Compatible meters

Work Cycle

The Bridge has a simple work cycle that consists of five phases.

Initial Phase

This is the phase that is executed after the device is started of restarted. The Bridge performs a quick self test which you can easily spot by the green internal LED flashing. After that, the configuration is evaluated. If successful, the LoRaWAN Join phase is executed next.

LoRaWAN Join Phase

If the Bridge is configured to use over the air activation (OTAA), the OTAA join is performed at this point. The device will repeatedly try to join its LoRaWAN network until the process is successful. It then enters the Data Collection Phase. If the Bridge is configured to use ABP instead of OTAA, this phase is left immediately and the Data Collection Phase is entered according to the cron configuration.

The retry for the LoRaWAN Join starts at 30 seconds plus a random jitter of up to 10 seconds and doubles with every try up to a maximum of 8 Hours plus a random jitter of up to 10 minutes.

Data Collection Phase

During the wMBUS collection phase the device receives any wireless M-Bus data with valid CRC and stores it (without DLL CRCs) for the following LoRaWAN upload phase but only if the received telegram passes the user defined white list filters. Similar telegrams of one identical meter may be received multiple times during this phase. In this case the newest telegram with the same id, type and length will replace the previously received one. Only the latest telegram will be uploaded via LoRaWAN. After the configured amount of time for collecting data the LoRaWAN data transfer phase is entered.

Data Transfer Phase

During the Data Transfer Phase the Bridge uploads all previously stored wMBUS data using LoRaWAN. All wMBUS DLL (Data Link Layer) CRCs are removed before the LoRaWAN upload since LoRaWAN has it own data integrity checks. Depending on original wMBUS telegram byte sitze this can require multiple LoRaWAN messages to be sent. Since LoRa requires any device to respect a strict duty cycle, it is possible, that the Bridge will need to wait before sending its messages. If this happens, the device will enter a power saving modus while waiting for the next message. It is possible that transferring all data will take several minutes. In addition to the wireless M-Bus data, the Bridge sends a status packet once a day during this phase. The status packet will always be transmitted prior to any data packets. For a detailed description of the data sent refer to chapter "Data Packet".

Sleep Phase

After transferring all data packets the Bridge enters the Sleep Phase. During this it is completely inactive to avoid wasting power. It remains sleeping until one of the cron expressions given in the configuration triggers. When that happens, it enters the Data Collection Phase again.

The wMBUS LoRaWAN Bridge

Hardware revision 2.x (active since 2020)

Hardware revision 1.x (active since 2017)

Hardware differences

The main differences between hardware revision 1.x and revision 2.x are:

• HW1.x has an additional on board temperature sensor (seldom used)
• HW1.x is available in a 2x AA cell (1.5V) variant with compact housing (rarely requested)
• HW1.x may be combined with external power supply addon (5V...30V)

So the main reason to request revision 1.x is the smaller housing with two AA batteries or the need for an external power supply. The same firmware will always provided for both hardware revisions.

Device installation

The device must be fixed on a flat surface using the lateral mounting holes of the case, see chapter "Housing Dimensions" for a detailed description of all housing dimensions. Alternatively we offer as accessory a mounting clips.

For optimal RF performance (e.g. LoRa range) any metal obstacles near the internal antenna should be avoided. In this case 'near' is defined as keep-out distance of about 3-5 centimeters around the antenna. The internal quarter wave monopole antenna can be identified by the pcb trace near the white printed encircled 'connectivity' symbol. In any case a device mounting directly on top of a metal surface is not advisable since it will degrade the possible RF range. Stone walls, wood or plastic standoffs are perfectly ok.

In case of challenging installation locations (e.g. in basements) or unavoidable long distances to the next LoRaWAN gateway, Lobaro offers on request custom product variant equipped with a 'SMA' connector to support a external antenna connection.

Power Supply

The wMBUS over LoRaWAN Bridge default power supply consists of one connected 3.6V 'D' sized battery equipped with a JST XH 2pin connector.

• Size: D-Cell (34mm x 61.5mm)
• Connector: JST XH series
• Voltage: 3.6V
• Operating temperature: -55°C...+60°C
• Li-SOCl2 (not rechargeable)

Battery life time

The battery life time of the wireless M-Bus to LoRaWAN Bridge can not be specified trustworthy without knowledge of the detailed installation scenario. At least estimations for the following custom project based parameters have to be known:

• Meter count per single wMBUS bridge, e.g. 10 different meters.

• Needed LoRaWAN transmission interval, e.g. daily uploads.

• Average wireless M-Bus telegram size in bytes, e.g. 35 byte.

• Wireless M-Bus telegram transmission interval of the meter, e.g. every 10 seconds.

• Typically used LoRa Spreading Factor / LoRa link quality, e.g. SF10.

Depending on these parameters battery life times from a few months to over 15 years can be achieved. You may send us your use-case details as described above to support@lobaro.com and we will return to you a custom battery lifetime calculation, a recommendation for the best power supply scheme and the needed minimal battery capacity.

Example calculation

In this battery lifetime calculation scenario the target meters send a 35 byte long ('L-Field') wireless M-Bus telegram constantly every 10 seconds. A real world image of a 4:1 (4 meters, 1 bridge) configuration can be found at the top of this documentation. The meter transmission interval is for example very similar to a 'Hydrus' ultrasonic water meter of Diehl Metering. The Diehl meter itself has a specified battery life time of 12 years.

Because of the mentioned 10 second send interval it is sufficient to configure the bridge for a wireless M-Bus listen period of 20 seconds by setting the bridge configuration parameter cmodeDurSec to a value of 20 (refer to section "Configuration"). This will ensure that all four meters of interest send their consumption telegrams at least once during the configured listen period of the bridge.

For this example battery-lifetime calculation the weakest and best possible LoRaWAN connectivity will be compared. Weak means to reach a LoRaWAN Gateway the Lobaro bridge has to send its LoRaWAN uplinks very slowly (≥ 2 seconds) and redundant by using LoRa spreading factor 12 (SF12). Estimations for the opposite situation with a excellent LoRa link quality and thus the possible usage of SF7 have been calculated too. In both coverage scenarios covered the actual usable battery capacity has been set to 80% of the nominal value of 19Ah for the "D" sized mono 3.6V cell. The resulting worst-case minimal battery-life times in years for both coverage situations are presented below:

Worst-Case Battery life with daily uploads of x meters using LoRa SF12 and SF7:

Usage scenario recommendations

As a simple rule of thumb using the Lobaro wireless M-Bus over LoRaWAN bridge is a good fit in applications that require daily (or less often) consumption values of 1 to 40 installed wireless M-Bus meters. For installations with a higher meter count simply more Lobaro bridges may be used.

Another key factor for high battery lifetime is to select or configure your wireless M-Bus meters in a way that they send short telegrams very frequently, proven good values are periods smaller than 30 seconds and telegram sizes smaller 50 bytes. This helps to minimize the needed wMBus listening time period and avoids the need for multiple LoRaWAN packets per single telegram (data splitting).

Beside this the bridge is naturally most economical when multiple meters per single bridge can be collected and forwarded via LoRWAN. Although for some applications a 1:1 setup, e.g. one bridge per meter, may deliver enough benefits to justify the invest.

For hourly or even more frequent meter data uploads, as requested by some of our customers, LoRaWAN isn't the perfect match from a technology point of view. The same holds for scenarios where hundreds of meters are expected to be transferred by a single bridge, e.g. in 'sub-metering' applications with tons of installed heat cost allocators. For such more demanding cases Lobaro can offer better solutions using higher bandwidth transmission techniques like NB-IoT (Narrowband IoT).

Configuration

The (initial) configuration is normally done using our free Lobaro Maintenance Tool and the USB PC configuration adapter to be connected to the "config" connector on the hardware.

Beside this the configuration can also be changed or read remotely in the field using LoRaWAN downlink messages.

LoRaWAN

The connection to the LoRaWAN network is defined by multiple configuration parameters. This need to be set according to your LoRaWAN network and the way your device is supposed to be attached to it, or the device will not be able to send any data.

For a detailed introduction into how this values need to be configured, please refer to the chapter LoRaWAN configuration in our LoRaWAN background article.

wMBUS bridge

^† See also our Introduction to Cron expressions.

Uplink Payload formats

After collecting wireless M-Bus telegrams over the air, the Bridge starts uploading data via LoRaWAN. There exist two data formats that are transmitted over different LoRaWAN ports. As LoRaWAN can only transmit very short messages, the message formats contain only data bytes. The meaning of a byte is determined by its position within a message. The following describes the package formats used by the wireless M-Bus Bridge.

M-Bus telegrams can be longer as the maximal size of a LoRaWAN-Message. For this cases, the Bridge needs to split a telegram into multiple pieces and upload it using multiple LoRaWAN-Messages. There are two different methods this is done, according by the Payload Format you set in the Bridge's configuration.

Payload Format 0 is focused on easy reassembly of the pieces. The parts are encoded by port numbers and the data can just be concatenated together. Payload Formats 1 and 2 add additional information to the telegram. They focus on putting as much of a telegram in a single LoRaWAN-Message as possible with respecting the current Spreading Factor.

Status Packet

Port 1 - In order to provide some information about the health & connectivity state of the device itself, the device sends a status update at a daily basis. The status packet is sent on the first upload phase after activation of the device (after reboot) and then repeatedly in every upload phase that takes place a day or longer after the previous status packet. It has a length of 7 or 8 bytes. The battery voltages and ambient temperature are encodes as 16 bit integer using little endian encoding.

We provide a JavaScript reference implementation of a decoder for this status packet on GitHub, which can be used directly for decoding in The Things Network.

Data Packet (Format 0)

After each wMBUS collecting phase, all saved telegrams (up to 500 can be stored) will be uploaded via LoRaWAN uplink messages as fast as possible. The received wMBUS telegrams that did pass the configured white list filters will be uploaded without any modification in one or more LoRaWAN messages. If a wMBUS telegram is bigger than the bridge configuration parameter loraMaxMsgSize the transmission will be done using multiple LoRaWAN messages. This parameter is limited to ≤ 50 bytes due to LoRaWANs maximum payload size restrictions. In case of telegram splitting is needed the receiving backend application server as to reassemble the original wMBUS telegram before decryption & parsing of the meter data. This is done by simply joining the messages together in the order of receive. The LoRaWAN port encodes identifies a LoRaWAN fragment of the original wireless M-Bus telegram. This way partial messages can be identified using the LoRaWAN Port:

• 10 < LoRaWAN Port < 100 ≡ (Part Number | Total Parts)

Gaps in the LoRaWAN Frame Counter are giving a hint for missing telegram parts which can happen in LoRaWAN since it's a ALOHA based protocol, e.g. collisions and some packet losses are accepted by principle of operation. In case the backend noticed a missing packet the wMBUS telegram can't be assembled anymore as described before.

Examples

Examples (with loraMaxMsgSize = 50):

• A 48 Byte wMBUS telegram will be send on LoRaWAN port 11. Port 11 says it is the first message of only one message (no splitting).
• A 75 byte wMBUS telegram will be send in two messages on LoRaWAN ports 12 and 22. Port 12 means this part one of a wMBUS telegram that got splitted into two LoRaWAN messages. Port 22 means that this data is the 2^nd part of the original wMBUS data. Both parts have to been concatenated in the order of receive by the backend.
• A 101 byte wMBUS telegram will be send in three messages on LoRaWAN ports 13, 23 and 33. Port 13 means this part one of a wMBUS telegram that got splitted into three LoRaWAN messages. Port 23 means that this data is the 2^nd part of the original wMBUS data. Port 33 means that this data is the 3^rd part of the original wMBUS data. All three parts have to been concatenated in the order of receive by the backend.

Data Packet (Format 1)

When using Payload Format 1, collected telegrams are uploaded on a single Port: 101. For each telegram there will be added the timestamp of reception. The first byte of messages on Port 101 encodes splitting of messages as follows.

Splitting

Every Uplink on Port 101 is prefixed with a single byte, where the least significant Bit indicates if that Uplink is the first part of a message, and the second least significant Bit indicates if that Uplink is the last part or a message. So there are 4 different possible values for the first Byte of an Uplink on Port 101:

So each message sent on Port 101, whether it is contained in a single Uplink or spread over multiple ones, starts with an Uplink where the least significant Bit of the first Byte is set. Each Message ends with an Uplink where the second least significant Bit of the first Byte is set. In cases where the Message fits in a single Uplink, that Uplink is both first and last Uplink, and therefore both Bits are set.

The combination of those two Bits and the Frame Counter of the Uplinks makes it possible to upload Messages of any length while allowing the receiving side to now exactly, if a Message has been transferred completely, or if part of it is missing (when there are Frame Counter values missing).

The Bridge puts as many Bytes in each Uplink as possible for the current Spreading Factor, even if the Spreading Factor changes between Uplinks because of ADR.

When the data of all Uplinks that are part of a single Message are appended in order of reception (after removing the first Byte of each Uplink), you get the payload Data of a full message.

Payload (Format 1)

The Payload Data after reassembly of the split parts consists of a 5 Byte Timestamp, that marks the point in time the Bridge did receive that telegram, followed by the Data of the Telegram. The Timestamp follows the convention of all our 40bit-Timestamps; you can find the details under Timestamp in our LoRaWAN Background Information.

Examples

For easier understanding, the wMBus-Telegram in the examples will always be 0102030405060708090a0b0c0d0e0f.

A message sent in a single Uplink

A message split over two Uplinks

A message split over three Uplinks

Missing a Part

Data Packet (Format 2)

Upload Format 2 works like Upload Format 1, with the same logic for splitting messages, but uploads are sent on Port 102. The Payload consists of a 5 Byte Timestamp marking the time of reception, followed by a uint_8 that holds the (negated) RSSI value for that reception, followed by the Data of the Telegram.

Examples

Upload Speed / Duration

The bridge has to work in compliance with the European SRD 868 1% duty-cycle regulations. This implies as a rule of thumb the device can upload at most wMBUS telegrams via LoRaWAN for 36 seconds every hour.

The actual transmit time ('ToA: time on air') for each LoRaWAN message depends on the byte size and the used LoRa spreading factor (SF) which defines how redundant LoRa data is send. This means a device with good connectivity and consequently using LoRa SF7 (ToA ≤ 0,050s) can upload much faster more data than a node using LoRa SF11 (ToA ≥ 1s) due to a hard to reach LoRaWAN gateway. The bridge will upload in conformity with the regulations automatically as fast as possible. When it has to wait it enters a low power sleep mode until the next transmission is possible again. The next data collection phase will be started only after completion of the previous upload phase in respect to the configured listenCron parameter. Because of this it is advisable to define the cron parameter with an estimation of the upload duration in mind. This will avoid unexpected 'skipping' of data collection phases.

Downlink Payload formats

Update Configuration

Update of Configuration parameters is documented in our LoRaWAN downlink messages documentation.

Ad-hoc readout

Triggers an Ad hoc readout, independent of CRON triggers. The Ad-hoc readout is using the same parameters as a CRON triggered readout.

Downlink Message:

• Port: 132
• Message: read (ASCII Encoded) Hex: 72656164 Base64: cmVhZA==

Decoding wMBUS telegrams

After receiving the raw wireless M-Bus telegrams from your LoRaWAN network provider the actual metering data has to be decrypted and decoded by a backend service for further processing. The details of this are described in the EN 13757 norm and the newer OMS specification, which is a clarification of the original underlying norm.

A universal wireless M-Bus decoder is a relatively complicated piece of software if you start implementing it from scratch since the norm covers many different use cases, units, meter types and data formats. If you know in advance the exact telegram format of the deployed meters in your setup a hard coded data decoding may be a feasible approach. This is because wireless M-Bus devices often send the same telegram format in every transmission. Please contact the manufacturer of your meters for the needed telegram format details.

An an alternative to support a quick evaluation of our hardware Lobaro offers a easy to use webservice which is designed to decode all sorts of wMBUS input data including decryption if the correct key has been provided. You can access the decoder service for free during testing. The API can be licensed for production usages.

Optional: Lobaro IoT Platform

The bridge can also be integrated in the Lobaro IoT platform with the following benefits:

• wMBUS data reassembling from raw (partial) LoRaWAN uplinks
• Wireless MBUS data decryption
• Device management including remote configuration
• Std. Web APIs to connect external services
  • REST
  • MQTT
  • HTTP Push
  • CSV Exports
• LoRaWAN data import from many common LoRaWAN network servers:
  • TheThingsNetwork (TTN)
  • ShirpStack
  • Element-IoT
  • Actility
  • Loriot
  • Firefly
  • Everynet

Technical characteristics

Product
Type name	LOB-GW-WMBUS-LW-2
Description	Lobaro Wireless M-Bus Bridge V2
RF transceiver
Chipset	Semtech SX1272
Frequency Range	863 to 870 MHz
TX Power	≤ 14 dBm
LoRa communication
LoRaWAN Protocol	Class A  LoRaWAN 1.0.2 EU868 (certified) Class A  LoRaWAN 1.1 EU868 (experimental)
Activation method	Over-the-air activation (OTAA) Activation by personalization (ABP)
Encryption	AES128
Typically RF range	≤ 2km
Ideal RF range	≤ 10km (free line of sight)
Wireless M-BUS communication
Supported Modes (EN13757-4)	S1, C1, T1
Frequencies	868.3 MHz, 868.95 MHz
RF Range	≤ 30m
Telegram memory	32KByte (for up to 500 wMBUS telegrams)
Power Supply
Nominal Supply Voltage	3.6V
Supply Voltage Range	2.2V - 3.7V
Power supply	3.6V ER34615 3.6V battery
Current consumption @3.6V
Normal	≤3 mA
Wireless M-BUS RX	≤14 mA
LoRa RX	≤14 mA
LoRa TX	≤80 mA
Sleep with RTC running	≤15 µA
Mechanical dimensions
Size	122 mm x 82 mm x 55 mm
Housing Material	Industrial polycarbonate
Rating	IP67
Environmental Requirements
Operating temperature range	-20°C to +55°C
Max. Installation height	2m
Conformity

Specifications of hardware revisions v1.x can be found in the previous documentation.

Housing Specification & Accessories

The Lobaro wireless Mbus bridge uses the TG PC 1208-6-o feature rich IP67 housing from Spelsberg. For this housing the following accessories are available on request:

Sealing kit (TG PST1):

May be used to seal the box to complicate unauthorized access to the device.

External fixing lugs (TG ABL):

Allow the mounting without opening the (sealed) cover.

CE Declaration of Conformity

• CE Declaration of Conformity - Rev1 HW

LoRaWAN Alliance certificate (HW2)

Quick Start Manual (Deutsch)

Example Parser

TTN

function readVersion(bytes, i) {
    if (bytes.length < 3) {
        return null;
    }
    return "v" + bytes[i] + "." + bytes[i + 1] + "." + bytes[i + 2];
}

function Decoder(bytes, port) {
    // Decode an uplink message from a buffer
    // (array) of bytes to an object of fields.
    var decoded = {};

    if (port === 9) {
        decoded.devStatus = bytes[0];
        decoded.devID = bytes[1] | bytes[2] << 8 | bytes[3] << 16 | bytes[4] << 24;
        decoded.dif = bytes[5];
        decoded.vif = bytes[6];
        decoded.data0 = bytes[7];
        decoded.data1 = bytes[8];
        decoded.data2 = bytes[9];
    }

    // example decoder for status packet by lobaro
    if (port === 1 && bytes.length == 9) { // status packet
        decoded.FirmwareVersion = String.fromCharCode.apply(null, bytes.slice(0, 5)); // byte 0-4
        decoded.Vbat = (bytes[5] | bytes[6] << 8) / 1000.0; // byte 6-7 (originally in mV)
        decoded.Temp = (bytes[7] | bytes[8] << 8) / 10.0; // byte 8-9 (originally in 10th degree C)
        decoded.msg = "Firmware Version: v" + decoded.FirmwareVersion + " Battery: " + decoded.Vbat + "V Temperature: " + decoded.Temp + "°C";
    } else if (port === 1 && bytes.length == 7) {
        decoded.FirmwareVersion = readVersion(bytes, 0); // byte 0-2
        decoded.Vbat = (bytes[3] | bytes[4] << 8) / 1000.0; // originally in mV
        decoded.Temp = (bytes[5] | bytes[6] << 8) / 10.0; // originally in 10th degree C
        decoded.msg = "Firmware Version: " + decoded.FirmwareVersion + " Battery: " + decoded.Vbat + "V Temperature: " + decoded.Temp + "°C";
    }

    return decoded;
}