***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? ***Short Answer*** > Some months ago I played with a couple of moisture sensor / level > detectors. Below is an example. [![water level sensor][1]][1] [Water Level Detection Discussion - Rpi StackExchnge][2] 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". [![level sensor resistance][3]][3] 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) [![PCF8592][4]][4] [![mcp3x020408][5]][5] ***Long Answer*** */ long answer to prune later, ...* *Introduction and Summary* */ to continue, ...* *Question Analysis* > 1. I think the preliminary functional spec of the project is very good, because it is concise and precise. > > 2. There are many reasons that the question is so short, but I will not list my wild guesses for now. Perhaps later. > > 3. The spec includes the following key words/phrases: > > "***Rpi, ADC, tank level sensor, 20Ω ~ 200Ω***. > > 4. 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". > > 5. 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][2] [AliExpress Level Sensors][6] [AliEXpress Non-contact Level Sensors][7] [AliExpress10A/250V Water Level Controller Module][8] [AliExpress Water level sensor Water drops tester][9] [AliExpress 5~24V 5mA Non-contact Induction Water Level Sensor][10] [Gig (ee, rpi, arduino) projects][11] [ph Sensor using sensor and ADCs PCF8591 and MCP3208][12] */ to continue, ...* [1]: https://i.sstatic.net/GVzFX.png [2]: https://raspberrypi.stackexchange.com/questions/98491/water-level-detection-sensor-3-3-volt-vs-5-volt/98497#98497 [3]: https://i.sstatic.net/qwbje.jpg [4]: https://i.sstatic.net/3HBCm.png [5]: https://i.sstatic.net/S8JHz.png [6]: https://www.aliexpress.com/w/wholesale-level-sensor.html [7]: https://fr.aliexpress.com/item/Non-contact-Pipe-Level-Sensors/32255031027.html?spm=a2g0w.search0104.3.265.531f76856zZiC8&ws_ab_test=searchweb0_0,searchweb201602_9_10065_10068_319_10059_10884_317_10887_10696_321_322_10084_453_10083_454_10103_10618_10307_537_536,searchweb201603_51,ppcSwitch_0&algo_expid=af3cfe02-0556-4738-a8ae-46353f4edbf3-33&algo_pvid=af3cfe02-0556-4738-a8ae-46353f4edbf3 [8]: https://fr.aliexpress.com/item/10A-250V-Water-Liquid-Level-Controller-Module-Automatic-Water-Level-Detection-Sensor-Temperature-Sensor-Water-Level/32820105118.html?spm=a2g0w.search0104.3.310.531f76856zZiC8&ws_ab_test=searchweb0_0,searchweb201602_9_10065_10068_319_10059_10884_317_10887_10696_321_322_10084_453_10083_454_10103_10618_10307_537_536,searchweb201603_51,ppcSwitch_0&algo_expid=af3cfe02-0556-4738-a8ae-46353f4edbf3-39&algo_pvid=af3cfe02-0556-4738-a8ae-46353f4edbf3 [9]: https://fr.aliexpress.com/item/DC-3-5V-High-Sensitivity-Water-Liquid-Level-Sensor-Tester-Water-Level-Monitoring-Measuring-Tool-Water/32814866978.html?spm=a2g0w.search0104.3.216.620d755cWn7ee7&ws_ab_test=searchweb0_0,searchweb201602_9_10065_10068_319_10059_10884_317_10887_10696_321_322_10084_453_10083_454_10103_10618_10307_537_536,searchweb201603_51,ppcSwitch_0&algo_expid=276db9f8-3b68-4295-a2c2-1516543028cd-31&algo_pvid=276db9f8-3b68-4295-a2c2-1516543028cd [10]: https://fr.aliexpress.com/item/D-tecteur-de-niveau-de-liquide-5-24-V-5mA-capteur-de-niveau-de-liquide-sans/32971512924.html?spm=a2g0w.search0104.3.269.5eb5755cG2N9tK&ws_ab_test=searchweb0_0%2Csearchweb201602_9_10065_10068_319_10059_10884_317_10887_10696_321_322_10084_453_10083_454_10103_10618_10307_537_536%2Csearchweb201603_51%2CppcSwitch_0&algo_pvid=f09e6f0d-a67d-4c18-bace-f8494991ae4c&algo_expid=f09e6f0d-a67d-4c18-bace-f8494991ae4c-43 [11]: https://www.eetasia.com/news/article/EE-Pushed-into-the-Gig-Economy [12]: https://raspberrypi.stackexchange.com/questions/96653/calibrate-ph-4502c-ph-meter