I am doing a project on automating a hydroponic system to grow tomatoes. I need a TDS sensor to measure Total Dissolved salts. I searched a lot for a sensor but I was not able to find a sensor that satisfies my requirement. I need a sensor that can measure high ppm. But, the sensors are only capable of measuring 1000ppm. Some Handheld TDS meters which give digital output are capable of measuring (0 - 9990 ppm). Is there a way to get the value that shows in digital display on handheld TDS meter to a raspberry pi so that I can trigger a process depending on the value? I am okay with performing any task to make this possible. I am wondering if there is a way to change any wire connections and connecting them to pi which gives the solution. Any suggestions, please??
Some Handheld TDS meters:
amazon
mi

 

Just because a display shows 4 digits, does not mean its actually better than a 3 digit sensor.

I had a DMM, that had 9 digits, from china, hat did not mean it could measure uv to Kv,
the lower bits are just noise.

You can make more digits from a sensor by filtering,
I'm going to drop back to base 2 now.
if you have 1 reading, with a random error / noise on it
then if you average 4 samples, you gain one extra digital bit.
so a 8 bit sample becomes a 9 bit number when you average 4 samples.

How many samples per second can you take ?
how frequent do you actually want updates ?