Sensors Knowledge Base

      • Si1133/Si115x Optical Sensor EXP Board Example Project

        TonyQ | 10/303/2017 | 05:58 PM


        Is there an example project working with the Si1133/5x-OPT-EXP evaluation board? If so, where can I get it?


        The only example project we have for Si1133/5x-OPT-EXP evaluation board is built on the EFM8 BusyBee STK. You can download it in the attachment. The project can be imported into the Simplicity Studio v4. For any project related questions, please submit support tickets to the 8-bit MCU support team.

      • Multi RH/T Sensors w/ Same I2C Address

        Daniel_H | 09/272/2016 | 06:31 PM


        More than one RHT sensor is needed on a single I2C bus, however the I2C addresses are the same. How can two or more RHT sensors be used on the same I2C bus?


        The RHT sensors do not have a programmable I2C address. Using a multiplexer and a device select line, multiple RHT sensors can use the same I2C bus. A single NMOS is placed on the SDA line with the drain on the host side and the source on the slave side. 10k pull-up resistors should be placed on both side of the NMOS. The MCU can control the SDA line by the device select.

      • RH readings are greater than 100%RH and rolling over to 0%RH

        Daniel_H | 08/235/2016 | 03:59 PM


        RH data is overflowing and rolling over. What can be done to fix this?


        In cases of severe contamination such as the presence of conductive dust or liquid, readings can become significantly higher and will wrap around. To protect against this, it is recommended to use the factory-installed ePTFE cover. Generally, after contamination a bake and hydrate process will recover accuracy however in severe contamination cases, accuracy may be irrecoverable.

      • Replacing the protective cover for RH sensors

        Daniel_H | 08/235/2016 | 02:56 PM


        Is the sensor’s protective cover replaceable?


        The cover is designed to be compatible with normal convection reflow soldering. The cover is not designed to be replaced. We have seen some customers that use excess heat in soldering and the cover shrinks to the point that it is no longer effective. Some customers have had issues with some conformal coating material drying between the cover and the protective tape used while conformal coating is applied. This results in the protective cover peeling off with the tape when the tape is removed after the conformal coating dries. Both of these issues should be avoided. While the cover can be replaced with care to avoid sensor surface contamination, the recommended rework procedure for a device where the cover has been damaged or has peeled off is to replace the device.

      • Prolonged exposure to high humidity enviornments

        Daniel_H | 08/235/2016 | 02:35 PM


        Sensor's RH readings at high humidity drift over time. After exposure once the humid environment drops to a lower RH, there is a shift in the sensor's accuracy.



        Prolonged exposure to high humidity will cause gradual drift of the humidity sensor. All Si70xx sensors have on-chip heaters that can be used to counter local high humidity, help prevent condensation, and reduce the drift. Please refer to AN607, pg.28, for a more detailed explanation on how to estimate RH with heating. For example, turning on the heater with control setting 0x3 heats the sensor about 5C (depending upon system design) which results in approximately 23% drop in the local RH reading.

      • Optical Sensor Slave Address

        Alan_S | 07/204/2016 | 06:35 PM


        How do I change the slave address on my optical sensor part?


        The Si1132, Si1141, Si1142, Si1143, Si1145, Si1146, and Si1147 have a command that allows you to change the i2c address of the device. This change in address is only temporary and will be cleared back to the default address upon a reset.


        The Si1133 and Si1153 have a hardware pin that causes the device to initialize with an alternate slave address. The pin that causes this change is Pin 6 on both devices. When this pin is pulled down to GND, the device will use its alternate slave address. On the Si1153, the use of the LED driver on this pin is lost when using its alternate slave address.

      • RH sensor's I2C bus is stuck

        Daniel_H | 07/187/2016 | 11:25 AM


        The sensor’s I2C bus is stuck. How can this be fixed?


        A common error when there is noise or a host that is not robust is that the sensor can get in a state where it is driving SDA low expecting to be sending data and the host thinks it is sending data with SDA high. This creates bus contention and can hang the bus. In this case of bus contention, we recommend that the host clocks SCL until SDA is released and then sends a stop and new start.

      • RH sensor driver files

        Daniel_H | 07/187/2016 | 11:12 AM


        Where can the driver files for the sensor be downloaded from?


        The drivers can be downloaded from the Humidity Sensors’ web page under the Tools tab. The link is pasted below:

      • RH sensor in 0C temperature

        Daniel_H | 07/187/2016 | 11:09 AM


        Can the RH sensor measure humidity below 0C? And how can it be tested?


        Yes, the sensor works below 0C. The accuracy drift/temperature must be considered. Testing the RH Sensor below 0C is difficult as most RH chambers cannot control the RH level accurately if not at all when temperature is lowered to 0C or below. To check for accuracy when measuring below 0C, a chilled mirror hygrometer is recommended.

      • Inaccurate RH sensor from Isopropanol

        Daniel_H | 07/187/2016 | 11:04 AM


        Can the RH sensor’s PCB be cleaned with Isopropanol?


        Sensor will become inaccurate if exposed to the fumes from Isopropanol. Generally no clean PCB is recommended. If cleaning is required, use deionized water after using water soluble solder flux with the sensor’s protective cover in place. Water pressure must be kept low to maintain the integrity of the protective cover and not allow entry of water into the sensor cavity, there is a 15 PSI max limit. Leave some PCBs uncleaned so that the cleaned boards can be compared for an accuracy check.