ComGSM update – success at last!

I have now succeeded in getting my ComGSM substitute to work. I’m grateful for the suggestions and advice I’ve received.

I have come to the conclusion that the TC35 board I originally bought just won’t work in this situation. I can’t really come up with a good reason for why, but as described in previous posts it doesn’t function correctly when connected to the panel. I think it does now work though so maybe I’ll find a use for it in another project.

I have now connected up the SIM800L module along with the voltage regulator and it worked perfectly first time. It is clear that this is a much more up-to-date module, being a fraction of the size of the TC35 one. It also uses a micro-SIM rather than a full size one which is handy. It is possible to insert the SIM the wrong way round though, which caused me some consternation until I realised it.

After some rough testing I’ve now permanently installed the two boards inside the metal casing, with the antenna fixed to the outside. I’m very pleased with the end result which is very ‘stealthy’ and actually to my mind is much neater than the official Texecom unit.



Here is the whole cabinet, with the SIM800 module next to the main board on the right and the regular board hidden behind the bundle of sensor cables (note the incredibly bright green LED!). The antenna is on the top with the black cable just about visible.

These show the detail of the antenna, regulator and SIM800 board.

I then configured the panel with COM1 as the GSM module, and much to my relief after restarting the panel saw this in the ‘Online Status and Control’ window in Wintex:


The bottom right shows that GSM signal strength and bit error rate as both being normal. The ‘online’ doesn’t mean anything as it says this even when nothing is connected.

As usual there is a huge amount of configuration you can do, and this is contained in the manual for the real GSM unit. It is wise to tone down the notifications, since as default you will get an SMS message every time the panel is armed or disarmed and it seems to store a backlog. When I first got it working I got loads and loads of text messages for the last week or so.

I need to properly test that it will send me a text if the alarm goes off but I’m sure it will work. You can also send various commands using SMS, but the issue I have with this is that you need to prefix them all with your code which means that if anyone got your phone they could easily read it out. However this is in reality rather unlikely.

I use giffgaff for the mobile phone service, mostly because I use them for all the other phones in our house as well. I’ve found them to be very good and I’d definitely recommend them.

So I am happy that finally this project is completed and at very little cost. I’ve developed the capability of the alarm and it does now stand alone in the event of a power failure etc and can get to the outside world without relying on the Internet.

So… what’s next? Well, I am getting interested again in intelligent heating control systems and have recently ordered some new bits, so will post about this when I have some time. In the mean time, if this interests you I’d thoroughly recommend Andy Carter’s blog on the subject which I’ve found a mine of useful information.

51 thoughts on “ComGSM update – success at last!”

  1. Sorry for the late response.. recently i’ve been looking into adding a comip to my dinosaur texecom 88 panel .. and google led me to your page ! i’ve been running a texecom 88 system for several years now with my home build gsmcom based on a siemens mc35 terminal module. After some research (of pinouts and command set) i figured i would try to get it to work . After finding the right pinout on the panel all it required was a max232 level convertor and a voltage regulator to get it to work like a charm!

    I would like to thank you for your research on the ipcom solution, i was gonna go for a comwifi because that module is much cheaper, but nothing beats your solution (got like 3 pi’s lying around still 🙂 so wired ethernet it will be)

  2. Great, glad it’s helped. The comwifi is definitely better on price that the comip but has some issues, not least how the antenna is dealt with. Good use for a spare pi!

  3. Hello,
    I’ve bought the SIM800L and a regulator. In photos, it’s difficult to see wires from the SIM800L and the texecom panel. I supposed there are only 3 wires, one for TX, one for RX and the last for GND. Am I right ? Finally, have you swapped TX/RX ?
    Thank you

  4. Yes that’s right, there are just those three wires. The power to the board is on a separate terminal block on the board. I have swapped TX/RX over, so TX on the SIM800 goes to RX on the board and vice versa. However all of these modules are slightly different so if you hit problems it is worth trying them the other way round before doing anything else.

  5. Yes, I figured out why some modules/firmwares work and others don’t…
    It is all about the echo, echo, echo!
    The only “right” answer (for this system) does not start with an echo (instruction repetition) nor with an empty line CR LF. The command ATE0&W eliminates the echo for my SIM900A, but does not kill the leading CR LF…

  6. Test done with succes!
    Smashed a oversized ATMEGA in between the GSM-module respond line.
    Filtered out the “empty” CR LF lines: now all runs fine.
    Except the AT+ command where the system wants to know if the TAMPER? status is OK.
    The classic, understandable respons. in this ‘unknown’ case is just “ERROR”.
    WIP: replaced the Atmega by his smaller brother, a ATTINY85

  7. Wow, great work! Looks like I was lucky with the module I got. This does explain why the first one I had didn’t work. Luckily for me the second one did and was cheap. I wonder why these variations occur?

  8. The AT instruction set is common, the responses are slightly different/equal but strong alike.
    Each firmware (hardware dependent) has it’s own respons flavour. To co-operate, there needs to be a match, made in heaven… or by tweaking humans.

  9. Hi,
    Also tried to fit a SIM800 module as shown on the picture above but can’t get it to work.
    End up with a com 1 fault.
    Anyone would like to share how to activate? I use the wintex software.
    I find it a bit confusing in the soft as there are several tabs were you can specify com ports on each tab. Might be a noob question 🙂

    Can’t you alter the AT settings by using the ATS3 / 4 / 5 options?
    These control the terminating and other characters. Might save you the hassle of using an intermediate device (attiny85).

  10. Hmm OK – have you tried connecting to the board directly just to check that it’s working? The place to configure it is in the ‘Panel Com Port Options’ tab in the ‘Communication Options’ menu. You need to set ‘Com Port 1’ to ‘GSM Module’ – assuming you have connected it to the correct header on the board.

    It does appear that there is more variation in these boards that I originally thought but a few people have got SIM800 modules working, so it’s worth persevering. Also check all the simple things like wiring, order of pins etc. Also worth swapping over the TX / RX lines just in case your module has them wired the wrong way round.

  11. Hi,
    Indeed I first hooked up the module to my pc via a USB to serial and is just working fine.
    It responds to the AT commands I tested.
    I’ll have another look to the settings in the wintex software.
    Thank you for your comment and tips!

  12. Jan:
    The first CR LF line is -firmware- intended to be there, the alarm firmware does not like that and rejects the further respons. Blew my Sim900A module (while testing and soldering), ordered a Sim800 module that arrives in a few days… We will see how plug-and-play that will be.

  13. Sim800L (eud.dx) received, but not working with the system…
    Few minors on this version: unit is not 3V3 nor 5V but 3.7V – 4.2V.
    UART lines or not 5V tolerant, level shifter needed.
    The Sim800L EVB type counters all these issues!
    Even with all hardware the adpations, the init sequence does not get out of loop.
    Still believe the secret to success is hidden in the firmware version.
    Mine respons to AT+CGMR with:1418B02SIM800L24
    What do you guys get from yours working type?

  14. I have a SIM800L module with exactly the same firmware 1418B02SIM800L24 (hence me arriving here via Google!) and am trying to connect to the O2 / GiffGaff network, but it refuses to register to it.

    All the AT commands are accepted and responded to correctly over the serial link. Doing a command AT+COPS=? correctly lists all networks in my area, (2,”O2″,”O2-UK”,”23410″), being one and the signal quality is AT+CSQ 16,0

    I’m using an Arduino MEGA 2560 to talk to it and powering off its 5V output through a signal diode to drop it down to 4.2V for the SIM800L. I’ve also powered it separately off a laboratory bench DC supply. No difference. The red LED flashes once a second.

    I’ve been told you have to get a 2G SIM, so I got one of those 2G SIMs off eBay advertised as “working with GPS trackers” but that didn’t work either.

    What’s the big secret to getting the SIM800L module to register on a UK PAYG network? Any help would be very gratefully received! Thanks in advance.

  15. Interesting… looks like it is quite hit and miss with these modules after all. I can’t easily interrogate mine at the moment, but I’ll do so next time I open the box and report back. However it might be simpler to buy another module from a different manufacturer and try that one. I can imagine that there might be differences in board design or implementation which are tripping things up.

  16. I’m using a GiffGaff SIM which does have a 2G network available. When you start up you should see a slowly flashing LED, then there should be a pause, then a rapidly flashing LED which indicates that it has registered. The slow flash you are getting is consistent with it not registering. What you do need to do is get the SIM in a phone first, and then get some credit on it before putting it in the module. I don’t think that they set up correctly if you are putting it in the module brand new. You usually get a few text messages etc as the network intialises it. I had problems until I did all this on the phone, and then put it in the module. Have you tried this? Can you try another SIM (eg from your normal phone) and see if it behaves differently? It might just be a duff module, I am not sure how good the QC is and before tearing your hair out too much it might be worth trying another one. Could you let me know how you get on?

  17. Many thanks for the replies. I had already done all you suggest and was indeed at my wit’s end.

    Further experiments and another speculative purchase from a UK dealer resulted in a working module.

    I suspect the original I bought from China was actually tied to China networks (but how?) All it would do was respond to all the AT commands, scan networks, but refuse to connect to O2, Orange, Vodafone, Three or T-Mobile.

    The UK supplied module, even though it had the same firmware, works perfectly and connects after only a few seconds following power-on. Even with the little pigtail antenna it came with for me to solder on.

    I note that the faulty / China-tied original had a red LED whilst the one I got from a UK supplier has a green LED. Otherwise, the SIM800L Coreboards, as they are called, are identical. A clue maybe?

    Another observation is that while the SMS function is easy to use and trouble-free, the HTTP GET functionality through GPRS is very tricky! I HAVE got it to work but it’s a bit hit and miss. Probably because it really should be connected to a 3.7V LiPo rather than my current experiment setup, which is a 9V battery into a 7805 regulator and then through a diode to drop the voltage! (Which is still a little high at 4.3V, but two diodes in series makes the voltage too low!)

    Incidentally, I have tried a laboratory DC supply too, but haven’t done the HTTP GET attempts using that yet. It’s taken me a couple of weeks to get to THIS stage!

  18. Great, glad you got it working in the end. I suspect the problem was nothing more than a faulty module, I doubt they are so sophisticated as to lock them down in this way! I’ve not tried using GPRS with them as yet. Would be interested to hear how you get on

  19. I had a SIM800L EVB v2.2 module which came with a pair of red LED’s on it. Initially this failed to connect to the network on giffgaff when testing on the bench. This turned out to be for the following reasons:
    1. I had the SIM card in the wrong way round and it wasn’t until I read the above post that I realised
    2. When being used on the bench it would appear that you need to ensure that the VDD pin is powered as well as the 0V and 5V power inputs. Until the VDD pin was connected it failed to connect to the network.

    I’d be interested to know if you had VDD connected on yours tmg745?

  20. @Matt

    I too have an EVB in addition to the standard SIM800L board. I don’t have VDD connected on the EVB. It just reads 2.6V once the board is up and running, which is the level the RX and TX pins work at. The RST pin reads 4V (the output from the onboard regulator) and you can add a reset for the device by attaching a momentary button between the RST pin and the adjacent GND.

    The secret is, I think, using quite large capacitors (1000uF) across both the external input voltage (9V battery for example) and also across the output from the 5V fixed regulator 7805 (or LM317/LM338 adjustable regulator for the standard SIM800L, with R1=200 Ohm and R2=470 Ohm to give 4.19V supply).

    I can only get reliable operation with these capacitors connected.

  21. @tmg745
    you are right about the capacitor: I just added one 1000uF over the original yellow polarised tantalum and got it working.
    No change to test with Texecom.
    Since you have both china-red led and uk-green led: do they react different at general comments concerning extra prelude LF CR before the actual answer?

  22. Hi all

    Quick question.
    Can’t the port from the controller power the SIM800L ?
    How many volts does it output?
    Because it does power all other modules such as comwifi/com2400…

  23. The panel runs at 12V where as the modules are usually 5V, hence the need for a regulator to step it down. The genuine parts presumably include a regulator as part of the package or else are designed to work at 12V natively. You can get the regular boards very cheaply on ebay from China and they don’t take up too much room so it’s well worth it.

  24. I’ve successfully completed my equivalent SIM800L set up and all working. Because the evaluation board uses crude voltage control in the form of two diodes to drop a volt and a half to allow use with 5 Volt Arduinos or similar, I’ve bypassed this and used a small switch mode converter set to 4 volt (so the conversion is from the panel at 12 volt down to 4 volt, rather than 12 volt to 5 volt to 4 volt via the diodes), this is much more ideal for supplying power as the diode method isn’t a regulator and so the voltage will fluctuate based on current drawn via the diode method, so could give rise to some instability.

    Here is the finished board, and I’ve mounted the regulator and the SIM board on a prototype board and added a connector. The diodes can be seen bypassed top left of the blue board with a white wire from one side of the diode looping underneath the join the other diode so shorting them out. I also added an electrolytic capacitor that is 100uf for good measure.

    All good fun. I had all the parts apart from the SIM board which I bought for £12.00 on Ebay, so a big saving from £150.00 on the official ComGSM, plus this mounts inside the case so neater.

  25. Good work! Very neat and tidy and also I’d not realised the finer points of the electronics. Having said all that my setup has worked well so far and there’s no sign of instability as yet. I much prefer having everything mounted internally, and in fact it surprises me that Texecom don’t make more effort to provide this. They give you a nice solid anonymous steel case, and the expect you to surround it with a load of plastic boxes saying Texecom all over them! I suppose the idea is that you may not put the boxes next to each other. Even so I bet a lot of people do. I might ask them about this one day…

  26. Gentlemen,

    I did receive my SIM800L board and i’m waiting for the voltage regulator.
    Where do you power the voltage regulator that will supply 5V to the Sim800L?

    The only one i can come up with is the +12 AUX. Do you think it can handle the Voltage regulator->Sim800L since it’s capped at 1A?

  27. Hi, the ideal place to power it is from the same com port connection, with the first pin, the one on it’s own, being 12 volt, just take it from there. Not sure what you mean by capped at 1 amp. The SIM800L will not use anywhere near that much power for sending text messages. It will draw quite a bit of power however that draw is high for only very short periods of time in fractions of second, so over time it’s not using much. This is where the power supply and regulation is important as it needs to regulate very very quickly.

    The wires from the regulator to the SIM800L should be as short as possible. It will not be too reliable with a standard linear regulator though, like a 7805, as these struggle to react quick enough and will waste a lot of power as heat as they basically burn off the extra voltage. Hopefully you mean you are getting a DC to DC convertor, these ones are ideal as they work at a very high frequency so are small and efficient ( are designed for this sort of task, of course you need a volt meter in order to set the output voltage to 5 volts.

    Good luck.

  28. Hi

    That is a linear voltage regulator which means it is pretty inefficient and will run quite hot (why it comes with a heat sink) and may not be too reliable, it’s similar to the 7805 I mentioned but adjustable. I would recommend the one I linked to as it is small and very efficient, it will not get hot and is similar if not identical to the design they use in the official ComGSM and all manner of similar digital products.

    ALiExpress do one very similar and cheaper than the linear one



  29. Such a great blog, already built the usb-com from your posts/direction and now keen to get SMS over gsm working properly (would be easier than using the pstn com2400)

    Just to confirm I need to buy a SIM800L and an appropriate voltage regulator module to step down the 12v pin1 provides to a steady 3.3-4.7v

    Is the rest just plug and play or is any jiggery-pokery necessary?

  30. Thanks!

    Yes this is pretty much it. There have been some interesting ideas about alternatives to the DC-DC converter I used which I’ve covered in the most recent post so do have a look at it. There do appear to be some variations in the SIM800L modules and some people have had problems, but mine worked without any issue so I’d recommend it.

    Once connected don’t forget to configure the port using Wintex and then you should be all sorted. You can check if it is working through Wintex as it will show you the signal strength etc.

    Please let me know how you get on!

  31. “Just to confirm I need to buy a SIM800L and an appropriate voltage regulator module to step down the 12v pin1 provides to a steady 3.3-4.7v”

    I would definately recommend the one I’ve linked to further up in the comments as it’s much smaller and more efficient than some other similar regulators (tip, they are pretty cheap so buy a couple in case one is faulty). You also need a voltage meter in order to adjust the voltage regulator to the correct output voltage, I would recommend going for the middle ground of around 4 volts. Keep the wires as short as possible between the regulator and the SIM800L.

  32. Hi,
    its an MP1584 DC-DC ‘Buck’ converter i’ve got on its way to me, multimeter and soldering iron are all at the ready!
    @phil – can i ask where you placed the capacitor and its spec?

  33. The capacitor used was a low series resistance type electrolytic, usually sold as ‘LSR’ at 100uF, voltage wise 6 volt would do but bit higher is fine. Just make sure if it is less than say 15 volt that you have adjusted the voltage down first on the regulator just so you don’t fill it with 12 volt prior to adjustment.

    Fit the capacitor as close to the VCC and GND pins as you can. It probably isn’t necessary to have it but it certainly would not do any harm.

  34. Some of you reported an issue with the leading CR and LF.
    Looking to the SIM800 commands it looks like you can remove those with the ATV command
    ATV0 and ATV1
    0 –> Information response:
    1 –> Information response:

    Just a thought…


  35. managed to get it all soldered up and ready a while back, just having trouble with giffgaff giving sufficient signal 😦

    are there any other networks people would reccomend?

  36. Got this all up and running on my Premier Elite 48 alongside my Com-IP but I’m now getting Mains AC Alarms showing on my keypad and in the logs every now and then. They go away when I remove my DIY-Com-GSM so I suspect the errors are caused by the Sim800L is drawing a fair bit of current at certain times. I’m using one of these buck converters:

    Anyone else experiencing anything similar?


  37. Hi, I’ve had no problems at all using the DIY GSM.

    What is your power consumption with or without the module? Are you borderline to drawing too much current?

    The module you have is a little bit dated but should be okay. If you have long leads on the output to the GSM module that could be causing noise, or noise could be being introduced back into the system which is causing it to log errors. The module could also be faulty. Also make sure it isn’t being shorted out on anything.

    I would recommend swapping the converter to something more efficient, see posts above, either the one from AliExpress or the one I linked to on Ebay. Keep the supply leads as short as possible. Also a low ESR capacitor, say 10 volt 100uf placed very close to the GSM module power pins may help.



  38. I’ve got a very similar DC:DC converter and it works OK, but this does seem the most likely culprit. I don’t think it’s a current issue as such, unless maybe there is actually a problem with the AC PSU which is being unmasked by the drain from the GSM module? I think as Phil suggests first thing to do is try replacing it and see if the problem persists. Please let me know how you get on?

  39. Hi, great post! Ok trying to get this done but Im seeing ATS path fault on my keypad… There are (4) 1+3 pins on com on texecom premier 24. In guessing the separate one is 12v. What are the next tree? GND, TX and RX? I plugged pins 1 and 2 to voltage regulator ànd then to two DC and the left GND pins on the 800l. Apart from these two, I plugged tx and RX pins to the remaining two pins on com. So I used 4 pins on com and 4 pins on 800l (leaving rst, another gnd and vdd unplugged). I think I programmed the panel properly via keypad. What am I missing?

  40. Thanks!

    There are some details about the pinout of the ports here:

    It depends a bit on the way they have labelled the ports on your 800L as well. Sometimes the labels for TX & RX are swapped over, so if it doesn’t work one way round it’s worth reversing the pins and trying again. So just double check that you are getting the correct pins out of the Texecom board. You will need to supply power to the 800L from some other source (I’m using the Aux 12v out with a voltage regulator).

    You will need to configure the correct port in Wintex, and you also check in one of the diagnostic screens if it working properly. It will show you the signal strength and if this is good (in green) then it means it’s working.

    Can you post which pin on the Texecom is going to which pin on the module?

  41. Hi,

    Thanks for your help. I have connected only 4 pins of my 800l: 5v and gnd through voltage regulator to aux 12v and 0 on the panel. The remaining two pins – tx and RX to com2 right two pins. So com com port has only two pins connected (I tried swapping TX and RX). I also tried to insert SIM card in all possible ways.
    The only config I’ve done was to set com2 and comgsm. GSM signal is -113dB no matter what (antenna is plugged). Maybe my gsm800l is broken :/

  42. Don’t forget to connect the GND from the 800l serial port to the corresponding pin on the alarm (pin 3, so the middle one). This may well be why it’s not working. You get the -113 if it’s not working, you will get that even with no module!

  43. Ah, that was a good hint! It’s -93dB now but still not working. Doesn’t answer to my text messages and does not do a test call. This might be due to difference in AT commands discussed earlier… :-/

  44. Hmm OK, that’s a shame. The fact you are getting a different signal strength shows that it is definitely communicating. Are you sure you have set it up properly in Wintex? There quite a few options and you need to configure your mobile number as the place to send text messages. I don’t think it will reply to you unless this is done.

  45. I think I may have an idea why it is not working. I installed UK’s Three sim card which supports only 3G and 4G. I think the GSM800L module works on 2G. Anyone tried Three? I’ll buy some other sim card today and try!

  46. Yes this might well be it, I think it does only use 2g. I use Giffgaff which works fine. You do need to make sure the card is set up in a phone and registered before you put it in the module

  47. It’s working! I put EE sim card and it works like a charm! Thanks for you help. It’s a little bit slow to be honest, I wonder if original ComGSM is faster. If I sent [pin] status it takes about 30 seconds to get the response.
    I’m pleased anyway, I will put one more com in and should be fine! 🙂

  48. Hi, good to hear you got this working. I’m using with O2 and the delay is minimal, so it is possibly just a delay on EE networks to your phone. It will operate the same speed as the original ComGSM give or take. Regards Phil

  49. That’s great – so pleased you have got it going! The speed of response sounds pretty similar to what I have seen, and I don’t think that’s anything to do with the interface. I think it is just to do with how quickly the messages are exchanged and also down to the mobile phone network. I wonder if 2G networks are treated any differently by the phone companies these days, perhaps they are given a lesser priority? For the COM port see my other posts about adding in a third port.

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