Lighting a Single-Digit 7-Segment Display (Common-Cathode) on a Raspberry Pi 4B

Step by step

1. Drag Raspberry Pi 4B onto the Canvas.
2. Drag the Single-Digit 7-Segment Display onto the Canvas — a real 10-pin DIP package. It mounts straight into a breadboard spanning the center gap, the same way the MCP3008 does, or wires directly to the Pi.
3. Hover its pins to confirm the labels. Bottom edge, left to right: E, D, COM, C, DP. Top edge, left to right: G, F, COM, A, B — the two COM pins sit in the same column, on opposite edges, and are internally tied together (wiring GND to either one grounds both).

4. Wire either COM pin → a Pi GND pin — this is the shared cathode for all 8 segments.
5. Wire each of the 8 segment pins (A-G, DP) → its own Resistor → its own Pi GPIO pin, exactly the same series-resistor treatment a plain LED needs. Each segment is electrically independent — there's no shared anode, so any combination can light at once.
6. Go to the Code tab and write a script that lights an arbitrary pattern — not a real digit:

import RPi.GPIO as GPIO
import asyncio
 
GPIO.setmode(GPIO.BOARD)
# adjust these to match your wiring
SEG_A, SEG_C, SEG_F, SEG_DP = 37, 38, 40, 36
 
for pin in (SEG_A, SEG_C, SEG_F, SEG_DP):
    GPIO.setup(pin, GPIO.OUT)
 
while True:
    GPIO.output(SEG_A, GPIO.HIGH)
    GPIO.output(SEG_C, GPIO.HIGH)
    GPIO.output(SEG_F, GPIO.HIGH)
    GPIO.output(SEG_DP, GPIO.HIGH)
    print("A + C + F + DP lit — not a real digit shape")
    await asyncio.sleep(2)
 
    GPIO.output(SEG_A, GPIO.LOW)
    GPIO.output(SEG_C, GPIO.LOW)
    GPIO.output(SEG_F, GPIO.LOW)
    GPIO.output(SEG_DP, GPIO.LOW)
    await asyncio.sleep(2)

7. Click Start.

There's deliberately no digit-lookup table anywhere in this simulator — each segment reacts purely to its own pin's HIGH/LOW state, the same way 8 completely independent LEDs would. That's exactly what makes this component ready to pair with a 74HC595 shift register later: the shift register just drives each of these 8 pins bit-by-bit, and the display doesn't need to know or care what "digit" that pattern happens to represent.

What “working correctly” looks like

• Each segment lights independently the instant its own pin goes HIGH — driving only A and G, for example, lights just those two strokes, not a recognizable digit.
• Wiring GND to only ONE of the two COM pins still correctly grounds every segment — the two commons are internally tied together on this component, matching the real hardware (they're the same physical node, split into two pins purely for the package's own mechanical layout).
• A resistor value that's too low logs the same low-series-resistance advisory a plain LED gets, scoped to whichever lit segment currently has the least series resistance.
• The reference script above lights A, C, F, and DP together — a pattern that doesn't correspond to any real digit — confirming there's no hidden digit lookup silently "correcting" your wiring.

If something’s wrong

• A segment never lights → confirm that segment's own pin is wired through a resistor to a Pi GPIO pin your script actually drives HIGH, and confirm at least one COM pin reaches a real Pi GND pin.
• One segment stays permanently dim or dark while others work → check that segment's own resistor value; a disconnected or extremely high-value resistor starves that one segment of current.
• You expected a real digit shape and got something else → this component has no digit-to-segment lookup at all; double-check which physical segment (A-G, DP) each of your wires actually lands on, using the pin table above.