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?
Some months ago I played with a couple of moisture sensor / level detectors. Below is an example.
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.
I very surprisingly found that all the five samples from different manufacturers have the same resistance of 0.5 ohms for each of the two resistive “legs”.
Anyway, I think I can try to use an ADC that can measure my sensor’s 0.5 ohm range, and also the OP’s 20~200 ohm range. I am thinking of starting with the cheapest, and lowest resolution ADC/DAC PCF8591. If its low resolution is not enough for 0.5 ohm range, then perhaps I will try others, such as MCP3x02/04/08. The good thing about PCF8591 is that there is cheapy module available, and programming easy, so is newbie friendly. On the other hand, MCP3x02/04/08 is big family of ADCs, from 12 bits to 18 bits (MCP3404)
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Introduction and Summary
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- 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.
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