Guide to Interpret CC Calibration Value

This page provides information on computing sensor capacitance values using the Compensation Capacitor (CC) value. The CC value is also called CC calibration value as it is computed during the calibration phase. The CC value of each touch button can be obtained as follows:

uint16_t cc_value = ptc_qtlib_node_stat1[SENSOR_NUMBER].node_comp_caps;

The unsigned 16-bit CC values are stored as node_comp_caps in PTC CC Register format.

PTC CC Register Format

Depending on the device, the CC register format changes.

For SAME54/SAME53/SAME51/SAMD51/SAMD20/SAMD21/SAMDA1/SAMD10/SAMD11/ATmega328PB/ATmega324PB

cc-register.png

For ATtiny81x/ATtiny161x - Self-Capacitance

cc-register-tinyself.png

For ATtiny81x/ATtiny161x - Mutual Capacitance

cc-register-tinymutual.png

CC Register Bit Values

Coarse/Fine/Accurate Bit Values

coarse-fine-accure.png

Rough Bit Values

rough.png

Computing Sensor Capacitance

For SAME54/SAME53/SAME51/SAMD51/SAMD20/SAMD21/SAMDA1/SAMD10/SAMD11/ATmega328PB/ATmega324PB

  • Read CC value in decimal: 11639
  • Read CC value in hexadecimal: 0x2D77
  • Substitute the rough, coarse, fine and accurate values from the table.
    • Rough = 13.45
    • Coarse = 8.7425
    • Fine = 0.47075
    • Accurate = 0.047075

Sensor Capacitance (pF) = Rough + Coarse + Fine + Accurate = 22.79 pF (maximum 32 pF)

For ATtiny81x/ATtiny161x - Self-Capacitance

  • Read CC value in decimal: 46967
  • Read CC value in hexadecimal: 0xB777
  • Substitute the rough, coarse, fine and accurate values from the table.
    • Rough1 = 20.175
    • Rough2 = 13.245
    • Coarse = 4.7075
    • Fine = 0.47075
    • Accurate = 0.047075

Sensor Capacitance (pF) = Rough + Coarse + Fine + Accurate = 38.99 pF (maximum 48 pF)

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