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NanoVNA-H NanoVNA-H Documentation

Touch Calibration

The NanoVNA-H touchscreen requires calibration to ensure accurate tap detection. This is especially important after replacing the screen or if touch inputs seem offset.

When to Calibrate

Section titled “When to Calibrate”

Touchscreen calibration is needed when:

  • Touch responses are offset from tap location
  • Menus are difficult to select
  • After replacing the display
  • After a firmware reset

Start Touch Calibration

Section titled “Start Touch Calibration”

Via Menu

Section titled “Via Menu”
  1. Tap the screen to open the menu
  2. Navigate to CONFIG
  3. Tap TOUCH CAL
  4. Follow the on-screen prompts

Via Shell Command

Section titled “Via Shell Command”
Terminal window
touchcal

This starts the calibration process immediately.

Calibration Process

Section titled “Calibration Process”
  1. A crosshair appears at the top-left corner
  2. Tap precisely on the center of the crosshair
  3. A crosshair appears at the bottom-right corner
  4. Tap precisely on the center of this crosshair
  5. Calibration completes automatically

After Calibration

Section titled “After Calibration”

After successful calibration:

  1. The device returns to normal operation
  2. Test by tapping different areas of the screen
  3. If still inaccurate, repeat calibration
  4. Save configuration with saveconfig to preserve settings

Save Calibration

Section titled “Save Calibration”

Touch calibration data is stored in the configuration. To preserve it across power cycles:

Terminal window
saveconfig

Or via menu: CONFIG > SAVE

Test Touch Accuracy

Section titled “Test Touch Accuracy”

After calibration, verify accuracy:

Via Menu

Section titled “Via Menu”

Navigate through menus and verify:

  • Menu items respond to direct taps
  • Marker placement works correctly
  • Keypad buttons are responsive

Via Shell Command

Section titled “Via Shell Command”
Terminal window
touchtest

This enters a test mode showing raw touch coordinates. Touch different areas and verify the coordinates match the tap location.

To exit touch test: tap rapidly or use the shell to send a command.

Shell Commands

Section titled “Shell Commands”
Terminal window
# Start touch calibration
touchcal


# Test touch coordinates
touchtest

Calibration Data

Section titled “Calibration Data”

Touch calibration uses two reference points to calculate:

  • X and Y offset
  • X and Y scaling factors

The calibration compensates for:

  • Panel alignment tolerances
  • Mounting variations
  • Touch controller offsets

Troubleshooting

Section titled “Troubleshooting”

Calibration Won’t Start

Section titled “Calibration Won’t Start”
  • Ensure the device isn’t in sweep mode (pause first)
  • Try using the shell command touchcal
  • Restart the device and try again

Calibration Seems Wrong After Completion

Section titled “Calibration Seems Wrong After Completion”
  • Repeat calibration with more careful taps
  • Use a stylus for precision
  • Ensure you tap the exact center of crosshairs

Touch Still Inaccurate

Section titled “Touch Still Inaccurate”
  • Clean the screen surface
  • Check for screen protector interference
  • Verify display is properly seated
  • Try multiple calibration attempts

After Replacing Screen

Section titled “After Replacing Screen”

New screens may have different touch characteristics:

  1. Install new screen
  2. Power on device
  3. Immediately run touch calibration
  4. Save configuration

Default Calibration

Section titled “Default Calibration”

If the touch becomes unusable and you cannot navigate menus:

  1. Connect via USB
  2. Open serial console
  3. Run touchcal command
  4. Complete calibration using on-screen crosshairs
  5. Run saveconfig to save

Technical Details

Section titled “Technical Details”

The touch calibration stores:

  • _touch_cal[0]: X offset
  • _touch_cal[1]: Y offset
  • _touch_cal[2]: X scale factor
  • _touch_cal[3]: Y scale factor

These values transform raw touch ADC values to screen coordinates.