How many different I2C addresses does Si1133 support? How to set them?
Answer
Si1133 supports 2 different I2C addresses. If the AD pin is high during the power-up, the sensor will come up with the default I2C address 0x55. If the AD pin is pulled low during the power-up, the sensor will use the alternate I2C address 0x52.
2. I2C communication failure
Question
Why does the host fail to communicate with the sensor through the I2C interface?
Answer
There're a couple of possible causes:
a. Pin 7 MUST be pulled high during the power-up. If it's not, the sensor won't be powered up properly.
b. Check the I2C address and make sure that the correct I2C address is used.
c. Check the I2C timing specifications and see if that meets the requirement listed in Table 8.3 in the datasheet, especially the I2C frequency and rise/fall time.
3. Power-on reset
Question
Why could the host fail to communicate with the sensor upon power-on reset?
Answer
During the power-on reset, Vdd must drop below 0.5V for the sensor to properly reset itself. If the Vdd is held between 0.5V to 1V, the sensor will enter an unknown state and fail to power up normally.
4. UV index accuracy
Question
What's the UV index accuracy of Si1133?
Answer
With diffuser, the UV index accuracy can reach +/-0.75UVI. Without diffuser, the accuracy is about +/-2UVI.
5. UV spectrum response
Question
What's the UV spectrum response of Si1133 look like?
Answer
Si1133 is responsive to both UVA and UVB wavelength. Silicon Labs does not provide spectrum response information of Si1133.
6. Optical Design
Question
Why do Si1133 require a diffuser?
Answer
All standard UV instruments have diffusers and require the sensor to be facing straight up vertically regardless of where the sun is. Without a diffuser, the UV sensor will have limited view angle. This is the same for competitors’ product.
7. Sensor output
Question
Does the Si1133 output UV Index directly?
Answer
No, the ADC readings need to go through a set of coefficients, and the results will be the UV index. There are two sets of coefficients - one for diffuser designs and one for designs with no diffuser.
KBA_SENS_0302: Si1133 FAQ
1. I2C address
Question
How many different I2C addresses does Si1133 support? How to set them?
Answer
Si1133 supports 2 different I2C addresses. If the AD pin is high during the power-up, the sensor will come up with the default I2C address 0x55. If the AD pin is pulled low during the power-up, the sensor will use the alternate I2C address 0x52.
2. I2C communication failure
Question
Why does the host fail to communicate with the sensor through the I2C interface?
Answer
There're a couple of possible causes:
a. Pin 7 MUST be pulled high during the power-up. If it's not, the sensor won't be powered up properly.
b. Check the I2C address and make sure that the correct I2C address is used.
c. Check the I2C timing specifications and see if that meets the requirement listed in Table 8.3 in the datasheet, especially the I2C frequency and rise/fall time.
3. Power-on reset
Question
Why could the host fail to communicate with the sensor upon power-on reset?
Answer
During the power-on reset, Vdd must drop below 0.5V for the sensor to properly reset itself. If the Vdd is held between 0.5V to 1V, the sensor will enter an unknown state and fail to power up normally.
4. UV index accuracy
Question
What's the UV index accuracy of Si1133?
Answer
With diffuser, the UV index accuracy can reach +/-0.75UVI. Without diffuser, the accuracy is about +/-2UVI.
5. UV spectrum response
Question
What's the UV spectrum response of Si1133 look like?
Answer
Si1133 is responsive to both UVA and UVB wavelength. Silicon Labs does not provide spectrum response information of Si1133.
6. Optical Design
Question
Why do Si1133 require a diffuser?
Answer
All standard UV instruments have diffusers and require the sensor to be facing straight up vertically regardless of where the sun is. Without a diffuser, the UV sensor will have limited view angle. This is the same for competitors’ product.
7. Sensor output
Question
Does the Si1133 output UV Index directly?
Answer
No, the ADC readings need to go through a set of coefficients, and the results will be the UV index. There are two sets of coefficients - one for diffuser designs and one for designs with no diffuser.