Very simple Twincat2 Mqtt Function Blocks

I use this very simple function blocks to control a floor in our house. As broker i use Mosquitto. "Smart home" is done with OpenHab. Alexa is also working a bit thanks to OpenHab.

Uses MQTT Version 3.1.1. See http://docs.oasis-open.org/mqtt/mqtt/v3.1.1/os/mqtt-v3.1.1-os.html.

It does not send the DICONNECT telegram!
No last will, not QoS, not HTTPS, no nothing.

My CX8090 needs around 30ms cycle time with about 210 publish and about 230 subscribe calls (used global search).

Needed TwinCat libraries

TcpIp.lib TcUtilities.lib

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DataTypes

ST_MQTTSETTIGNS

Stores the MQTT settings used for the function blocks.

ST_MQTTTELEGRAM

Holds a single MQTT telegram (raw data).

ST_MQTTRECEIVEDPUBLISHTELEGRAM

Holds a decoded MQTT telegram and used internal.

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POUs

Intern

Function block for internal usage.

FB_MQTT_CONTROLLER

Controls the connection to the MQTT broker. When bActive is TRUE it starts a connection. Sends and receives the data. Must be called every PLC cycle.

Inputs:

bActive = Use MQTT (connect to the broker)
sMqttClientId = A client id like "MyMqttClient"
sMqttUserId = A user id for the broker connection ('' = none), defaults to '', caution: transmitted unencrypted
sMqttPassword = A password for the broker connection ('' = none), defaults to '', caution: transmitted unencrypted
sMqttBrokerIP = The IPV4 address from the broker
nMqttBrokerPort = The port from the broker, normaly 1883

Outputs:

bBusy = The function block is doing something

InOut:

stMqttSettings = A global variable for the datatype ST_MQTTSETTINGS

If there is a valid connection, bValidConnection in ST_MQTTSETTINGS is TRUE.

FB_MQTT_PUBLISH

Send a value for a topic. On the first call it will publish the value from sValue. The it checks every call if the value has changed. When this happens, it sends the new value. Must be called every PLC cycle.

Inputs:

sTopic = The mqtt topic to publish on
sValue = The value which will be sent
bRetain = See http://docs.oasis-open.org/mqtt/mqtt/v3.1.1/os/mqtt-v3.1.1-os.html#_Toc398718037, defaults to TRUE

Outputs:

bBusy = The function block is doing something

InOut:

stMqttSettings = A global variable for the datatype ST_MQTTSETTINGS, use the same you used with FB_MQTT_CONTROLLER

FB_MQTT_SUBSCRIBE

Subscribe to a MQTT topic and receive data. Must be called every PLC cycle.

Inputs:

sTopic = The mqtt topic for the subscribtion
bAccept = When FALSE, subscribe but do not set bNewValue output

Outputs:

sValue = The received value
bNewValue = A new telegram for topic has arrived. The function block does NOT check if the value is different to the last recevied value for this topic.
bBusy = The function block is doing something

InOut:

stMqttSettings = A global variable for the datatype ST_MQTTSETTINGS, use the same you used with FB_MQTT_CONTROLLER

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Sample OpenHab item

Below is a sample for a light or switchable plug. Old Mqtt1 plugin.

Items file (Filename: something.items in items directory)

Switch Light "A room name"
(Group1, Group2)
[ "Lighting" ]
{
mqtt=">[plc:theMqttTopicUsedReplaceWithYourOwn:command:ON:1],>[plc:theMqttTopicUsedReplaceWithYourOwn:command:OFF:1],<[plc:theMqttTopicUsedReplaceWithYourOwn:state:MAP(onoff.map)]",
autoupdate="false"
}

Mapping file (Filename: onoff.map in transform directory)

0=OFF
1=ON