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.
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.
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.
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.
Datasheet states the RH sensor cannot go through hot air rework due to possible alteration of the device’s characteristics and damage to the cover during hot air rework. Can hot air rework be used to replace a device on a pcb?
Solder joint touch up can be done with a limit of 5 seconds per lead. It is generally recommended that any other rework be done with a fresh device. The problem is hot air rework can reach temperatures much hotter than the peak temperature of the device. When the cover is heated too much it will shrink very quickly. This happens very easily when air flow is directed from the top of the device. If it is possible to use the hot air tool from the below the PCB there should be no damage to the device or the cover.
Yes, as long as low VOC materials used. Care must be taken so that the materials do not get on the sensor. To protect the sensor when coating is applied to the PCB, use Kapton tape over the package cavity to protect the sensor. With Kapton tape, care must be taken so that coating does not get under the tape and dry. This will peel the protective cover away when the tape is removed. The boards should be cured in a well-ventilated area after. After curing, compare conformal coated boards to a non-coated board to check for accuracy after coating process. Some assembly shops may use a paper cup similar to how masking tape is used to prevent paint from getting in the wrong place. The cup is placed inverted to cover over things that shouldn’t get the conformal coating on them.