ADC and SD Card Data Logger Problem

Using Arduino Sensors
1

Hi.

I am making a SD card data logger that converts the analog data from UV sensors to digital data, then stores it in an SD card.

UV sensor: https://cdn.sparkfun.com/datasheets/Sensors/LightImaging/ML8511_3-8-13.pdf

The sensor has 1 V output in no light environment and up to 3V under intense UV. I use 100K pull-up resistor as directed in the datasheet. The Arduino Uno has a 10 bit ADC. I want to the ADC to have more effective resolution; therefore, I put 3.3V on the Arduino Uno board to AREF. However, I also use the same 3.3V pin to power 3 UV sensors.

The problem is that the ADC converts the sensor's 1V output to 260, I think it should be about 300. Then, I connect 1V from a DC power supply to the ADC. It produces 980. When I connected the onboard 3.3V and ground to the ADC. It produces correct outputs: 1023 and 0, respectively.

I suspect that the onboard 3.3V pin can't produce enough current to power the sensors and AREF. Maybe I should get a 3.3V regulator.

What do guys think? I have also attached the code.

Thank you.

SD datalogger.txt (2.69 KB)

2

The sensor datasheet says that normal supply current is 300uA so the 3 are pulling less than 1mA.

3

The problem is that the ADC converts the sensor's 1V output to 260, I think it should be about 300. Then, I connect 1V from a DC power supply to the ADC. It produces 980. When I connected the onboard 3.3V and ground to the ADC. It produces correct outputs: 1023 and 0, respectively.

check and check, with a multimeter to ensure the input voltage.