Poor man's Bus Pirate

A very basic bus sniffer and communicator (UART, SPI, I2C, etc). A simplified (and cheaper) version of the Bus Pirate.

Features

This circuit can be used to either sniff communication between components (such as microcontrollers), or to directly communicate with the components using the computer.

• Supported input/output formats: ASCII, hexadecimal, decimal and binary
• Supported protocols:
  • UART (with or without hardware flow control)
    • Baud autodetect
  • SPI (master, slave, sniffing)
  • I2C (not implemented yet)
  • PWM output
• Supported I/O voltages: 3.3V and 5V

Commands

Connect the Pico USB to the computer, and then open a serial terminal to the USB port at 115200 baud.

• General
  • use [ uart | spi_master | spi_slave | spi_sniff | pwm ]
  • reset (reset all options to default)
  • set (print all variables)
• UART
  • set uart.baud [NNN] (default: 115200)
  • set uart.mode [MMM] (default: 8N1)
  • set uart.hflow [on | off] (default: off)
  • set uart.output [ascii | dec | bin | hex] (default: ascii)
  • use uart guess: tries to autodetect baudrate
• SPI
  • set spi.cpol [0 | 1] (default: 0)
  • set spi.cpha [0 | 1] (default: 0)
  • set spi.order [lsb | msb] (default: msb)
  • set spi.baud [NNNN] (baud rate in Hz, master only, default: 100000)
  • set spi.autorespond [off | NN] (always respond with byte NN, default off)
  • set spi.output [ascii | dec | bin | hex] (default: hex)
• I2C
  • set i2c.baud [NNNN] (baud rate in Hz, master only, default: 100000)
  • set i2c.output [ascii | dec | bin | hex] (default: hex)
  • use i2c scan: scan for connected slave addresses
• PWM
  • set pwm.freq [NNNN] (frequency in Hz, default: 100000)
  • set pwm.duty [NN] (% duty cycle, default: 50)

Press CTRL+C to end communication with a protocol at any time.

Settings are saved on flash, and persist after a reboot.

Communication example:

Pinout

BP pin	UART	SPI master	SPI slave	SPI sniff	I2C function	PWM function	RPi Pico pin
COMM0	TX	MISO	MOSI	RX0	SDA	PWM0	GP0 (1)
COMM1	RX0	CS	SS	SS	SCL		GP1 (2)
COMM2	CTS	SCK	SCK	SCK			GP2 (4), GP10 (14)
COMM3	RTS	MOSI	MISO				GP3 (5)
COMM4	RX1			RX1			GP5 (7), GP8 (11)
GND							GND

Circuit

This section is mandatory - it provides the computer interface, and allows communicating with components at 3.3V.

This section is optional, and allows for communicating with 5V devices as well.

This section is optional, and adds blinking lights to communication channels to indicate activity.

Firmware update

To update the firmware:

1. Download the file poor-man-bus-pirate.zip and uncompress it.
2. Connect the Raspberry Pi Pico via USB to the computer while pressing the BOOTSEL button.
3. This will create a USB mount. Copy the file poor-man-bus-pirate.uf2 into that directory.
4. Restart the Pico.

Implementation

This is the circuit I implemented for my personal use: