Skip to main content
ZeroKeyUSB replaces mechanical buttons with five copper touch pads connected to a dedicated TS06 capacitive controller. The firmware polls this controller over I²C and translates touches into navigation events.

​
Hardware overview

The controller handles baseline calibration internally and reports which channels are active via the status register.

​
Touch initialization

At startup (zerokey-setup.cpp), the firmware:
  1. Probes the TS06 at 0x69 with up to 5 retries (20 ms apart).
  2. If detected, writes minimum sensitivity (0x3F) to registers 0x00–0x02.
  3. Configures operation mode via registers 0x05–0x06.
  4. Sets ts06_ok = true — if the controller isn’t found, touch is disabled and the serial log shows "TS06 not found on I2C".

​
Polling cycle

The handleButtonChecker() method runs in the main loop:
  1. Reads STATUS_REGISTER (0x25) via readRegister() over I²C.
  2. For each channel bit:
    • Records pressStartTime when a channel first becomes active.
    • Applies a 80 ms debounce (DEBOUNCE_MS) — releases shorter than this are ignored.
    • Enforces a 150 ms channel lockout (CHANNEL_LOCKOUT_MS) — touching a different pad while one is active is ignored.
  3. On release:
    • If held > LONG_PRESS_THRESHOLD (800 ms) → dispatches long-press handler.
    • Otherwise → dispatches short-press handler.

​
Gesture mapping

​
Long-press visual feedback

When a long press is in progress, drawLongPressProgress() renders a filling progress bar on the OLED screen. This gives the user visual confirmation that they should keep holding. Releasing before 800 ms cancels the action.

​
PIN screen controls

On the PIN entry screen, the controls change:

​
Error handling

  • If the TS06 is not detected at boot, ts06_ok is set to false and the status register read returns 0x00 — effectively disabling touch input.
  • The firmware does not show a touch error screen; instead, the serial log reports the issue for debugging.
  • Touch is silently disabled during lockout delays (waitFromEeprom()) and during long-running operations like credential erasure.
The TS06 operates independently of EEPROM or ATECC608A operations. Since all share the same I²C bus at 100 kHz, touch polling is interleaved with other I²C traffic in the cooperative main loop.