How to send control signal to sensor (arduino/ rasberry pi like)?

[Farmer-Ed]

I probably suggest Node-Red too often around here…
But in this case Node-Red is probably the ideal solution.

You’ve a couple of options, personally i’d send the sensor values direct to Node-Red and have it handle all of the alerts/ automation and just forward the sensor values on to farmOS.

I wouldn’t rely on e-mail notifications to control a motor if it is critical for cooling.

Edit:
I’ve done some experimenting with external notifications from farmOS in the past, take a look here:

External notifications, webhooks, MQTT etc

Any modules for 2.x in development for dispatching events to external applications? I seen this thread Controlling remote devices from within FarmOS - #5 by MBConsultingUK but presume its 1.x discussion. I’ve also tried a Drupal Webhooks module but so far have not gotten it to work. Webhooks | Drupal.org I got the following in error logs after enabling and creating a new log. Are there routing differences between Standard Drupal and farmOS? Symfony\Component\Routing\Exception\RouteNotFoundEx…

but again if it is a critical response to an over temperature event then less is definitely more, handle it directly with your microcontroller if possible or at least within one application if using GPIO on a Raspberry pi.