Os motores de busca de Datasheet de Componentes eletrônicos |
|
AD7142 Folha de dados(PDF) 18 Page - Analog Devices |
|
AD7142 Folha de dados(HTML) 18 Page - Analog Devices |
18 / 70 page AD7142 Data Sheet Rev. B | Page 18 of 70 NONCONTACT PROXIMITY DETECTION The AD7142 internal signal processing continuously monitors all capacitance sensors for noncontact proximity detection. This feature provides the ability to detect when a user is approaching a sensor, at which time all internal calibration is immediately disabled and the AD7142 is automatically configured to detect a valid contact. The proximity control register bits are described in Table 12. The FP_PROXIMITY_CNT register bits and LP_PROXIMITY_CNT register bits control the length of the calibration disable period after the user leaves the sensor and proximity is no longer active, in full and low power modes. The calibration is disabled during this time and enabled again at the end of this period provided that the user is no longer approaching, or in contact with, the sensor. Figure 28 and Figure 29 show examples of how these registers are used to set the full and low power mode calibration disable periods. Calibration disable period in full power mode = FP_PROXIMITY_CNT × 16 × Time taken for one conversion sequence in full power mode Calibration disable period in low power mode = LP_PROXIMITY_CNT × 4 × Time taken for one conversion sequence in low power mode RECALIBRATION In certain situations, the proximity flag can be set for a long period, for example when a user hovers over a sensor for a long time. The environmental calibration on the AD7142 is suspended when proximity is detected, but changes may occur to the ambient capacitance level during the proximity event. This means the ambient value stored on the AD7142 no longer represents the actual ambient value. In this case, even when the user has left the sensor, the proximity flag may still be set. This situation could occur if the user interaction creates some moisture on the sensor causing the new sensor ambient value to be different from the expected value. In this situation, the AD7142 automatically forces a recalibration internally. This ensures that the ambient values are recalibrated regardless of how long the user hovers over a sensor. A recalibration ensures maximum AD7142 sensor performance. The AD7142 recalibrates automatically when the measured CDC value exceeds the stored ambient value by an amount determined by PROXIMITY_RECAL_LVL, for a set period of time known as the recalibration timeout. In full power mode, the recalibration timeout is controlled by FP_PROXIMITY_RECAL, and in low power mode, by LP_PROXIMITY_RECAL. Recalibration timeout in full power mode = FP_PROXIMITY_RECAL × Time taken for one conversion sequence in full power mode Recalibration timeout in low power mode = LP_PROXIMITY_RECAL × Time taken for one conversion sequence in low power mode Figure 30 and Figure 31 show examples of how the FP_PROXIMITY_RECAL and LP_PROXIMITY_RECAL register bits control the timeout period before a recalibration, operating in the full and low power modes. These figures show a user approaching a sensor followed by the user leaving the sensor and the proximity detection remains active after the user leaves the sensor. The measured CDC value exceeds the stored ambient value by the amount set in the PROXIMITY_RECAL_LVL bits, for the entire timeout period. The sensor is automatically recalibrated at the end of the timeout period. The forced recalibration takes two interrupt cycles, therefore, do not set it again during this interval. PROXIMITY SENSITIVITY The fast filter in Figure 32 is used to detect when someone is close to the sensor (proximity). Two conditions set the internal proximity detection signal using Comparator 1 and Comparator 2. Comparator 1 detects when a user is approaching a sensor. The PROXIMITY_DETECTION_RATE register controls the sensitivity of Comparator 1. For example, if PROXIMITY_DETECTION_RATE is set to 4, the Proximity 1 signal is set when the absolute difference between WORD1 and WORD3 exceeds four LSB codes. Comparator 2 detects when a user hovers over a sensor or approaches a sensor very slowly. The PROXIMITY_RECAL_LVL register (Address 0x003) controls the sensitivity of Comparator 2. For example, if PROXIMITY_RECAL_LVL is set to 75, the Proximity 2 signal is set when the absolute difference between the fast filter average value and the ambient value exceeds 75 LSB codes. Table 12. Proximity Control Registers (See Figure 32) Register Length Register Address Description FP_PROXIMITY_CNT 4 bits 0x002 [7:4] Calibration disable time in full power mode LP_PROXIMITY_CNT 4 bits 0x002 [11:8] Calibration disable time in low power mode FP_PROXIMITY_RECAL 8 bits 0x004 [9:0] Full power mode proximity recalibration time LP_PROXIMITY_RECAL 6 bits 0x004 [15:10] Low power mode proximity recalibration time PROXIMITY_RECAL_LVL 8 bits 0x003 [13:8] Proximity recalibration level PROXIMITY_DETECTION_RATE 6 bits 0x003 [7:0] Proximity detection rate |
Nº de peça semelhante - AD7142_17 |
|
Descrição semelhante - AD7142_17 |
|
|
Ligação URL |
Privacy Policy |
ALLDATASHEETPT.COM |
ALLDATASHEET é útil para você? [ DONATE ] |
Sobre Alldatasheet | Publicidade | Contato conosco | Privacy Policy | roca de Link | Lista de Fabricantes All Rights Reserved©Alldatasheet.com |
Russian : Alldatasheetru.com | Korean : Alldatasheet.co.kr | Spanish : Alldatasheet.es | French : Alldatasheet.fr | Italian : Alldatasheetit.com Portuguese : Alldatasheetpt.com | Polish : Alldatasheet.pl | Vietnamese : Alldatasheet.vn Indian : Alldatasheet.in | Mexican : Alldatasheet.com.mx | British : Alldatasheet.co.uk | New Zealand : Alldatasheet.co.nz |
Family Site : ic2ic.com |
icmetro.com |