Question
Does anyone have any ideas on how I can use RPI with ADC to measure a tank level sensor which has a range of only 20 to 200 ohm?
*** Answer***
Some months ago I played with a couple of moisture sensor / level detectors. Below is an example.
Water Level Detection Discussion - Rpi StackExchnge
However the above sensor does not answer the OP's question, which asks to detect resistance using ADC, not analog or digital voltage levels. So I think I need to start from a variable resistance and check out how to use ADC to measure the resistance, within a range of 20 to 200 ohms.
Long Answer
/ long answer to prune later, ...
Introduction and Summary
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Question Analysis
I think the preliminary functional spec of the project is very good, because it is concise and precise.
There are many reasons that the question is so short, but I will not list my wild guesses for now. Perhaps later.
The spec includes the following key words/phrases:
"Rpi, ADC, tank level sensor, 20Ω ~ 200Ω.
The word "tank", is crucial. She says "tank", not "container", perhaps she wants to indicate that the "tank" is deep , say, not a 5 inches deep fish "bowl" or "pond".
The phrase "20Ω ~ 200Ω" is also crucial. There are basically two types of liquid level sensors: active and inactive. Active sensors are usually 5V or 12V powered, and the sensor output is a DC voltage level. Inactive sensors don't have any power. Usually the sensor is just a reed switch and floating magnet, or a long "resistor" whose resistance varies as the water level. Usually the resistor is far, perhaps 10ft, and up to 1,000 ft from the measuring instrument.
References
Water Level Detection Discussion - Rpi StackExchnge
Gig (ee, rpi, arduino) projects
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