Sensors Knowledge Base

      • Si1153 Power Consumption

        TonyQ | 12/348/2017 | 06:06 PM


        How to calculate the total power consumption of Si1153? What are the major factors that impact power consumption?


        A detailed power consumption breakdown of Si1153 is covered in Section 6 of the application note AN950:

        There're a total of 4 current consumption values used in the equation:

        1. Standby Current: 1.25uA (Vdd = 3.3V)

        2. Active Current (internal controller processing): 4.5mA (Vdd = 3.3V)

        3. ADC Current (suspend mode): 0.525mA (Vdd = 3.3V)

        4. LED Current: set by the host

        Since the standby current is relatively small comparing to the rest, we can ignore that to simplify the estimation.

        I = I_internal_controller + (I_adc_setup + I_adc_active) + I_led

        The integration time of the ADC is controlled by the HW_GAIN setting. The default integration time is 24.4us and 24.4*2^HW_GAIN if HW_GAIN is set to non-zero values.

        The internal controller processing time per measurement is 155us. The ADC setup time is 48.8us. The si1153 sensor will perform 2 back-to-back measurements, one with the LED on and the other with the LED off. Therefore, if we assume integration time is set to default and LED current is set to maximum 354mA, the total power consumption will be:

        I = (155us * 4.5mA + 48.8us * 525uA + 2* 24.4us * 525uA + 24.4us * 354mA) * Fs

        where Fs is the sampling frequency of the measurement.


      • Si1153/33 Ambient Light Sensing and LUX calculation

        TonyQ | 12/348/2017 | 03:47 PM


        Can Si1153/33 sensors be used for ambient light sensing? How to convert ALS results to LUX values? Any example code available?


        Only Si1153-AA00-GM and Si1133-AA00-GM parts can measure ambient light. Si1153-AA09-GM and Si1153-AA9X-GM parts cannot measure ambient light due to the on-die 940nm filter.

        There's no simple equation to convert ALS measurement results to LUX values by any means. The only solution is to perform tests under certain light sources and calibrate ALS results against LUX values read from a LUX meter. Then find the ratio or formula to estimate LUX values based on ALS measurement data. Since it's an estimation, the accuracy won't be anywhere close to a LUX meter. Si1153/33 sensors CANNOT be used in LUX meter type of applications, but can still be used in applications that only require an approximate LUX level.

        We've built a model to use 3 different channels' ALS measurement results to estimate LUX values. The example code is attached. However, the model is overly complicated and we recommend the customer to only use that as a reference and develop their own equation to estimate LUX.

        Silicon Labs doesn't support ALS calibration for any applications.

      • Si1153 3D Gesture Detection

        TonyQ | 12/348/2017 | 02:56 PM


        Can Si1153 be used for 3D gesture detection applications? How's the performance look like? Any example code available?


        Yes, Si1153 can be used for short-range 3D gesture detection applications. We have a gesture detection demo running on our Si115X-OPT-EXP board. The customer can download the Si115x GUI from our website and select the gesture demo from the GUI's main panel. Here's the software download link:

        The gesture detection demo can detect swiping left, right, up, down and moving near, far gestures. The reliable detection range is up to approximately 20cm. Increasing the sampling frequency can help to improve the performance of detecting fast moving objects. 

        The example code for the basic gesture detection algorithm (swipe left, right, up and down) is also available under the installation directory: C:\SiliconLabs\Optical_Sensors\Si115x\source\si115x_lib\Gesture example

        We've attached the example code in the article here in case the customer cannot install the GUI software.

      • Si1133 Calibration and UV Index Calculation

        TonyQ | 12/347/2017 | 06:05 PM


        How to calibrate Si1133? How is UV index calculated?


        To achieve the best performance, calibration is essential for Si1133 because of sensor-to-sensor and unit-to-unit variation in sensor's placement with respect to the diffuser (or window opening), as well as the variation in the material of the overlay and the diffuser. We recommend the customer to perform calibration on the prototype after the optical design is completed.

        There're 2 options for the light source in the calibration procedure, one is to use the sun and the other is to use a solar simulator. A commercial UV index meter is also required as the reference. Here're the basic steps for calibration. First of all, set up a test such that the Si1133 sensor and the UV meter can be placed at the same location under the light source. Secondly, log multiple readings of both the sensor and the UV meter across different UV index levels (0 ~ 10 UVI). Lastly, fit the result to a second-order polynomial equation:

        UV_index_reading = k(m × Si1133_raw_data ^ 2 + Si1133_raw_data)

        The coefficients k&m can be later used to calculate UV index based on Si1133's readings.

        Silicon Labs provides default configuration and coefficients to calculate UV index as well as optical design recommendations in the UV application note AN968:

        The software example code is also attached.

      • Can the Si72xx Hall effect sensors be field programmed?

        jogammel | 11/325/2017 | 10:39 AM

        The Si7210 I2C parts are programmable for many features. Some features such as the sleep timer are not user programmable.

        The Si720x and Si721x series of parts are not user programmable.

        There are many possible factory configuration options for the Si72xx series of Hall-effect sensors. Please contact your sales representative if you do not see the specific combination of output type, sensitivity, sample rate, etc. that you need.

      • What are the advantages of Si72xx hall-effect sensors compared to similar devices from other suppliers?

        jogammel | 11/325/2017 | 10:36 AM

        The SOT-23 and TO92 versions of the Si72xx series of sensors are pin compatible with similar devices from many suppliers.

        The Si72xx Hall effect sensors excel in:

        • low power
        • high sensitivity
        • linearity
        • low offset
        • accurate gain

        The tamper detection feature  (detection of a stronger than expected field) is unique. I2C parts which allow digital output of the magnetic field data and user programmed operate and release points are not common.

      • Are drivers and example code available for the Si72xx hall-effect sensors?

        jogammel | 11/325/2017 | 10:35 AM

        The simple 3 and 5 pin sensors in the Si720x and Si721x series generally do not need a driver or example code. Just apply power and ground and the output pin will go high or low with magnetic field. Decoding the PWM or SENT data from parts with these output type is included in the source code for the Si72xx-WD-Kit which is available in simplicity studio.

        The Si7210 I2C sensors can be a little more difficult to work with and drivers are available through simplicity studio.

        Example code and typical uses case descriptions are also available in AN1018.

      • What demonstrations are available for the Si72xx hall-effect sensors?

        jogammel | 11/325/2017 | 10:34 AM

        The Si72xx-WD-Kit includes demonstrations for wheel position sensing, wheel rotation counting, and display of the magnetic field data from sensors and small postage stamp sized evaluation boards. This demonstration uses the MCU and display from a pre-programmed EFM32TM Happy Gecko STK.

        The Si72xx-Eval-Kit will be available January 2018 and includes a USB adapter to power the postage stamp sized boards and a PC GUI to display the sensor data.

        The Thunderboard Sense wireless multiprotocol sensor demonstration platform includes a hall-effect sensor and can display the sensor data through a mobile app.

      • Are there soldering considerations with the Si72xx sensors?

        jogammel | 11/325/2017 | 10:34 AM

        We have noticed a small variation in offset related to package stress when the sensors are solders by hand. In most cases, this can be recovered by solder touch up.  We have not seen issues related to other soldering techniques.

      • How do hall-effect sensors compare to other sensors based on magneto-resistance effects?

        jogammel | 11/325/2017 | 10:33 AM

        Hall-effect sensors are inherently more linear and do not have “hysteresis” effects from strong magnetic field. Some magneto-resistance sensors can be damaged by very strong field.

        Magneto-resistive sensors are generally sensitive in the direction of magnetic field parallel to the PCB. In most cases, it is possible to order the magnet with a different polarization to produce magnetic field in the desired axis.