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STMPE821 Datasheet(PDF) 8 Page - STMicroelectronics |
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STMPE821 Datasheet(HTML) 8 Page - STMicroelectronics |
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8 / 55 page  STMPE821 functional overview STMPE821 8/55 1.4 Calibration algorithm The STMPE821 maintains 2 parameters for each TOUCH channel: TVR and CALIBRATED IMPEDANCE. CALIBRATED IMPEDANCE is an internal reference of which, if the currently measured IMPEDANCE exceeds the CALIBRATED IMPEDANCE by a magnitude of TVR, it is considered a TOUCH. If the IMPEDANCE is more than the CALIBRATED IMPEDANCE, but the magnitude does not exceed CALIBRATED IMPEDANCE by TVR, it is not considered a TOUCH. In this case, 2 scenarios are possible: 1. Environmental changes has caused the IMPEDANCE to increase 2. Finger is near the sensing pad, but not near enough In case 1, the change in IMPEDANCE is expected to be small, as environmental changes are normally gradual. A value "EVR" is maintained to specify the maximum IMPEDANCE change that is still considered an environmental change. ‘IMP’ and ‘CALIBRATED IMP’ used in this table is not the direct register read-out. IMP = 127 - impedance register read-out CALIBRATED IMP = 127 - calibrated impedance register read out. ETC WAIT register state a period of time of which, all TOUCH inputs must remain "NO TOUCH" for the next calibration to be carried out. CAL INTERVAL states the period of time between successive calibrations when there are prolonged NO TOUCH condition. Table 3. Calibration action under different scenarios Scenario Touch sensing and calibration action IMP>CALIBRATED IMP + TVR TOUCH, no calibration IMP<CALIBRATED IMP + TVR IMP>CALIBRATED IMP + EVR NO TOUCH, no calibration IMP<CALIBRATED IMP + TVR IMP<CALIBRATED IMP + EVR IMP>CALIBRATED IMP NO TOUCH, new CALIBRATED IMP = previous CALIBRATED IMP + change in IMP IMP>CALIBRATED IMP CALIBRATED IMP + change in IMP IMP<CALIBRATED IMP NO TOUCH, new CALIBRATED IMP = new IMP |
Similar Part No. - STMPE821_09 |
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Similar Description - STMPE821_09 |
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