INTRODUCTION: The purpose of this project is to create a custom platform for developing with a PIC Microcontroller. The intent is to create a system useful for teaching students about embedded systems, and the PIC architecture in particular. For this reason, it is designed to be easy to make, easy to use, and to have enough support that someone with little prior knowledge would be able to make use of it.
The intended end users, students with little experience with embedded systems, dictated the requirements of the project. A student that had never seen a soldering iron should be able to, with some instruction, assemble the entire board by hand. This meant that components would have to be through-hole, or be of a larger surface-mounted type.
There needed to be a minimum amount of power regulation on the board, and any usable pins of the microcontroller needed to be broken out to a header compatible with a standard breadboard. Finally, the board should also include other peripherals that might be useful to a student or developer.
A very few microcontrollers in the PIC family exist that are 32-bits and available in a through-hole package. A PIC32MX250F128 was selected, having the largest memory of matching devices. Given that this device has USB functionality, one of the first additions made was a USB port. Other additions were based upon a comparison to the ATmega development board already in use. The PIC microcontroller selected only had half of the available pins of the ATmega, so one addition made was an IO Expander to add more.
Another thing that the PIC lacked was a section of nonvolatile data memory, so a suitable EEPROM chip was selected. To minimize the loss of pins, both of these were selected to use an I2C interface, resulting in a total of 2 pins given up. A set of switches was also added to allow users to connect or disconnect these peripherals. A final addition was made of an LED light, which can often be used to verify that a system is running.
With the schematic design finished, a layout was prepared. Components were placed to make them easy to solder, keeping distances between relatively large. Best practices were followed as much as possible to keep the noise in the layout minimal. The entire layout was made to fit on a board 2” wide by 3” long, and then it was verified and
sent out for manufacturing.
Once the board came back, it was populated and tested for proper operation. A minimal amount of code was written to test out functions of the microcontroller and its peripherals. Issues were identified and corrected, and the board took its final form.