HP1345A Vector Display Driver (ESP32-S3)

Drive an HP 1345A vector display in immediate mode from a Heltec WiFi Kit 32 V3 (ESP32‑S3). This project bit‑bangs the 15‑bit data bus and handshake lines, renders a set of vector test patterns, and shows status on the onboard OLED.

What this is for

• Bring up the HP1345A immediate‑mode interface (D0–D14 + DAV/RFD).
• Exercise the vector display with multiple geometric test patterns.
• Provide a small OLED status panel (connected/disconnected).

Hardware you need

• HP 1345A vector display (immediate mode).
• Heltec WiFi Kit 32 V3 (ESP32‑S3).
• Resistor divider for RFD (5V -> 3.3V).
• Common ground between HP and ESP32.
• Optional: scope or DMM for wiring verification.

Wiring

The HP1345A immediate‑mode bus uses D0–D14 (15 bits). D15 and the Option‑704 lines (DS/RD/XACK/SYNC) are not used.

Data bus (HP → ESP32)

HP Signal	ESP32 GPIO
D0	GPIO1
D1	GPIO2
D2	GPIO3
D3	GPIO4
D4	GPIO5
D5	GPIO6
D6	GPIO7
D7	GPIO39
D8	GPIO40
D9	GPIO41
D10	GPIO42
D11	GPIO37
D12	GPIO33
D13	GPIO47
D14	GPIO48

Control lines

HP Signal	ESP32 GPIO	Direction
DAV (active‑low)	GPIO20	OUT
RFD (active‑low)	GPIO19	IN
DISCONNECT SENSE	GND	tie to ground
GND	GND	common ground

RFD level shifting (required)

HP RFD is 5V TTL. Do not connect directly to ESP32.

Suggested divider:

HP RFD ---- 10k ----+---- ESP32 GPIO19
                   |
                  20k
                   |
                  GND

OLED (onboard)

The code uses the onboard 0.96" OLED (SSD1306 class) via I2C:

• SDA = GPIO17
• SCL = GPIO18
• RST = GPIO21
• Vext = GPIO36 (active‑low enable)

If your board revision differs, set SCREEN_SDA, SCREEN_SCL, SCREEN_ADDR, SCREEN_RST_PIN, or SCREEN_VEXT_PIN via build flags.

Build & flash (PlatformIO)

1. Install PlatformIO (VSCode or CLI).
2. Connect the ESP32 board.
3. Build/flash:

   pio run -t upload
   

4. Monitor serial output:

   pio device monitor
   

Serial runs at 115200.

Serial commands

Type into the serial monitor:

• h help
• s status
• d pulse DAV low (wiring check)
• w toggle D11 (pen bit) for wiring check
• p toggle pen up/down sense
• t toggle transfers on/off
• v toggle verbose logging
• b toggle per‑word handshake trace
• x toggle RX echo
• 0..9 select test pattern
• n next test pattern

Test patterns

There are multiple test cases (0–9). Examples include:

• Geometric primitives (square, spiral, circle)
• Starburst
• Ripple/sombrero mesh (cached for speed)
• Spirograph
• Checkerboard
• Starfield and Matrix‑style text

The top‑left text overlay shows FPS and V (vectors per frame).

Troubleshooting

RFD never goes low

• Ensure DAV is high (idle).
• Check DISCONNECT SENSE is tied to HP ground.
• Confirm your RFD divider wiring and common ground.

No display / blank

• Verify correct data bus wiring.
• Use the d command to pulse DAV and check at HP pin 10 with a scope.
• Try toggling the pen bit with w and probe D11.

OLED blank

• Confirm Vext (GPIO36) is driven LOW.
• Check SDA/SCL pins and address (0x3C/0x3D).

Project layout

src/
  main.cpp              // Test patterns, loop, serial UI
  hp_vector_device.*    // HP1345A immediate‑mode bus + handshake
  screen.*              // OLED wrapper (Adafruit GFX / SSD1306)
platformio.ini

Safety notes

The HP1345A contains high voltages. Do not open or service it while powered. Always power down before rewiring.