I am using EVAL-CN0409-ARDZ to prototype a turbidity sensor to measure water turbidity accurately over the range 1NTU - 40NTU remotely with the sensor mounted on site in the site PVC plumbing.. To test the concept, I removed LED2 and PD1 from the EVAL board, and mounted these components into a piece of PVC pipe stub (~30mm dia) and connected the components to the EVAL board using twisted pair wire (~75mm/3" long for each of LED2 and PD1). I have fitted small plastic lenses in front of the LED and PD to provide a barrier between the LED/PD components and the water in the pipe. I have glued the LED and PD into place in the pipe fitting behind the lens barriers, taking care to ensure that the glue is kept away from the face of the LED and PD.. When I perform measurements on this arrangement, with no water yet in the pipe, I am unable to get stable readings for LED2/PD1 combination, while LED1/PD2 combination, still mounted in their original positions on the board provide stable readings. By unstable reading, I mean there is a steady drift over several hours. For example, when I first started testing today, initial reading from ADC was 9929. Over the space of a few minutes this increased steadily to 10022, and then started decreasing so that after 1hr the reading was 9623 and still decreasing. I am maintaining benign measurement conditions during this period (testing is on my desk), yet something is affecting readings. Readings are very sensitive to movement of the connecting wires but I am not allowing any movement during my testing. Is it possible that the glue is interfering in some way with the PD charge transfer? Any suggestions as to what is causing my problems would be appreciated.
Thank you for your interest in EVAL-CN0409-ARDZ (CN0409).
Based on your description above, you have removed the LED and PD from the circuit and attached it to the PVC plumbing. The CN0409…
Based on your description above, you have removed the LED and PD from the circuit and attached it to the PVC plumbing. The CN0409 uses the LED's and PD's in a specific angle and sequence to make the measurements as described on its circuit note. The black attachment is specifically designed for the correct angle and ambient light rejection for accurate measurements.
The circuit uses calibration solutions placed in vials for the most accurate readings. Stray light will also contribute to inaccuracy and stability of your reading.
Do you mind sending a picture of your setup?
Closing this due to inactivity, presumed answered.