Interfacing with a 7-Segment Display using SPI and the Bus Pirate

Control a 7-segment display with the Bus Pirate through the SPI protocol to display numbers or letters.

1. Introduction

In this experiment, we’ll use the Bus Pirate to interface with a 7-segment display through the SPI protocol. This setup allows us to send specific patterns to display numbers or characters on the 7-segment display.

2. Required Components

Bus Pirate (v3.6 or later)
7-segment display with SPI driver (e.g., MAX7219 or 74HC595 shift register)
Connecting wires
Computer with terminal software (e.g., PuTTY or Tera Term)

3. Wiring Setup

Connect the 7-segment display to the Bus Pirate as follows (assuming a MAX7219 or similar driver IC):

DIN (data in) on the 7-segment driver to MOSI on the Bus Pirate
CLK (clock) on the driver to CLK on the Bus Pirate
LOAD/CS (chip select) on the driver to CS on the Bus Pirate
VCC on the 7-segment driver to an external 5V power supply or Bus Pirate’s 5V
GND on the driver to GND on the Bus Pirate

Note: If using a 74HC595 shift register instead, the wiring is similar, with SH_CP as the clock input and ST_CP as the latch.

4. Configuring the Bus Pirate for SPI

Open your terminal software and set up the Bus Pirate for SPI communication:

m 5

Select SPI mode. Configure the settings for SPI communication as follows:

3 - Set the Bus Pirate to operate at 1MHz
2 - Select idle low, clock phase setup
1 - Set the output type to normal (3.3V)
(3) - Enable power supplies (if powering through the Bus Pirate)

Your Bus Pirate is now set up to send data to the 7-segment display via SPI.

5. Sending Data to the 7-Segment Display

The 7-segment driver interprets specific hex values to display numbers and letters. Here’s a sample command sequence to send data:

[ 0x0C 0x01 ]   // Turn on the display (MAX7219)

[ 0x01 0x06 ]   // Send hex code to display the number '6'

Refer to the driver IC’s datasheet for specific commands and hex codes for displaying different characters.

6. Example: Displaying Numbers 0-9

To display the numbers 0-9 in sequence on the 7-segment display:

[ 0x01 0x3F ]  // Display '0'

[ 0x01 0x06 ]  // Display '1'

[ 0x01 0x5B ]  // Display '2'

[ 0x01 0x4F ]  // Display '3'

[ 0x01 0x66 ]  // Display '4'

[ 0x01 0x6D ]  // Display '5'

[ 0x01 0x7D ]  // Display '6'

[ 0x01 0x07 ]  // Display '7'

[ 0x01 0x7F ]  // Display '8'

[ 0x01 0x67 ]  // Display '9'

Send each command in sequence to see the numbers displayed. These hex values are typical for a common cathode 7-segment display driven by the MAX7219.

7. Troubleshooting Tips

No Display: Double-check wiring and make sure the Bus Pirate is in SPI mode.
Incorrect Characters: Verify that you’re sending the correct hex codes for your 7-segment display model.
Dim Display: Adjust the power supply voltage if the display is too dim.

8. Conclusion

Interfacing a 7-segment display with the Bus Pirate via SPI provides an excellent opportunity to explore SPI communication and control visual displays for numeric and alphanumeric output.