32827342779.html https://www.aliexpress.com/item/32827342779.html
- nevi-me 7y ago
  Thanks for the link. I haven't explored AliExpress as we have a cap on how many items we can buy before we're deemed to be "importers" for customs purposes. I'll take the plunge and apply to be an "importer", so I can start buying from there.
Jenda_ 7y ago
SIM800L costs $2. It supports GSM (AT commands - dialing, SMSs etc.) and GPRS (both PPP and a direct TCP connection to a hostname and port). Regarding USB dongles, I've been running Huawei E3131 with RPi. I needed to put +5V directly onto the pin header, but maybe now with the USB-C RPi4 the power should be stable out-of-the-box. I have heard rumors that the modem freezes after a while, but I've never ran it for longer than a few days. I'd recommend either investigating whether you can hard-reset the modem with software (cycling the USB power) or even putting a watchdog that will cut power to the entire RPi. Regarding power consumption, SIM800L is fine in idle, a few mA. However, USB dongles AFAIK do not support power save and they will eat ~100 mA all the time, which might be a significant portion of your power budget.
- nevi-me 7y ago
  Wow! Thanks, I saw SIM800L but thought that it's maybe some add-on, because the Pi/Arduino GSM components I normally see do cost more than a Pi 3. The prices that I'm seeing are an equivalent of US$10, but that's good enough. I'll buy one and try it out. I see it only supports GPRS though, are there other cheap devices that support faster connections like EDGE/3+G? If one wants to send things like images from a camera, a faster connection would be more reliable.
  - hutzlibu 7y ago
    With 3+G you will need more power.. and a faster connection would not be more reliable ... just faster. So if you want to have a real-time video-stream, than you need that. But for a security cam, gprs and low resolution images should be fine.
    - mentat 7y ago
      I believe the Narrowband stuff that Twilio's starting to roll out it's meant to address this.
- mdorazio 7y ago
  Keep in mind that most networks in the US are sunsetting GSM/GPRS within the next two years if they haven't already. Building anything dependent on this is a tricky proposition.
el_benhameen 7y ago
This isn't an answer to your question, but can you tell me more about how you source your sims/data plans?
- nevi-me 7y ago
  I haven't done anything practical yet, but in our country (South Africa), we've had a law recently that forces the cell network providers to allow consumers to transfer data around. For basic use (maybe 10 devices), I would be able to share my phone's data plan. I'm on a generous contract that gives me more data than I need (fiber at home). For larger volumes, most providers will either allow you to pool a number of SIM cards' usage into a single account, especially if you restrict them to only connect to a private network. We have this at my workplace on most SIM cards in laptops. There are also companies that supply SIMs to merchants and IoT folk on behalf of network providers. I'd also look into that. In most cases you end up with each SIM having its own data plan. I did some freelance work for one of these companies last year, if you have enough volume, you can negotiate pooling of data.
- teraflop 7y ago
  I investigated this a year or so ago for a hobby project. The best cheap option I found for non-trivial amounts of data in the US was T-Mobile's $10/month plan, which comes with 2GB/mo of high-speed data, and throttles down to roughly 64kbit/sec after that.
  - el_benhameen 7y ago
    I thought about something similar. T-Mobile based MVNOs have pretty good pricing, too, so maybe I'll do that.
  - tehlike 7y ago
    Project fi might be interesting too.
    - teraflop 7y ago
      Yeah, that would be an option. But IMO the biggest downside would be that they charge for overages instead of throttling. If I'm working on a hobby project that involves uploading data, and something gets into an unexpected state, it's easy to imagine it transferring tens of GB in a matter of hours. In that event, I'd rather have it restricted to dialup speed (which is still enough to transfer 20GB/month) than get hit with hundreds of dollars in bandwidth charges overnight.
konstruktors 7y ago
Author of the blog post here. I've used [this SIM800 Raspberry Pi hat](https://www.itead.cc/wiki/RPI_SIM800_GSM/GPRS_ADD-ON_V2.0 https://www.itead.cc/wiki/RPI_SIM800_GSM/GPRS_ADD-ON_V2.0) and it requires some additional GPIO toggling to enable the modem after a power loss. [Here are the scripts](https://github.com/kasparsd/remote-pine https://github.com/kasparsd/remote-pine) for doing that and creating the PPP network interface. The USB modems are nice because you get full control over the modem with the AT commands. I've used the Huawei E173 modem which can be easily unlocked and works great out of the box.

option_greek 7y ago

GSM isn't that costly: https://www.aliexpress.com/item/32827342779.html https://www.aliexpress.com/item/32827342779.html

nevi-me 7y ago
Thanks for the link. I haven't explored AliExpress as we have a cap on how many items we can buy before we're deemed to be "importers" for customs purposes. I'll take the plunge and apply to be an "importer", so I can start buying from there.

Jenda_ 7y ago

SIM800L costs $2. It supports GSM (AT commands - dialing, SMSs etc.) and GPRS (both PPP and a direct TCP connection to a hostname and port). Regarding USB dongles, I've been running Huawei E3131 with RPi. I needed to put +5V directly onto the pin header, but maybe now with the USB-C RPi4 the power should be stable out-of-the-box. I have heard rumors that the modem freezes after a while, but I've never ran it for longer than a few days. I'd recommend either investigating whether you can hard-reset the modem with software (cycling the USB power) or even putting a watchdog that will cut power to the entire RPi. Regarding power consumption, SIM800L is fine in idle, a few mA. However, USB dongles AFAIK do not support power save and they will eat ~100 mA all the time, which might be a significant portion of your power budget.

nevi-me 7y ago
Wow! Thanks, I saw SIM800L but thought that it's maybe some add-on, because the Pi/Arduino GSM components I normally see do cost more than a Pi 3. The prices that I'm seeing are an equivalent of US$10, but that's good enough. I'll buy one and try it out. I see it only supports GPRS though, are there other cheap devices that support faster connections like EDGE/3+G? If one wants to send things like images from a camera, a faster connection would be more reliable.
- hutzlibu 7y ago
  With 3+G you will need more power.. and a faster connection would not be more reliable ... just faster. So if you want to have a real-time video-stream, than you need that. But for a security cam, gprs and low resolution images should be fine.
  - mentat 7y ago
    I believe the Narrowband stuff that Twilio's starting to roll out it's meant to address this.
mdorazio 7y ago
Keep in mind that most networks in the US are sunsetting GSM/GPRS within the next two years if they haven't already. Building anything dependent on this is a tricky proposition.

el_benhameen 7y ago

This isn't an answer to your question, but can you tell me more about how you source your sims/data plans?

nevi-me 7y ago
I haven't done anything practical yet, but in our country (South Africa), we've had a law recently that forces the cell network providers to allow consumers to transfer data around. For basic use (maybe 10 devices), I would be able to share my phone's data plan. I'm on a generous contract that gives me more data than I need (fiber at home). For larger volumes, most providers will either allow you to pool a number of SIM cards' usage into a single account, especially if you restrict them to only connect to a private network. We have this at my workplace on most SIM cards in laptops. There are also companies that supply SIMs to merchants and IoT folk on behalf of network providers. I'd also look into that. In most cases you end up with each SIM having its own data plan. I did some freelance work for one of these companies last year, if you have enough volume, you can negotiate pooling of data.
teraflop 7y ago
I investigated this a year or so ago for a hobby project. The best cheap option I found for non-trivial amounts of data in the US was T-Mobile's $10/month plan, which comes with 2GB/mo of high-speed data, and throttles down to roughly 64kbit/sec after that.
- el_benhameen 7y ago
  I thought about something similar. T-Mobile based MVNOs have pretty good pricing, too, so maybe I'll do that.
- tehlike 7y ago
  Project fi might be interesting too.
  - teraflop 7y ago
    Yeah, that would be an option. But IMO the biggest downside would be that they charge for overages instead of throttling. If I'm working on a hobby project that involves uploading data, and something gets into an unexpected state, it's easy to imagine it transferring tens of GB in a matter of hours. In that event, I'd rather have it restricted to dialup speed (which is still enough to transfer 20GB/month) than get hit with hundreds of dollars in bandwidth charges overnight.

konstruktors 7y ago

Author of the blog post here. I've used [this SIM800 Raspberry Pi hat](https://www.itead.cc/wiki/RPI_SIM800_GSM/GPRS_ADD-ON_V2.0 https://www.itead.cc/wiki/RPI_SIM800_GSM/GPRS_ADD-ON_V2.0) and it requires some additional GPIO toggling to enable the modem after a power loss. [Here are the scripts](https://github.com/kasparsd/remote-pine https://github.com/kasparsd/remote-pine) for doing that and creating the PPP network interface. The USB modems are nice because you get full control over the modem with the AT commands. I've used the Huawei E173 modem which can be easily unlocked and works great out of the box.