MIKROE Light mix-sens Click features advanced proximity measurement, color sense (RGBC+IR), and digital ambient light sensing (ALS). The TMD37253 slim module, from AMS, incorporates an IR LED and factory calibrated LED driver. The proximity detection feature provides object detection (e.g. mobile device screen to the user’s ear) by photodiode detection of reflected IR energy (sourced by the integrated LED). Detect/release events are interrupt-driven, and occur when proximity result crosses upper and/or lower threshold settings. The proximity engine features offset adjustment registers to compensate for unwanted IR energy reflection at the sensor. Proximity results are further improved by automatic ambient light subtraction. The ALS detection feature provides photopic light intensity data. The color photodiodes have UV and IR blocking filters and a dedicated data converters producing 16-bit data. This architecture allows applications to accurately measure ambient light which enables devices to calculate illuminance and color temperature to control display backlight and chromaticity.
Proximity results are affected by three fundamental factors: the integrated IR LED emission, IR reception, and environmental factors, including target distance and surface reflectivity. The IR reception signal path begins with IR detection from a photodiode and ends with the 8-bit proximity result in the PDATA register. A signal from the photodiode is amplified, and offset adjusted to optimize performance. Offset correction or cross-talk compensation is accomplished by adjustment to the POFFSET register. The analog circuitry of the device applies the offset value as a subtraction to the signal accumulation; therefore a positive offset value has the effect of decreasing the results.
The color and ALS reception signal path begins as photodiodes receive filtered light and ends with 16-bit results. The IR photodiode primarily used for proximity sensing is multiplexed with the green channel’s ADC to measure the IR content of ambient light. The color photodiodes are filtered with UV and IR filters. The IR photodiode is filtered to receive only IR. A signal from the RGBC photodiodes simultaneously accumulate for a period of time set by the value in ATIME before the results are available. Measurement of IR must be done in a separate integration because it shares the ADC with the green photodiode. Gain is adjustable from 1x to 128 x to facilitate the operation over a wide range of lighting conditions. Custom LUX equations are used to calculate the amount of ambient light, color temperature, as well as, determine the light type (e.g. LED, fluorescent, incandescent, etc.) using the ALS results.
The TMD37253 module operates at 1.8V power supply with 1.8V I2C bus for reduced power consumption. For integration on Mikrobus, complete voltage regulation and logic level translation has been implemented. Therefore, this Click Board™ is designed to be operated only with a 3.3V logic level. A proper logic voltage level conversion should be performed before the Click board™ is used with MCUs with logic levels of 5V.
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