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Turning 20V max into 5V max

Discussion in 'General Electronics Discussion' started by patr0805, Apr 26, 2010.

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  1. patr0805


    Apr 26, 2010
    Okay I have a microcontroller and I want to messure the amount of voltage thorgh one of the analog inputs, now I have to make 20V max into the max analog input which is 5V.
    (the 20V is not from the powersource that gives the microcontroller 5V)

    I know I can put resistors and stuff, but my problem is that in order for the circuit to messure the input from another system, it has to merge together with the other circuit' s powersource.

    I can' t just merge - and + together on the circuits because then the microcontroller would be overpowered and break.

    20V -><- 5V = 25V

    Any ideas.
  2. NickS


    Apr 6, 2010
    At first I thought you were just trying to divide down an analog signal from +20V to +5V. But then you talk about merging power sources(why).

    Treat your uC circuit as one entity(+5VDC max)

    The signal source is a separate entity(+20VDC max)
    You do not have to merge the systems main powers together to read the 20v signal on the 5v board but you do have to divide down the signal you want to measure. You can use a basic voltage divider("resistors and stuff" minus the stuff) to reduce the 20V signal into a safe range for the uC.
  3. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    Jan 21, 2010
    Well, you were not too clear on your problem.

    All I can add to the earlier comments are:

    1) do the 20V and 5V rails share a common ground (or can they?)
    2) is the voltage to be measured referenced to ground?
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