Didactum Monitoring Systems
Setting up Modem, SMS Commands & GPS

Didactum monitoring systems (models 50T, 100T, 500T and 550T) can be equipped with a GSM or 4G/LTE modem. This enables sending SMS notifications, remote control of the device via SMS commands and – with compatible LTE modems – using an internet connection as a failover solution as well as GPS positioning.

The modems operate in Primary mode. If Primary mode is not available (e.g. no 4G reception), the modem automatically switches to Secondary mode (2G).

Task: Send alarm messages until the alarm is deactivated via SMS command or the conditions change.

To implement this, a Trigger element is used as an intermediate step. The trigger is activated ("on") when an alarm occurs and deactivated ("off") when the condition returns to normal. As long as the trigger is active, notification and call actions are executed. The trigger can be deactivated via an SMS command when the notification is no longer needed.

Step 1 – Create Trigger Element “Trigger Alarm”

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Create a new Trigger element named “Trigger Alarm” in the System Tree panel. This element serves as an intermediate storage for the alarm state.

Step 2 – Logic scheme for controlling the trigger

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Create a Logic scheme (Preferences → Logic schemes) that switches the trigger on when the alarm occurs and off again when returning to normal state.

Step 3 – Logic scheme for notifications

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In case of alarm, an SMS is sent (notification element “SMS to Admin”) and then a call is triggered to the stored number (call task “Dial to Admin”). The call is repeated every 10 minutes according to the “Repeat/Duration” field until the alarm is reset. The SMS is sent only once.

Step 4 – Deactivate alarm prematurely via SMS

To deactivate the alarm prematurely once the notification has reached the recipient and no further messages are needed, the “Trigger Alarm” must be switched off. Enter the permitted phone numbers in the “List of allowed phone numbers” field on the “SMS messages” page. Then send the following SMS:

Devices without their own GSM/4G modem (e.g. a Didactum 50T without modem option) can send SMS notifications via another Didactum device equipped with a GSM modem (so-called SMS Gate).

With this function, incoming SMS can be received and their content forwarded to other phone numbers or email addresses. The settings are located on the “SMS messages” page, tab “Incoming”.

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On the right side, a list of all incoming SMS is displayed. Here you will find the central settings for SMS forwarding and SMS commands.

Available Settings

SMS Commands for Remote Control

SMS commands allow remote control of the monitoring system: reading system status, sensor values and group values as well as switching relays (outlets). Authorized phone numbers are entered under Main menu → SMS messages → List of allowed phone numbers.

1. Read Status: get

Syntax: get [ID] or get [Name] – ID is the element ID number, Name is the name of the element. “get” is not case-sensitive (also Get, GET possible). The name must be in quotation marks, is case-sensitive and must be unique.

The reply SMS contains the status of the requested sensor or relay.

2. Switch Relays / Outlets: set

Syntax: set [ID] [state] or set [Name] [state] – state can be on (switch on) or off (switch off). The name is case-sensitive.

Reply: The element (Elementname) was switched on or ... was switched off

3. Relay Pulse: set ... pulse

Syntax: set [ID] pulse {Duration} or set [Name] pulse {Duration} – Duration is the delay in seconds (range 1–120). If no duration is specified, the previously set value is used. The command toggles the relay twice (pulse) with the specified delay.

Reply: The element (Elementname) was switched

4. Control Logic Schemes: logic

Syntax: logic [ID] [state] {Duration} or logic * [state] – ID is the logic number (* = all logics), state is on or off, Duration is the deactivation time in seconds (only for single logic). All fields are not case-sensitive.

Reply: OK

This section is aimed at technically experienced users and integrators who want to manage user accounts and permissions directly via the API or set up central authentication via a RADIUS server.

Permission Concept

Each user profile can access system resources with read-only or read-write permissions. Each resource has an access identifier; access control is done via comma-separated lists of identifiers.

Important server resource IDs (selection): accesskeys, cameras, canbus, devvirt, elements, groups, gsm, log, logics, modules, notify, relays, sdcard, system, users, view as well as all (full access to all resources).

For group permissions (GRead/GWrite) the following also applies: all = full access to all groups, none = access completely denied. By default, elements are not assigned to any group – access is then only possible with all.

Authentication & Session

During login (querytype=auth, fields name and password hash h) the client receives a Session Key (k), which is used to authenticate all further API calls. Alternatively, login via PIN code is possible (querytype=authpin, fields name and n, 4–8 digits).

The session is terminated with querytype=authclose and passing the session key. After a system restart, all sessions are lost – a new login is required.

Reading, Creating and Deleting User Accounts

Central Authentication via RADIUS

Alternatively to the local user database, login can be done via an external RADIUS server. Login is two-stage: First the user is searched in the local database; if not found, a request is sent to the RADIUS server.

Vendor-Specific Attributes (Vendor Code 39052)

On the RADIUS server, the manufacturer-specific dictionary dictionary.local must be placed in the directory /etc/raddb/ and included in the main dictionary file.

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In the policy settings: Delete standard RADIUS attributes. In the area “Vendor Specific” → Vendor: “Custom” → Vendor Code: 39052. Enter attributes by number (see table below).

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Result: All users in the group “RADIUS Group” receive full administrator access to the Didactum unit. For different rights on different devices, separate policies with NAS-IP address conditions can be created.

Example Configuration Files

Check if the modem is ready for operation

1. Insert the SIM card into the modem. Ensure there is sufficient credit or a valid LTE contract.
2. Make sure the external antennas are attached to the modem – both “MAIN” and “AUXILIARY”.
3. Switch on the system. The modem is automatically detected during boot.
4. If the SIM card is inserted while the system is already on, network registration can take up to 15 minutes.
5. Upon successful modem detection, the menu item “SMS messages” will appear.
6. Check signal strength (example: 48 %).

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The signal strength is displayed as a percentage value (0–100 %). A higher value means better reception.

Send test SMS

1. Click on the “+” to the right of “List of SMS messages” – a window for sending a test SMS will open.
2. Enter the mobile number and message text and click “OK”.
3. The SMS should arrive on the specified mobile phone.
4. A confirmation of successful sending will appear in the web interface.

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Enter the mobile number and test text and confirm with “OK”.

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After successful sending, the system displays a corresponding confirmation message.

Internet connection via LTE

Starting with firmware version 2.7.4, the LTE modem can additionally be used for connection to internet services (VPN, SMTP, FTP etc.) as well as for remote access to the device. The settings can be found under Preferences → LTE.

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Overview of configurable LTE parameters (see table below for details on each field).

For a permanent internet connection, we also recommend using an OpenVPN client: The VPN connection remains active both via Ethernet and via LTE (in case of Ethernet failure) and thus ensures permanent access to the protected network as well as a fixed IP address of the device.

Accessing the device via LTE from the internet

If the SIM card supports a private APN with a static IP address, the device can be reached directly via this IP (inquiry with the mobile provider required). You can find the assigned LTE IP address in the “Network” tab (field “LTE IP address”).

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Overview of the device’s network addresses (see table below for explanation of the individual fields).

The modem is used in the system for sending SMS notifications and receiving SMS commands.

Basic procedure

1. Insert the SIM card into a mobile phone and check functionality and PIN code.
2. Insert the SIM card into the modem.
3. Switch on the monitoring system.
4. Configure the modem (see below).
5. Set up SMS notifications and configure appropriate logic schemes or group notifications.

Modem configuration

Modem configuration is done in the Main Menu → SMS messages tab.

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Overview of all modem properties and setting fields (see table below for explanation of the individual fields).

If a modem error occurs, no SIM card is inserted or the PIN code is wrong, a corresponding message is written to the log queue (“GSM modem: Error, check your SIM card and PIN code” or “GSM modem: modem error, restart smsd”). The message is displayed a maximum of 5 times to avoid filling the log.

The “List of SMS messages” shows up to 100 of the most recently sent SMS (up to 1000 on VT9xx systems). This list is not saved when the device is restarted.

GSM Network Operator List

The operator list is automatically updated at regular intervals after switching on and can be manually refreshed using the button. The retrieval can take several minutes; on success, a corresponding log message appears. If no connection can be established to the selected operator, the modem switches to automatic selection mode. The currently used operator is displayed in the “Operator” field.

GSM Modem Elements in the System Tree

In the “System Tree” menu there are elements that display the status of the modem. These do not affect the state of the “System” element and can be used in logic schemes.

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These elements can be added to groups like regular sensors and used for notifications or logic schemes.

Setting up SMS notifications

Open the “SMS” window in the “System Tree” menu to add a notification recipient:

Click “Save” to apply the settings. Use “Test” to send a test SMS (note: test messages may contain incorrect sensor data for the macros %1/%2 – this is normal for testing purposes).

After configuring the recipient, the event that triggers the SMS must be defined under Preferences → Logic schemes → Add. A maximum of 15 SMS recipients can be stored per logic scheme for one or more events. If more than 15 recipients are needed for the same event, an additional logic scheme with the same input condition must be created.

SMS messages are placed in a queue (max. 100 messages) so that it does not have to wait for the completion of the previous sending. On overflow, already sent messages are automatically deleted. Sending information is logged in the system log.

SMS sending via third-party programs (e.g. cURL)

SMS can also be sent via external programs such as cURL. The following Bash script shows the process for firmware version 2.4.x and higher: Authentication at the web interface, determination of the session key and sending the SMS via the HTTP(S) endpoint engine.htm.

The 4G/LTE Modem supports GPS location information if a suitable GPS antenna is connected. A prerequisite is an inserted SIM card and an existing connection to the GSM network. Older LTE modems also support GPS positioning.

The GPS settings and information can be found under Preferences → GPS.

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Overview of the available GPS settings (see table below for explanation of the individual fields).