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Thank you for reading. I have read many other voltage divider explanations and calculators on this site as well as the web. My application is using a voltage divider to lower a possible 5 V signal (output of 5 V pressure sensor) to an input of my ESP32 dev board (doit ESP32devkit1 v4). I will being using ADC. The purpose of the project is a pump controller for the water system at my home.

I understand the concept of the voltage drop across the resistors and the calculation. The thing banging my brain is at what point am I setting the input to the ESP by my voltage divider rather than my pressure sensors? Is the point to keep high values on the divider such that my pressure sensor can overpower the voltage divider? Or am I missing something basic?

In the event of the overpower what values should I pick for a minimum? I am on line power so I'm not worried about battery life. In the end this controller will be using a number of inputs for everything from a second pump sensor to the end of my washer or dryer to weather sensors for the sprinkler system. I short I'm more worried about the concept involved than actual values, I have a good selection of resistors so that should be OK.

Transistor
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Sparky
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    Welcome to EE.SE. You need to provide links in your question to the sensor and any other not-so-popular devices. What is the ADC range of the ESP board? If it is 0 - 5 V and your sensor is 0 - 5 V then you don't need to do anything. "*Overpower*" isn't quite the right word. It's over-voltage that will damage the ADC input. – Transistor Oct 09 '21 at 22:03

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Load regulation of a signal source of impedance Rs is defined by the ratio of Requiv. Load to (load +source) impedance ratio. Thus for load R > 100xRs there is only 1% loss in Vs so normally you can neglect this and just use R dividers in the 10k to 100k range and only be concerned about noise pickup from open loop wire area and inductive noise pickup. Thus adding a load C to suppress noise above 1/2 sampling rate by dB of dynamic range desired might be a consideration.

e.g.

So 17k=Rs and 33k = RL = 3.3./5.0 is example of the result of ratio divided With Req load being 11k and if source impedance is let's say , 110 Ohms then the source is further loaded by 1% error.

If BW is only 1Hz of signal and sampling rate is 100 Hz with 10 bit or 1024 or 60 dB range then you want noise to be -60dB at 50 Hz and above. (If there is any)

  • if sensors are high impedance, you may need to consider a buffer for them.
  • Use twisted pair or STP cable for better immunity.
Tony Stewart EE75
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  • I saw [another solution for a slightly different application](https://electronics.stackexchange.com/a/506318/39903) that suggested the addition of a capacitor across the ADC input and ground. Is that appropriate here (for a 5v signal being read by an ESP32)?? I don't understand the capacitor thing. I just want to read automotive CAN signal with ESP32... Many thx. – zipzit May 10 '22 at 19:58
  • No that's a noise suppression for battery voltage – Tony Stewart EE75 May 10 '22 at 20:18