How do I write to a ThingSpeak channel from a Raspberry pi via code deployed using the Matlab Coder?

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John Anderson on 19 Jun 2019

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Commented: John Anderson on 24 Nov 2020

I am making use of the Matlab Coder to deploy Matlab functionality to a Raspberry pi. I would like to be able to deploy the ability to write to a ThingSpeak channel from the pi. I realise that this is possible using Simulink (via the ThingSpeak block) but was wondering if there is a simple way to do this via code deployed using the Matlab Coder. I have tried the obvious and found that the Matlab Coder does not recognise the ThingSpeakWrite command. However, it also doesn’t appear to be very straightforward to deploy http methods to enable updating the channel via the POST method. Any advice welcome.

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John Anderson on 21 Jun 2019

Using curl via the system command deploys via the coder without any problems. Not sure if it the most sensible way but does enable updating of a thingSpeak channel and is very easy to implement. Example code below adds random number to field 1 of channel.

% raspberry pi object
r = raspi();
% log file
fid = fopen( 'logFile.log', 'w' );
% write random number to thingSpeak channel
v = rand;
commandStr =  [ 'sudo curl  -s "https://api.thingspeak.com/update.json?api_key=<your api key here>&field1=' sprintf( '%f', v ) '"' ];
result = system( r, commandStr );
% log command
fprintf( fid, '%s \n', commandStr );
% log result
fprintf( fid, '%s \n', result );
% close log
fclose( fid );