Liquid level meter with integrated GSM modem

This friendly support question liquid level meter with an integrated GSM modem reached me today

“I am not sure if this is the appropriate way to ask a technical question or if you have the time to answer this kind of questions atall, but I am desperate so I will just try.

I purchased a liquid level meter with an integrated GSM modem. As far as I know this is a 2G technology modem. Unfortunately I have not been able to get it to work. My guess is there is some sort of compatibility problem with the 3.5G sim cards (the only ones available here in Chile). Have you ever had similar problems? Can you point me in the right direction to look for a solution?”

I have seen trouble based on SIM cards before. The GSM modem you mentined is not state of the art. Anyhow, my first proposal is to put the SIM card in a older 2G mobile phone and to test it again.You mentioned not the cellular operator you try to use.

List of all cellular operators in Chile

Bad operators for you, because they support 3G only

  • Telefonica Movil de Chile (TELEFONICA) = 3G 850
  • Entel PCS Telecomunicaciones S.A. (ENTEL PCS) = 3G 1900
  • Nextel S.A. (Nextel Chile) = 3G 1700/2100
  • VTR MOVIL, S.A. (VTR MOVIL) =3G 1700/2100

Good operators you you, because they support 2G

  • Entel PCS Telecomunicaciones S.A. (ENTEL PCS) = GSM 1900
  • Telefonica Movil de Chile (TELEFONICA) = GSM 850/1900

The better option is to have a look on the GSM modem with embedded watchdog listed as below:

Some benefits of this GSM modem

  • Latest GSM Quad band modem technology inside
  • Hardware watch dog inside
  • Battery and charger inside
  • Option to run own code on Python inside

GSM modem application examples

Burglar alarm, monitoring of server room, standard AT modem with watchdog, operating hour timer of machines, remote control, remote monitoring, fault detector, data logger … and a lot of more. Liquid level we can measure and detect as well.

If you have interest in this GSM modem made by a business friend of mine then just drop an email to harald.naumann (at) or use the form to get further details.

Updated: 2011-12-21 — 3:55 PM


Add a Comment
  1. Hi Harald,

    I appreciate you taking the time to respond.

    Unfortunately I do not have the luxury of replacing the modem because it is part of the level meter, but I will try to get an old 2G phone to try the SIM card as per your suggestion above.

    I have been trying mostly with Entel. From your list above, Entel operates both a 3G and a GSM networks. Whatever the modem is, I suppose the SIM card determines to what network the modem will try to connect. If that is the case, I understand I am trying to connect to Entel’s 3G network with a modem that does not support the technology. Is there a way to force a connection to the GSM network?

    If you or your business partner have or can recommend a robust lever meter (the one I am using is ultrasound based) with an integrated GSM modem, I would be more then happy to consider replacing the one I have. I expect to buy quite a few of those in the future.


  2. Hi Christof,
    It was a pleasure for me to support you. We are close to Christmas and at Christmas everybody make presents. Me too. 🙂
    Your trouble with SIM cards was common for me. Something with 3G SIM cards is different and then the SIM cards will not work with older 2 G GSM modem. The network of ENTEL is supporting 2G and 3G. Where is a 3G tower there is a normally 2G tower as well. In Germany we still have regions with 2G coverage only – no 3G coverage. If an operator has a 2G and 3G licence then 3G only coverage only I never have seen. This makes technical so sense. 2G is a much older technology. There are still people that own 2G phones only.
    One of my customers is high skilled in liquid level measurement. The link to the GPRS modem with watch dog has an I2C bus and a RS232. On both serial links my business partner can wire any kind of sensors. Last, but not least a customisation is possible. This makes sense, if the quantity fits to the costs for redesign.
    Most of the bigger accounts get a customised version. They ship a standard version with some changes, the customer is testing it and after they place an order for redesign.
    My daily job is Field Application Engineer Wireless for a big European distributor. From time to time people ask me for developing of wireless applications. I am not able to do that. There is to less time left. I spend a lot of time with reading and learning. I also make at least one article per week in average public. This week it was already four. I just started to answer questions online. This saves time, because if next email or phone call comes in with same question, then I just will send a link.

    Before it is forgotten: A Merry Christmas to everybody that will read this article.
    Best regards from North of Germany
    Harald – waiting for Santa Claus

  3. Hi Harald,

    it works!!!! The problem was not with the modem but, as too often, with the user. The level meter works in two modes: SMS and GPRS. Since setting up SMS mode is a lot easier, i tried that first, but without confirming that the SIM card allowed sending SMS messages. Guess what! It didn’t! Then tried to use GPRS mode that requires setting the APN and a few other parameters. In short, I got one of the parameters wrong and since the device does not provide very meaningful or detailed error messages… A very basic mistake. Please excuse me for taking your time.
    Despite of this success, I am still very interested in checking out other options. To begin with, I will have a look the GPRS modem with watchdog you mentioned above. In addition, I would be interested in an off the shelf GPRS device with industrial analog and digital inputs and outputs.

    Thanks again!

    Frohe Weihnachten und ein schönes neues Jahr,

  4. Hi Christof,
    I it most time a user mistake. The SMSC number for SMS is most time stored on the SIM card. If you use GPRS then on a mobile phone delivered by operator everything is installed. If you order a non branded Samsung S2 like my friends, then you get the APN automaticly by download.
    GSM modems are stupid. Stupid and often much more robust than a smart phone.
    BTW, The watch dog is the key. If the device will ever hang, the watch dog will will make a power down resest.
    Just send an email. I will help with an answer.

    Auch Dir frohe Weihnachten und ein gutes, erfolgreiches Jahr 2012. Ich habe seit wenigen Stunden Urlaub und freue mich auch ein paar die nächsten Tage.

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