Category Archives: GSM Door Entry

GSM Call List AT+CLCC Customer Question (it gets a bit technical!)


When I use my smartphone, the dialing screen turns green when the number I called answers,​ h​ow that’s accomplished? Do you know if your chipset has the hardware ability to determine when the call is connected, like via the gsm protocol stack?

​That​ can’t catch the automated voice messages from the phone company (like “the ​number you ​are calling ​is unreachable”) but it can eliminate the ringing tone and that would be sufficient.

DSP would be better but as you say it can’t be readily nor easily done.


GSM Intercom Question Reply

Ringing GSM Phone

[Note: the customer would like us to stop the 400Hz ringing tone from being audible during a call]

Hi <name>,

The network will tell you some things about the call but often (especially when you use a network reseller’s SIM card) it does not give accurate information.

For example, in the UK a company called Lyca resell the O2 network airtime. When using their SIMs the CLCC data in invalid. This is why we had to offer an option to turn off the voicemail divert command. Normally we detect voicemail diversion by noting when the phone does not ring. If the phone is switched off it will dial then instantly connect to the voicemail service which we can see happening from the CLCC command. We see it going to status 2 to 0 and never getting to 3 which is the ringing status. However, Lyca always show transition from 2 to 0 regardless of whether the phone rings or not and never give a status 3 when the phone is ringing. Basically the network notifications are unreliable.

Our intercom (available here) unit has a connection to the microprocessor from the audio circuit so we can digitize the audio and detect frequencies and whether there is audio or not. This is how we implement the SILENCE command functions.

We could switch the volume down to 0 during status 3 on a CLCC request but this may not work with some networks. That would be the easiest way to do what you require. I’ll look into it

Reply from AT+CLCC    NB:  <call state> is of interest here

+CLCC: <idx>,<dir>,<call state>, <mode>,<mpty>,<number>,<type>[,<alpha>] [<CR><LF>]

<state> 0 Disable CLCC unsolicited indication1 Enable CLCC unsolicited indication
<idx> Integer type, call identification number
<dir> 0 Mobile originated call (MO)1 Mobile terminated call (MT)
<call state> The state of the call0 Active1 Held

2 Dialing (MO call)

3 Alerting (MO call)

4 Incoming (MT call)

5 Waiting (MT call)

6 Released

<mode> Bearer/Teleservice0 Voice Call1 Data

2 Fax

<mpty> Multiparty status0 Call is not part of a multiparty call1 Call is one of multiparty call parties
<number> Phone number in the format specified by <type>. Contains a string of up to 32 characters.
<type> Phone number display format. Type of address octet in integer format (refer to GSM 04.08 [8] subclause 129 Local number






Michael Beaver



What’s new in October

This month we sold out of the GSM autodialer  ( and gate opener boards again.  We made a much bigger batch last time but unfortunately due to some large orders in September this did not cover demand.  We have scheduled another batch to be produced in Decemeber, earlier than planned, so this should not happen again.

GSM Switch

GSM Switch with Volt-Free Relay Output

The lack of the auto dialer has provided us with the opportunity to catch up on a few things from redesigning the office to finishing off some new products.  One product of great interest that I have been working is our latest GSM intercom.  It’s been mentioned before on the blog but this week I have been working on the prototype and have something physical to work with.


GSM GOLD Intercom Development Unit

The finished product should look great as the prototype is very appealing despite it not being assembled correctly by us!  We will be leaving the plastic assembly to the professionals in production.


GSM GOLD Intercom Development Unit showing thickness

The concept was to create a flat GSM intercom which appears flush mounted despite being surface mounted.  It was to feature an internal aerial making installation quick and simple.  The challenge of packaging the electronics found on our existing intercom design (shown below) ( into a 5mm thick PCB was tough but we did it.  I suspect future designs will be even thinner although the limiting factor is the speaker at 5.5mm thick.  With 1mm plastic either side for protection this gives a minimum thickness of 7.5-8mm including the rear seal.

GSM Intercom PCB

1 button GSM intercom PCB

1 Button GSM Door Entry Intercom Video

In the video Michael demonstrates our classic 1 button GSM Door Entry Intercom.  It’s been around a while now and has been refined into a very solid system with excellent audio and an easy to use programming method.

The Advent Controls GSM Door Entry Intercom System Key Features:

  • Internal Aerial for Simple and Fast Installation
  • Simple SMS Programming using Intuitive Commands
  • High Audio Quality
  • Space for up to 384 Numbers
  • Dial-to-Open Access Control
  • Lowest Price GSM Intercom on Market

The system uses a high production volume enclosure with our custom UK designed and built electronics inside.  The design of the enclosure is excellent giving good audio and protection against the elements.  As with all of our products the firmware is written in house and has been refined over time to work seamlessly with every network.

The Intercom is available on our website here for just £149 (£124.17+VAT!)

GSM Intercom

Mobile phone based Door Entry System

Is the GSM Door Phone Entry Intercom System Suitable for Outdoor Use?

In the video we test the Advent Controls GSM 1-Button Door Entry system’s waterproof credentials.  Although officially rated as IP45 the unit is fully waterproof to falling rain despite the carefully designed holes for the microphone, speaker and wiring.

Can the Advent Controls GSM Intercom stand up to the ice bucket challenge?  Can it take a good hosing down?  Should JB find a new job as a fireman or stick to packing boxes?  All is revealed.

A donation was made to the charity RoadPeace

vlcsnap-2014-09-01-12h12m04s247The GSM Door Entry Intercom is available from our website on the following link:

Week Ending 08/08/14…

Just a little post about what is new in the world of Advent Controls.  We’ve had some rough drawings and ideas about a new concept in the design of intercoms in general.  What we want as installers is a nice flush mount finish but without having to spend hours smashing bricks out of a wall.  The simplest installations are simple surface mount units like our basic 1-button GSM intercom (  These are great for a quick installation but ideally for vandal resistance and aesthetic reasons we would prefer flush mounting.

Panel Intercom 1st Iteration

Panel Intercom 1st Iteration

The answer is an ultra thin panel style intercom.  We finally started prototyping the PCBs for this design this week and it’s coming along nicely!  Currently we’re working to an 8mm thick design but who knows how thin these will be eventually.  I really believe this is the future for intercom design as they look fantastic, are simple to fit and are extremely strong solid units.

Designing the Panel Intercom

Designing the Panel Intercom

Electronics wise one of the hardest design aspects we’ve found has been to add bulk capacitance for AC voltage smoothing.  Second to this is the speaker thickness and displaced volume (which affects the efficiency of the audio system).  We do believe we have an answer to this on forthcoming designs which could see the thickness of the unit drop below 5mm!  For now we’re keeping with conventional design and sacrificing ultimate packaging efficiency.

Front Panel Design Layout

Front Panel Design Layout

Troubleshooting Setup Issues for Advent Controls GSM Dialers and Relay Boards

Michael describes the most common problems users have when first setting up the GSM systems.

The installer should set up a master user number (their own phone number) before attempting anything else. However sometimes, if there is a SIM fault or aerial problem, the system will not be ready for this. The video describes the symptoms and how to resolve them.

Of course if any further help is needed please feel free to get in touch with Advent Controls