How to design a "Smart Device"?

The process is the same for any "smart device" development and based on the common principle of "measure some parameters via sensors or transducers - do some maths on the values measured - then initiate some designed for action in response". The cycle then repeats itself continuously. How easy is that?

In another form a "smart device" can be one that uses feedback from inputs to build up enough semi intelligence to operate in a feed forward state of mind. Let me explain this point more. There are two ways to monitor the state of wear of a bearing for example, we can constantly measure its vibration signature and respond in some way OR we may choose to ignore actually measuring its vibration characteristics but instead use some other pieces of information available about the bearing and its operating circumstances and from that data we can draw an "inference" as to the health of the bearing. This is called "inferential measuring/monitoring" and it will become an important principle for you to come to terms with as you go forward.

I utilize inferential monitoring in defining and controlling our micro grid renewable energy systems operations; such as PV Solar; Hydro and Wind, and have been doing so with "smart devices" [all having various degrees of semi intelligence] for over 40 years - well before computers.

The equivalent "smart devices" of the day resolved sensors and transducers inputs into mechanical "servo mechanism" outputs very effectively, inferential control was quite difficult to accommodate in the early days though. Today it’s a walk in the park.

To summarize: Be precise in defining what it is that you want to measure and the format of your array of measuring sensors/transducers. Define the math to be done on the measurements.

You need to be strong on complex Boolean logic to do a good job. Initiate the desired action/s responses, and ensure that you have an accurate feedback loop in place to report the state of any actions taken. Consider "dependencies" carefully. In other words, what happens to "A" if this happens to "B"?

Finally learn about hysteresis and the concept of dither mechanisms which may come in handy depending on your location and operating circumstances.