The Raspberry Pi Zero W was announced on the fifth anniversary of the original RPi. TechRepublic has the story — Raspberry Pi Zero W: The smart person’s guide. “This comprehensive guide covers everything you need to know about the $10 Raspberry Pi Zero W, the latest tiny computer from the Raspberry Pi Foundation.”
The price is getting down to where it fades into the noise for onesy projects. There are competitors like the C.H.I.P. that promise a bit more for a bit less but these currently suffer availability and support. This is full scale modern computing getting into the price range of the microcontrollers that generally have 80’s era computing capabilities plus special hardware capabilities.
A complimentary trend is that many sensors now have internal processing to convert some physical phenomena to a measurement that can be communicated via I2C or SPI or other established protocol. The RPi is well suited for this sort of thing. The microcontrollers maintain the lead when the ADC comes into play to convert analog voltages to a digital measurement. They also lead when it comes to very low power capabilities. EEVBlog has a discussion about Everything including the Kitchen sink under $1.
Another difference is about real time response in a known time frame. This could be important in a device like the NTP Stratum 1 server based on a GPS pulse per second signal in order to assure the best possible accuracy. The small computers often run Linux which is not a real time operating system and that means that there could be some latency between a PPS signal and the computer’s doing something with it. The issues are described on the Free RTOS page. The ESP8266 is a microcontroller that uses RTOS in order to multitask its WiFi radio needs and allow other processes to get done as well. The clock rate on modern devices reduce the real time issues even though higher clock rates usually mean higher power draws. The ESP8266 runs at about 80 MHZ and the RPi at 1 GHz. Contrast that to digital audio where the highest sampling rate is under 100 KHz. Even the ESP8266 can get in 800 instructions between audio data chunks.
Memory is another factor. It determines the programming for the device and impacts power draw. The ESP8266 depends upon external memory which was a major factor in its popularity. It’s internal memory for running programs is rather limited. Most microcontrollers use internal memory and that is often well under a MB in size. The small computers need a half GB for software plus external memory that often runs into multiple GB size.
User input and output can be another issue. Microcontrollers are usually quite limited in this area as they are intended for special use devices. Computers are more generic and have more memory for user interface software. Video in this graphical interface era can be a major factor as well as it needs a lot of memory and a lot of processing capabilities.
The things you can do! That’s perhaps the biggest problem is that of trying to figure out what to do.