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Extract and graph an integer of binary data from mqtt topic. [message #1857294]

Sat, 28 January 2023 17:57

Dale DeJager

Messages: 2
Registered: January 2023

Junior Member

I'm not sure if this is the best place to ask this question, but I'm unable to find an active forum to ask about MQTT-SPY. I tried posting in mosquito forum, but got no reply. I would like to extract two bytes of data from a binary MQTT topic and graph the data as an integer. I've tried various solutions to create a formatter or a value expression for the Payload data in the graphing tool. I cannot find documentation for how to create either a formatter or and expression.

With the "help" of ChatGPT I've tried variations of

function format()
{
	byte[] binaryData = receivedMessage.getPayload();
	int lastTwoBytesAsInt = ByteBuffer.wrap(binaryData, binaryData.length-2, 2).getShort();
	return Integer.toString(lastTwoBytesAsInt);
}

for a formatter or

$.readShort(payload.length - 2)

for a graph value expression.

Is it possible to do what I'm trying to do? If so, how? Perhaps there is another toolset that can easily do this instead of mqtt-spy?

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