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I need to realize a circuit that converts an analog signal from [-24V,24V] to [0V,3.3V] before sending that signal to an ADC "MCP3208". I found the circuit in the picture below and it works perfectly in simulation, but I am still not sure if can I use it to send the signal to an ADC input or not. I use the capacitor as a bypass to avoid AC noise if it exists but normally the input signal is DC.

enter image description here

Will this circuit work? If not, what different circuit would work?

user2943160
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berem
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    Make sure you consider any source impedance of your -24V to +24V input, as this could affect the resulting translation. If it is not low enough impedance, you might need to scale all the Rs up. – MikeP Apr 29 '16 at 14:18
  • What's the tolerance on the 3.3V? – EM Fields Apr 29 '16 at 14:25
  • @EMFields MCP3208 inputs are from -0.6V to Vdd+0.6V my Vdd is 3.3V. – berem Apr 29 '16 at 14:34
  • That's not what I asked about. How close to 3.3V does the CH2 signal have to be when it's supposed to be at 3.3V? – EM Fields Apr 29 '16 at 14:37
  • @EMFields The ADC is 12-bit type so the LSB is 0.0008 so it is very close. – berem Apr 29 '16 at 14:48
  • What does your [-24V, +24V] signal look like? Is this battery monitoring or another signal sounce? – user2943160 Apr 29 '16 at 15:10
  • @user2943160 It is just a DC signal with a fixed voltage, the voltage can be any value between -24V and a 24V I don't know what is the source exactly it can be anything but I don't think that will make any difference since I know the voltage and nature of the signal. – berem Apr 29 '16 at 15:16
  • Then you probably want an operation amplifier of some sort to translate between ±24V and 0-3.3V, however this may require a dual high-voltage supply on the microcontroller board. A regular op-amp may work or something more specialized like http://www.linear.com/product/LT6375 would be better, depending on your application. – user2943160 Apr 29 '16 at 15:28
  • @user2943160 What is the problem of my circuit ? – berem Apr 29 '16 at 15:30
  • @berem the passive circuit will not be very accurate across the input range and will be very sensitive to component variation. An active circuit with an op-amp will likely be more consistent across input range and may reduce the effect of component variation. – user2943160 Apr 29 '16 at 15:39
  • Possible solution for passive circuit: http://electronics.stackexchange.com/a/15941/32787 – user2943160 Apr 29 '16 at 15:44
  • There may be no problem, but it all depends on how much error you can accept in your system. for example, let's say your ADC reads 3.300 volts. If your system were perfect, that would correspond to Analog Input 3 being at +24 volts. But your system won't be perfect, so how far away from +24 volts could Analog Input 3 be before it started to become a problem? – EM Fields Apr 29 '16 at 15:48
  • You can also change the +24V connection to +3.3V instead. The values of the resistors obviously has to be recalculated. Potential advantges are: you don't need to bring +24V on-board if it is not already on-board. The +3.3V may have better tolerance or of known tolerance. – rioraxe Apr 29 '16 at 22:12
  • This should still work if you are able to account for the conversion from the (-24,24) to (0,3.3). If you cannot account for the change within the ADC you will not be able to. – StudentJJ Oct 23 '17 at 00:48

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