Raspberry Pi Pico-Based System Identification

This project uses a Raspberry Pi Pico to identify and store various information about a system/fixture, settable and retrievable over UART or USB. Additionally, writing can be disabled by jumping GPIO pins 14 and 15 together (pins 19 and 20 on the board), and GPIO 13 (pin 17 on the board) can be switched to GND and used as a pulse counter, such as for a fixture lid switch. This pin is active low and counts any low pulse longer than a minimum time period (configurable by with a CMake variable).

This project makes use of a Pi Pico and a MIKROE EEPROM 3 Click. The I2C lines for the EEPROM should be connected to GPIOs 16 (SDA) and 17 (SCL) (pins 21 and 22 on the board, respectively).

Pre-build UF2 binaries are available for USB or UART configurations here.

Important

This is the new version with pulse counting using the AT24CM02 I2C EEPROM chip. For the old version without pulse counting which uses only the Pico's on-board flash, use version 1.3.0.

Information Fields

There are 10 R/W information fields stored on the device. It's also possible to read the Pico's unique 64-bit identifier as a hex string, but of course this is read-only. The idea is that the Pico's serial number can always be used to uniquely identify any device, as no two Picos have the same serial.

The EEPROM specifies up to 1,000,000 writes per flash cell (per 4-byte word). Using a simple wear-leveling scheme using 16 words, the theoretical minimum number of pulses that can be counted without resetting is about 16 million. This is expected to be incredibly high for most applications, but by changing a constant, this number can be trivially increased for more demanding applications.

Field	Access	Description
MFG	Read-write	Manufacturer
NAME	Read-write	Name
VER	Read-write	Version
DATE	Read-write	Date
PART	Read-write	Part number
MFGSERIAL	Read-write	Manufacturer's custom serial number
USER1	Read-write	General-purpose field 1
USER2	Read-write	General-purpose field 2
USER3	Read-write	General-purpose field 3
USER4	Read-write	General-purpose field 4
SERIAL	Read-only	Pico's unique 64-bit serial number
PULSECOUNT?	Read-only	Low pulse count on GP13 (board pin 17)

Note that each of the above fields has a maximum length of 63. Each field is 64 bytes, but is null-terminated. Values longer than 63 bytes will be truncated.

Commands

Communicating with the Pico over serial is very simple. Each command must be terminated with a carriage return (\r). If a line feed (\n) is sent afterwards, it will be ignored. Use 115200 baud, no flow control, 8 bits per byte, 1 stop bit.

To set a field, send the field name, an equals sign, and the field's value. For example, to set the device's manufacturer field:

MFG=Bloomy Controls\r

To query a value, send the name of the field followed by a question mark. The Pico will respond with the value delimited by a CRLF (\r\n). For example, to query the manufacturer:

MFG?\r

There are some additional commands:

Command	Description
CLEAR	Clear all writable fields
CHECK?	Check that the data stored in EEPROM matches the stored checksum, then return either OK or ERR
RESETCOUNT	Reset the pulse count to 0

Build Requirements

You'll need Ubuntu or Debian to build this (WSL works just fine). Before attempting to build this project, install required packages using the following commands:

sudo apt update
sudo apt upgrade
sudo apt install cmake gcc-arm-none-eabi libnewlib-arm-none-eabi build-essential python3 git

Building

First, you must configure the build system:

cmake -B build

This step may take quite some time, as it will download the Pi Pico SDK. If you wish to use USB for serial communications instead of UART, add -DUSB_SERIAL=ON to the above command.

The default minimum pulse width is 100ms. To override this time limit, pass -DMIN_PULSE_WIDTH_US=500000 to get 500ms (you can use any whole number of microseconds greater than or equal to 50,000).

After the configuration step is done, you can build the project like so:

cmake --build build

This will generate all the outputs in the build directory. The UF2 file (used to flash the Pico) will be named pico-ident.uf2.

Installing

To install the firmware onto the pico, hold down the BOOTSEL button on the Pico while you are plugging in its USB cable. It should show up as a storage device in your file explorer. Simply drag and drop the UF2 file to it and it should unmount automatically. It's now flashed and ready to use.