Documentation Index
Fetch the complete documentation index at: https://docs.zerokeyusb.com/llms.txt
Use this file to discover all available pages before exploring further.
ZeroKeyUSB uses a 0.91” SSD1306-based OLED module to present menus, credentials, and status icons. The display is bright, low-power, and readable from multiple angles — ideal for a quick glance during logins.
Electrical characteristics
| Parameter | Value |
|---|
| Resolution | 128 × 32 pixels |
| Interface | I²C (address 0x3C) |
| Supply voltage | 3.3 V |
| Typical current | 10–12 mA at full brightness |
| Controller | Solomon Systech SSD1306 |
Pin assignments
| OLED pin | Signal | Notes |
|---|
| VCC | 3V3 | Powered from the MCU regulator |
| GND | GND | Common ground |
| SCL | PA23 | Shared I²C clock |
| SDA | PA22 | Shared I²C data |
| RES | PA14 | Controlled by firmware during init |
| DC | Tied low | Command/data handled automatically in I²C mode |
| CS | Tied low | Not used in I²C mode |
Frame buffer strategy
- The SSD1306 expects data in pages of 8 vertical pixels.
- Firmware maintains a 512-byte buffer in SRAM (
128 × 32 / 8).
- Updates use partial writes to minimize I²C traffic when only a few characters change.
- A simple double-buffer diff tracks dirty regions so the screen refresh stays under 5 ms.
Animations such as smooth scrolling for long passwords rely on timer interrupts that shift the buffer between refreshes.
Brightness control
- Default contrast value:
0x7F (50%).
- Menu option allows dimming down to
0x20 for dark environments.
- After 60 seconds of inactivity the firmware sends
DISPLAY OFF while keeping data in RAM.
- Any touch input or USB activity turns the screen back on instantly.
This approach balances legibility and OLED lifespan.
Troubleshooting
| Symptom | Possible cause | Fix |
|---|
| No image, backlight off | RES pin held low | Check solder joint or ensure the boot logo finished. |
| Display flashes or shows noise | I²C conflict with EEPROM | Inspect pull-up resistors and cable length. |
| Ghosting / burn-in | Static content at max brightness | Lower contrast or enable auto-dim in settings. |
