Application Note LT-1PA01. LT Series LT-1PA01. Proximity /Ambient Light Sensor. Features. Applications. Overview

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Phillip Manning
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Proximity /Ambient Light Sensor LT Series Features Proximity sensor and ambient light sensor in 1package Very small package size(l3.05 x W2.1 x H1.

1 Proximity /Ambient Light Sensor LT Series Features Proximity sensor and ambient light sensor in 1package Very small package size(l3.05 x W2.1 x H1.0 mm) Low Current consumption 80mA typical at sleeping time 800ms I2C serial communication <Proximity sensor> Extremely low current consumption Fully calibrated to 70 mm detection with gray card <Ambient Light Sensing (ALS)> Illuminance sensing angle is +/-45 degrees at 50% Low lux Performance at lux (High : 2k lux) Applications Mobile devices: Smart phone, PDA, GPS Computing devices: Laptop PC, Tablet PC Consumer devices: LCD-TV, digital picture frame, digital camera Industrial and proximity sensing Overview is an infrared proximity and ambient light sensor. In proximity sensing (PROX), the sensor can reliably detect an object entering or exiting a specified proximity field by emitting infrared light and measuring reflection from an object. In ambient light sensing (ALS), it measures the ambient light intensity. The can initiate measurements through an autonomous process. The operation procedure is described in this application note. 1 / 17

2 TABLE OF CONTENT 1. Overview 1 2. Basic Operation Initializing process 2.2 Interrupt handling Clear interrupt Read measurement data Signal processing Calculating equation of illuminance Proximity determination method 3. Sample code 10 2 / 17

3 2. Basic Operation The host can place the in an autonomous operational state where it performs measurements at set intervals and interrupts the host by asserting INT pin when measured value is greater or lesser than the preset threshold value. The can interrupt the host after each measurement is completed. When receiving the interrupt signal at INT pin, the host side read the measured value and switches the sensitivity range if necessary. Figure 2-1 shows the sequence diagrams of the host side and. Figure 2-2 shows the host side flowchart. Figure 2-1 and Figure 2-2 describe initializing process and interrupt handling. Host side Initializing process Brownout check initialization Interrupt setting PROX back-scatter setting ALS sensitivity range setting PROX sleeping time setting ALS IR Compensation setting Start measurement Interrupt handling Assert INT pin Clear interrupt source Read measurement data Figure 2-1 Sequence Diagram 3 / 17

4 Initializing process Interrupt handling Brownout check initialization Interrupt setting Is INT pin asserted? NO PROX back-scatter setting ALS sensitivity range setting YES Clear interrupt source PROX sleeping time setting Read measurement data ALS IR Compensation setting Signal processing Start measurement End End Figure 2-2 Host side processing flowchart 4 / 17

5 2.1 Initializing process In order to initialize, the host writes the setting values to register. The Table shows the register names and the corresponding setting values which make up the initializing process. Interrupt settings in the table are designed in order that the interrupt occurs on every measurement. Therefore PROX interrupt scheme is set to a window comparator scheme and PROX low threshold is set to the maximum (255) and PROX high threshold is set to the minimum (0). As a result, PROX measured value is always greater than the high threshold (0) or lesser than the low threshold (255). The PROX interrupt occurs after every measurement. The mechanism of ALS interrupt is same as the PROX interrupt. Therefore ALS low threshold is set to the maximum (4095) and ALS high threshold is set to the minimum (0). As a result, ALS measured value is always greater than the high threshold (0) or lesser than the low threshold (4095). The ALS interrupt occurs after every measurement. 5 / 17

6 Table Initializing process parameter list Processing Brownout check initialization Interrupt setting PROX back-scatter setting ALS sensitivity range setting PROX sleeping time setting ALS IR compensation setting Start measurement Register name Addr Setting Index (Parameter) ess value Description INTERRUPT 0x04 4 0b0 Clear brownout detected flag. (SUPPLY_FLAG) INTERRUPT 0x04 7 0b0 Clear PROX interrupt flag. (PROX_FLAG) INTERRUPT 0x04 6:5 0b00 Set Proximity persistency to 1. (PROX_PRST) INTERRUPT 0x04 3 0b0 Clear ALS interrupt flag. (ALS_FLAG) INTERRUPT 0x04 2:1 0b00 Set ALS persistency to 1. (ALS_PRST) INTERRUPT 0x04 0 0b0 Interrupt is active at either PROX (INT_CTRL) or ALS PROX_TH1 0x05 7:0 0xFF Set PROX low threshold to 255. PROX_TH2 0x06 7:0 0x00 Set PROX high threshold to 0. ALS_TH1 0x07 7:0 0xFF Set ALS low threshold to ALS_TH2 0x08 7:0 0xF0 Set ALS high threshold to 0. ALS_TH3 0x09 7:0 0x00 CONFIGURE1 (INT_TYPE) 0x02 7 0b1 Set PROX interrupt scheme to a window comparator scheme. CONFIGURE1 0x02 6:3 0b0000 Set PROX back-scatter (PROX_BSCAT) adjustment to minimum setting. Refer to 8. 2 Measurement Proximity Offset on a datasheet. CONFIGURE1 0x02 1:0 0b11 Set ALS range to (ALS_RANGE) CONFIGURE0 0x01 4:2 0b001 Set the sleeping time between (PROX_SLP) PROX detections to 100 msec. CONFIGURE2 0x03 4:0 0b10000 Set ALS IR compensation to (ALS_KN) default setting. Refer to 8. 2 Measurement ALS IR Compensation on a datasheet. CONFIGURE0 0x01 5 0b1 Start measurement of PROX. (PROX_EN) CONFIGURE1 0x02 2 0b1 Start measurement of ALS. (ALS_EN) 6 / 17

7 The setting values in the table can be changed. To find out optimal setting values, please follow the following procedure. Interrupt setting Appropriate threshold settings can reduce the number of wasteful register reading from the host. For example, if the ALS_DT is 1000 then set ALS low threshold to 500 and set ALS high threshold to As a result, interrupt does not occur until ALS_DT value gets to more than 1500 or less than 500. PROX back-scatter setting PROX_BSCAT=0b0000 means No proximity offset cancellation. Each count subtracts about 32 counts from the proximity offset data. Procedure to determine PROX back-scatter setting is as follows: With no IR reflective object in the field of view of, adjust PROX_BSCAT to minimize the proximity data count. Note that the proximity data count should always be more than zero. ALS IR compensation setting Programmable active IR compensation fine-tunes ALS performance for specific glass. Optimize the measurement variation between various IR-content light sources. IR compensation value depends on chip coating variation and customer optical solution, mechanical solution & glass type. Tuning is required most when the glass is very dark < 10% visible. If the customer does not know the optical / mechanical layout, the customer should use code: 0b b00000: Minimum IR compensation 0b10000: Default 0b11111: Maximum IR compensation IR compensation range 2.1% ALS_KN 0.1% (EQ ) Procedure to determine ALS IR Compensation setting is as follows: Step 1: Measure the ALS counts and lux level under a white LED light source without IR spectrum. Step 2: Measure the ALS counts and lux level under a 850nm IR LED and above white LED light sources. Step 3: Adjust IR compensation for ALS (Reg 0x03, Bits 4:0) until IR LED light source contribution is under 10%. 7 / 17

8 2.2 Interrupt handling Application Note Clear interrupt Clear interrupt is achieved by writing 0 to each bit of INTERRUPT (address: 0x04) from the host side. In case of clearing all interrupts, write 0 to each bit of INTERRUPT including bit 7 and bit 3. In order to remove the possibility of clearing interrupts accidentally, write 1 to the bit which should not be cleared. Writing 1 to the bit which value is 0 results in nothing. The value does not turn to 1 and remains being 0. Of course writing 1 to the bit which value is 1 results in nothing Read measurement data The measurement data is read from 4 registers; PROX_DT@0x0A, ALS_DT1@0x0B, ALS_DT2@0x0C and PROX_WASH@0x0D. ALS_DT is 12 bit length and stored in ALS_DT1 and ALS_DT2 as MSB and LSB respectively. If PROX_WASH bit (PROX_WASH@0x0D, bit 0) is 0b1, PROX_DT is always 0x Signal processing The signal processing of illuminance calculation and proximity determination uses the measurement data of ALS_DT1, ALS_DT2, PROX_DT and PROX_WASH. The illuminance calculation uses the measured value of ALS_DT1 and ALS_DT2. The proximity determination uses the PROX_DT and PROX_WASH Calculating equation of illuminance The s ADC output codes are directly proportional to lux. E α OUT EQ In Equation , E is the calculated lux reading and OUT represents the ADC code. The constant α to plug in is determined by the range bit ALS_RANGE (register 0x02 bit 1:0) and is independent of the light source type. Table shows four different scale factors. Table ALS Sensitivity at different ranges ALS_RANGE α RANGE (LUX/Count) / 17

9 2.2.5 Proximity determination method In the proximity detection, the sensor emits the infrared light and the proximity detection is achieved by comparing the infrared light reflection value and the threshold. You can get the measured infrared light reflection value by reading PROX_DT register. An example of relationship between sensor-object distance and PROX_DT is shown in Figure PROX_DT [a.u.] Distance to Gap to Cover glass with Glay card (18%) [mm] Figure An example of relationship between sensor-object distance and PROX_DT Two thresholds for the reflected infrared light are adopted to determine the adjacency of an object with hysteresis (Figure ). Since it is considered that the more PROX_DT (amount of reflection value), the more adjacent an object is, when the PROX_DT exceeds the upper threshold, it determines that an object is adjacent and when the PROX_DT falls below the lower threshold, it determines that an object is not adjacent. PROX_DT Upper threshold Not adjacent Adjacent Not adjacent Lower threshold Time Figure An example of proximity judgment with two thresholds 9 / 17

10 3. Sample code /*-+-*-+-*-+-*-+-*-+-*-+-*-+-*-+-*-+-*-+-*-+-*-+-*-+-*-+-*-+-*-+-*-+-*-+-*-+-*-+ * Copyright (c) 2014 Murata Manufacturing Co., Ltd. All Rights Reserved. *-+-*-+-*-+-*-+-*-+-*-+-*-+-*-+-*-+-*-+-*-+-*-+-*-+-*-+-*-+-*-+-*-+-*-+-*-+-*-+* * CREATE : 2014/08/19 * VERSION : 1.0 *-+-*-+-*-+-*-+-*-+-*-+-*-+-*-+-*-+-*-+-*-+-*-+-*-+-*-+-*-+-*-+-*-+-*-+-*-+-*-*/ /******************************************************************************* 1. MURATA AND ITS AFFILIATES SHALL NOT BE LIABLE TO LICENSEE OR TO ANY OF LICENSEEA AND ITS AFFILIATES SHALL NOT BE LIABLE TO LICENSEE OR TO ANY OF ** PUNITIVE, OR CONSEQUENTIAL DAMAGES ARISING OUT OF OR RELATING TO THE LICENSING OR USE OF THE SOFTWARE OR FOR ANY ERROR OR DEFECT IN THE SOFTWARE. 2. THE SOFTWARE IS LICENSED R ANY ERROR OR DEFECT IN THE SOFTWARE. E REPRESENT OR WARRANT THAT ERRORS IN THE SOFTWARE WILL BE CORRECTED OR THAT THE SOFTWARE WILL RUN ERROR-FREE. THERE ARE NO WARRANTIES COVERING THE SOFTWARE, EITHER EXPRESS OR IMPLIED, INCLUDING WITHOUT LIMITATION ANY WARRANTY OF DESIGN, MERCHANTABLITY, FITNESS FOR A PARTICULAR PURPOSE, OR AGAINST INFRINGEMENT OF INTELLECTUAL PROPERTY RIGHTS. 3. LICENSEE SHALL INDEMNIFY MURATA AND ITS AFFILIATES AND HOLD THEM HARMLESS FROM ANY AND ALL LIABILITIES, CLAIMS, COSTS, LOSSES, AND EXPENSES INCLUDING, BUT NOT LIMITED TO, REASONABLE ATTORNEYSSTS, LOSSES, AND EXPENSES INCLUDING, MURATA AND ITS AFFILIATES, OR BOTH, ARISING OUT OF OR RELATING TO LICENSEE S MISUSE, MODIFICATION, UPGRADE, ADDITIONS, ALTERATION, MARKETING, DISCLOSURE, SALE, SUBLICENSING, OR OTHER DISTRIBUTION OF THE SOFTWARE. *******************************************************************************/ #define U8 unsigned char #define U16 unsigned short #define S16 signed short #define U32 unsigned long int #define S32 signed long int #define REG_CHIPID 0x00U #define REG_CONFIGURE0 0x01U #define REG_CONFIGURE1 0x02U #define REG_CONFIGURE2 0x03U #define REG_INTERRUPT 0x04U #define REG_PROX_TH1 0x05U #define REG_PROX_TH2 0x06U #define REG_ALS_TH1 0x07U #define REG_ALS_TH2 0x08U #define REG_ALS_TH3 0x09U #define REG_PROX_DT 0x0AU #define REG_ALS_DT1 0x0BU #define REG_ALS_DT2 0x0CU #define REG_PROX_WASH 0x0DU typedef enum LT1PA01_Sensitivity_ LT1PA01_ALS_62 = 0, LT1PA01_ALS_125, LT1PA01_ALS_1000, LT1PA01_ALS_2000 LT1PA01_Sensitivity; 10 / 17

11 typedef enum LT1PA01_PROX_STATUS_ LT1PA01_PROX_STATUS_NOT_ADJACENT = 0, LT1PA01_PROX_STATUS_ADJACENT = 1 LT1PA01_PROX_STATUS; typedef struct LT1PA01_PROX_CONFIG_ U8 upper_threshold; U8 lower_threshold; LT1PA01_PROX_CONFIG; void LT1PA01_init(void); void LT1PA01_clear_interrupt(U8* interrupt); void LT1PA01_PROX_read_data(U8* prox_dt, U8* prox_washout); void LT1PA01_ALS_read_data(U16* als_dt); float LT1PA01_ALS_calc(U16 als_dt, LT1PA01_Sensitivity als_range); LT1PA01_PROX_STATUS LT1PA01_PROX_calc(U8 prox_dt); void LT1PA01_WriteToRegister(U8 reg, U8 value) /* Please describe the I2C Single Write operation according to */ /* the host environment. */ U8 LT1PA01_ReadFromRegister(U8 reg) /* Please describe the I2C Single Read operation according to */ /* the host environment. */ return 0U; void LT1PA01_WriteToRegisters(U8 reg, U8* value, U8 num) /* Please describe the I2C Burst Write operation according to */ /* the host environment. */ void LT1PA01_ReadFromRegisters(U8 reg, U8* value, U8 num) /* Please describe the I2C Burst Read operation according to */ /* the host environment. */ U8 IntFlg = 0U; void inerrupt_handler(void) /* This function is supposed to be called when INT pin interrupt occurs. */ IntFlg = 1U; /* Initializing process */ void LT1PA01_init (void) 11 / 17

12 U8 data = 0U; /*-- * Brownout check initialization * Interrupt setting *-*/ /* INTERRUPT PROX_FLAG: Clear PROX interrupt flag. PROX_PRST: Set Proximity persistency to 1 conversion. SUPPLY_FLAG: Clear brownout detected flag. ALS_FLAG: Clear ALS interrupt flag. ALS_PRST: Set ALS persistency to 1 conversion. INT_CTRL: Interrupt is active at either PROX or ALS */ data = 0x00U; LT1PA01_WriteToRegister(REG_INTERRUPT, data); /*-- * Interrupt setting *-*/ /* PROX low threshold = 255 (0xFF) PROX high threshold = 0 (0x00) ALS low threshold = 4095 (0xFFF) ALS high threshold = 0 (0x000) */ LT1PA01_WriteToRegister(REG_PROX_TH1, 0xFFU); LT1PA01_WriteToRegister(REG_PROX_TH2, 0x00U); LT1PA01_WriteToRegister(REG_ALS_TH1, 0xFFU); LT1PA01_WriteToRegister(REG_ALS_TH2, 0xF0U); LT1PA01_WriteToRegister(REG_ALS_TH3, 0x00U); /*-- * Interrupt setting * PROX back-scatter setting * ALS sensitivity range setting *-*/ /* CONFIGURE 1 INT_TYPE: Set to a window comparator scheme. PROX_BSCAT: Set to minimum setting. ALS_EN: ALS_RANGE: Set to */ data = 0x83U; LT1PA01_WriteToRegister(REG_CONFIGURE1, data); 12 / 17

13 /*-- * PROX sleeping time setting *-*/ /* CONFIGURE 0 Reserved: PROX_EN: PROX_SLP: Set to 100 msec. Reserved: */ data = 0x04U; LT1PA01_WriteToRegister(REG_CONFIGURE0, data); /*-- * ALS IR compensation setting *-*/ /* CONFIGURE 2 Reserved: ALS_KN: Set to default setting */ data = 0x10U; LT1PA01_WriteToRegister(REG_CONFIGURE2, data); /*-- * Start measurement *-*/ /* CONFIGURE 0 Reserved: PROX_EN: Start measurement of PROX PROX_SLP: Reserved: */ data = 0x24U; LT1PA01_WriteToRegister(REG_CONFIGURE0, data); /* CONFIGURE 1 INT_TYPE: PROX_BSCAT: ALS_EN: Start measurement of ALS ALS_RANGE: / 17

14 */ data = 0x87U; LT1PA01_WriteToRegister(REG_CONFIGURE1, data); /* Clear Interrupt source */ void LT1PA01_clear_interrupt(U8* interrupt) /* Specify the interrupt source. */ *interrupt = LT1PA01_ReadFromRegister(REG_INTERRUPT); if ((*interrupt & 0x10U)!= 0U) /* INTERRUPT PROX_FLAG: PROX_PRST: SUPPLY_FLAG: Brownout detected ALS_FLAG: ALS_PRST: INT_CTRL: */ /* Please describe the code to do after brownout detection. */ if ((*interrupt & 0x80U)!= 0U) /* INTERRUPT PROX_FLAG: PROX interrupt, Write 0 to clear PROX_PRST: SUPPLY_FLAG: Write 1 to NOT clear ALS_FLAG: Write 1 to NOT clear ALS_PRST: INT_CTRL: */ /* Clear interrupt source. */ LT1PA01_WriteToRegister(REG_INTERRUPT, ((*interrupt 0x18U) ^ 0x80U)); if ((*interrupt & 0x08U)!= 0U) /* INTERRUPT PROX_FLAG: Write 1 to NOT clear PROX_PRST: SUPPLY_FLAG: Write 1 to NOT clear 14 / 17

15 ALS_FLAG: ALS interrupt, Write 0 to clear ALS_PRST: INT_CTRL: */ /* Clear interrupt source. */ LT1PA01_WriteToRegister(REG_INTERRUPT, ((*interrupt 0x90U) ^ 0x08U)); return; /* Read measurement data of ALS */ void LT1PA01_ALS_read_data(U16* als_dt) U8 data[2u]; /* data[0u]: ALS_DT1 (MSB) data[1u]: ALS_DT2 (LSB) */ LT1PA01_ReadFromRegisters(REG_ALS_DT1, data, 2U); *als_dt = (U16)data[1U] + (U16)(((U16)data[0U])<<8); return; /* Read measurement data of PROX */ void LT1PA01_PROX_read_data(U8* prox_dt, U8* prox_washout) *prox_dt = LT1PA01_ReadFromRegister(REG_PROX_DT); *prox_washout = LT1PA01_ReadFromRegister(REG_PROX_WASH); return; /* Signal processing for ALS */ float LT1PA01_ALS_calc(U16 als_dt, LT1PA01_Sensitivity als_range) float LuxPerCounts[4] = , , , /* Refer to Table */ ; float lux; lux = (float)als_dt * LuxPerCounts[als_range]; return lux; /* Signal processing for PROX */ LT1PA01_PROX_STATUS LT1PA01_PROX_calc(U8 prox_dt) static LT1PA01_PROX_STATUS prox_status = LT1PA01_PROX_STATUS_NOT_ADJACENT; LT1PA01_PROX_CONFIG prox_config; prox_config.upper_threshold = 80U; /* TBD Depend on Customer setting */ prox_config.lower_threshold = 40U; /* TBD Depend on Customer setting */ 15 / 17

16 if (prox_status == LT1PA01_PROX_STATUS_NOT_ADJACENT) if (prox_dt > prox_config.upper_threshold) prox_status = LT1PA01_PROX_STATUS_ADJACENT; else if (prox_dt < prox_config.lower_threshold) prox_status = LT1PA01_PROX_STATUS_NOT_ADJACENT; return prox_status; void main (void) U8 prox_dt = 0U; U8 prox_washout = 0U; U16 als_dt = 0U; U8 interrupt = 0U; float lux = 0.0F; LT1PA01_PROX_STATUS prox_status = LT1PA01_PROX_STATUS_NOT_ADJACENT; LT1PA01_init(); while (1) /* This flag is supposed to be set after INT pin interrupt occurs. */ if (IntFlg!= 0U) IntFlg = 0U; /* Clear Interrupt source */ LT1PA01_clear_interrupt(&interrupt); if ((interrupt & 0x80U)!= 0U) /* INTERRUPT PROX_FLAG: PROX interrupt PROX_PRST: SUPPLY_FLAG: ALS_FLAG: ALS_PRST: INT_CTRL: */ /* Read measurement data of PROX */ LT1PA01_PROX_read_data(&prox_dt, &prox_washout); 16 / 17

17 if ((prox_washout & 0x01U)!= 0U) /* PROX_WASH PROX_DAC: PROX_WASH: Ambient light saturation */ /* Assumption that there is no object */ prox_status = LT1PA01_PROX_STATUS_NOT_ADJACENT; else /* Signal processing for PROX */ prox_status = LT1PA01_PROX_calc(prox_dt); if ((interrupt & 0x08U)!= 0U) /* INTERRUPT PROX_FLAG: PROX_PRST: SUPPLY_FLAG: ALS_FLAG: ALS interrupt ALS_PRST: INT_CTRL: */ /* Read measurement data of ALS */ LT1PA01_ALS_read_data(&als_dt); /* Signal processing for ALS */ lux = LT1PA01_ALS_calc(als_dt, LT1PA01_ALS_2000); /*-+-*-+-*-+-*-+-*-+-*-+-*-+-*-+ end of file +-*-+-*-+-*-+-*-+-*-+-*-+-*-+-*-+*/ 17 / 17

VDD_PULLUP 250 VDD SCL, SDA

VDD_PULLUP 250 VDD SCL, SDA DATASHEET ISL29147 Low Power Ambient Light and Proximity Sensor with Enhanced Infrared Rejection FN8409 Rev 3.00 The ISL29147 is a low power Ambient Light Sensor (ALS) and proximity (PROX) sensor. It has