Help with mqtt servo control

[joe_lurker]

Hi,

I'm trying to get a JSON message sent from amazon AWS to control the position of a servo.

my goal is to be able to turn a JSON like this:

into usable variables in the device like this:

i.e

I am using the AWS_IoT_WiFi example in GitHub - arduino/ArduinoCloudProviderExamples: Examples of how to connect various Arduino boards to cloud providers.

I'm wondering if anyone has had any success with getting values parsed from a json sent over mqtt and populated into usable variables. I'm using a Nano 33 IoT.

The ArduinoJson library claims to be able to do that, but I feel that I am not grasping the concepts well enough to apply it correctly.

I am able to read the contents of the message using:

but I would like to be able to expand on this and parse the JSON to extract the information, but I'm stuck.

I think I'm having conversion trouble. If there is an easier way of doing this please let me know. I'm open for options.

[jjo998]

I'm probably not the best person to help with this, but I'm currently working on a project that filters MQTT messages.

Can you put the message you are getting form the serial monitor when an MQTT comes in?

[joe_lurker]

Hi, thanks for getting back to me.

This is what I get when I send that test JSON from AWS.

And this is the function that is called when the MQTT comes in.

...as expected.

The issue I have is when I'm trying to implement the ArduinoJson.h:

There's something in my understanding that I'm missing. I tried to effectively replicate what was in one of the examples but it doesn't seem to be compatible with what I am trying to do.

In the example, they 'provide' the json[] for it to deserialise.... You can see how I've tried to replace the json in the example with (char)mqttClient.read(); and hoped it would work(?). I think I need to understand what I'm missing and why that can't be done.