The Raspberry Pi (Raspi) is a single board computer that utilises an ARM based SOC that has all the attributes of a microcontroller but with greater system resources. Raspi is based on a processor chip that has been widely used in smartphones and in common with 'smart' devices runs a high level operating system In the Raspi case this is Linux. The Raspi sytem provides a number of Input/Output pins refered to as GPIO pins, USB ports, LAN port, video HDMI output, audio output and on the later models built-in WIFI connectivity. The Linux variant used is Raspbian and is derived from a Debian base. There are other operating systems available i.e. Ubuntu to name one. Both Raspbian and Ubuntu have graphic frontends but as my projects do not require a screen display the Raspi is run 'headless', no screen, keyboard or mouse.
The original Raspi used a single core processor chip and later devices use a quad core processor, either chip is more than capable of running multiple tasks, quad core variants can run more time critical programs. There are no time critical elements to the logger project and even on a single core machine there is plenty of spare processing power to do other tasks. The system pictured on the webpages also runs a local web server as well as acting as a host to receive files from security cameras. These pictures are initially produced by a network connected camera, they become part of a locally hosted website on the Raspi that transfers the picture files to this website.

The Raspi running Linux is the ideal solution for connecting a project to the internet, either for control or data display. Only software is required and there are a lot of Linux application available plus the built-in utilities.

Although it is possible to directly interface to the Raspi I/O pins they are 3v3 logic level and directly connect to the processor chip. I do not like having wiring in the wider world (i.e. outside of the equipment case) connecting directly to the processor chip and so use a PIC microcontroller as the frontend to the world outside of the case.

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