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Voltage Divider with the MAX186 — Parallax Forums

Voltage Divider with the MAX186

ArchiverArchiver Posts: 46,084
edited 2003-02-27 16:40 in General Discussion
I am trying to use a voltage divider with the MAX186 ADC to read a 9 volt
source. I know I have to factor in the load of the MAX186 so I can get the
proper resistors for the voltage divider but I can not find what this load is.
Does anyone know where I can find this so I can figure out what resistors to
use?

Thanks!

Hank

Comments

  • ArchiverArchiver Posts: 46,084
    edited 2003-02-27 01:32
    I am trying to use a voltage divider with the MAX186 ADC to read a 7
    volt source. I know I have to factor in the load of the MAX186 so I
    can get the proper resistors for the voltage divider but I can not
    find what this load is. Does anyone know where I can find this so I
    can figure out what resistors to use?

    Thanks!

    Hank
  • ArchiverArchiver Posts: 46,084
    edited 2003-02-27 01:47
    http://pdfserv.maxim-ic.com/arpdf/MAX186-MAX188.pdf

    I would think the load for the chip would be negligible. Since it has a
    4.096 volt internal reverence, your voltage divider needs to drop about 3
    volts. Best thing to do is calculate using standard resistor values -- you
    can get pretty close that way and not have to tweak anything.
    Original Message

    > I am trying to use a voltage divider with the MAX186 ADC to read a 7
    > volt source. I know I have to factor in the load of the MAX186 so I
    > can get the proper resistors for the voltage divider but I can not
    > find what this load is. Does anyone know where I can find this so I
    > can figure out what resistors to use?
  • ArchiverArchiver Posts: 46,084
    edited 2003-02-27 02:05
    I am using 2 10K ohm resistors for the voltage divider. The battery voltage I am
    trying to measure is putting out 7.93 volts. The voltage at the junction of the
    voltage divider reads 3.96 volts. I measured the resistors and they are within
    1% of each other. Ideas?

    Hank

    Original Message
    From: "Rodent" <daweasel@s...>
    To: <basicstamps@yahoogroups.com>
    Sent: Wednesday, February 26, 2003 8:47 PM
    Subject: Re: [noparse][[/noparse]basicstamps] Voltage Divider with the MAX186


    > http://pdfserv.maxim-ic.com/arpdf/MAX186-MAX188.pdf
    >
    > I would think the load for the chip would be negligible. Since it has a
    > 4.096 volt internal reverence, your voltage divider needs to drop about 3
    > volts. Best thing to do is calculate using standard resistor values -- you
    > can get pretty close that way and not have to tweak anything.
    >
    >
    Original Message
    >
    > > I am trying to use a voltage divider with the MAX186 ADC to read a 7
    > > volt source. I know I have to factor in the load of the MAX186 so I
    > > can get the proper resistors for the voltage divider but I can not
    > > find what this load is. Does anyone know where I can find this so I
    > > can figure out what resistors to use?
    >
    >
    >
    >
    > To UNSUBSCRIBE, just send mail to:
    > basicstamps-unsubscribe@yahoogroups.com
    > from the same email address that you subscribed. Text in the Subject and Body
    of the message will be ignored.
    >
    >
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  • ArchiverArchiver Posts: 46,084
    edited 2003-02-27 03:06
    It should work, assuming you are talking to the chip correctly. I just
    worked through a similar deal to make a battery gauge with a small Atmel
    processor with onboard ADC. If you haven't worked with ADC's before, the
    trick may be to start with a less complicated part. Here is some stuff from
    Parallax on one of their student lessons:

    http://www.parallax.com/Downloads/Documentation/edu/Basic_Analog_and_Digital
    _V_1.0.pdf
    Original Message

    > I am using 2 10K ohm resistors for the voltage divider. The battery
    voltage I am trying to measure is putting out 7.93 volts. The voltage at the
    junction of the voltage divider reads 3.96 volts. I measured the resistors
    and they are within 1% of each other. Ideas?

    >
    Original Message

    > > http://pdfserv.maxim-ic.com/arpdf/MAX186-MAX188.pdf
    > >
    > > I would think the load for the chip would be negligible. Since it has a
    > > 4.096 volt internal reverence, your voltage divider needs to drop about
    3
    > > volts. Best thing to do is calculate using standard resistor values --
    you
    > > can get pretty close that way and not have to tweak anything.
    > >
    > >
    Original Message
    > >
    > > > I am trying to use a voltage divider with the MAX186 ADC to read a 7
    > > > volt source. I know I have to factor in the load of the MAX186 so I
    > > > can get the proper resistors for the voltage divider but I can not
    > > > find what this load is. Does anyone know where I can find this so I
    > > > can figure out what resistors to use?
  • ArchiverArchiver Posts: 46,084
    edited 2003-02-27 08:01
    --- In basicstamps@yahoogroups.com, "Hank Hagquist" <hankster@h...>
    wrote:
    > I am using 2 10K ohm resistors for the voltage divider. The battery
    voltage I am trying to measure is putting out 7.93 volts. The voltage
    at the junction of the voltage divider reads 3.96 volts. I measured
    the resistors and they are within 1% of each other. Ideas?
    >

    Sounds perfectly ok, what is your problem? May be 3.96V is yet to
    close to 4.096V, so change one of your 10k resistrs to something
    close to 5k to get 9V*5k/(5k+10k) = 3V. or use 20k/10k to reduce
    the load even more.

    Regards
    Adrian
  • ArchiverArchiver Posts: 46,084
    edited 2003-02-27 13:47
    I think maybe I've been sitting at the bench too long... [noparse]:)[/noparse] Yes, the voltage was
    right but my math was wrong on the programming and the numbers were not coming
    out correct... argggg!

    Sorry for the dumb question.

    Hank

    Original Message
    From: <adrian.schneider@t...>
    To: <basicstamps@yahoogroups.com>
    Sent: Thursday, February 27, 2003 3:01 AM
    Subject: [noparse][[/noparse]basicstamps] Re: Voltage Divider with the MAX186


    > --- In basicstamps@yahoogroups.com, "Hank Hagquist" <hankster@h...>
    > wrote:
    > > I am using 2 10K ohm resistors for the voltage divider. The battery
    > voltage I am trying to measure is putting out 7.93 volts. The voltage
    > at the junction of the voltage divider reads 3.96 volts. I measured
    > the resistors and they are within 1% of each other. Ideas?
    > >
    >
    > Sounds perfectly ok, what is your problem? May be 3.96V is yet to
    > close to 4.096V, so change one of your 10k resistrs to something
    > close to 5k to get 9V*5k/(5k+10k) = 3V. or use 20k/10k to reduce
    > the load even more.
    >
    > Regards
    > Adrian
    >
    >
    > To UNSUBSCRIBE, just send mail to:
    > basicstamps-unsubscribe@yahoogroups.com
    > from the same email address that you subscribed. Text in the Subject and Body
    of the message will be ignored.
    >
    >
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    >
  • ArchiverArchiver Posts: 46,084
    edited 2003-02-27 13:58
    Thanks for your reply.
    I does work, the problem is the voltage regulator is
    heating up and get damaged after sometime.
    I am wondering what is causing it to draw high current
    when using 12 inputs and one output.

    Regards,
    Napoleon

    --- Rodent <daweasel@s...> wrote:
    > It should work, assuming you are talking to the chip
    > correctly. I just
    > worked through a similar deal to make a battery
    > gauge with a small Atmel
    > processor with onboard ADC. If you haven't worked
    > with ADC's before, the
    > trick may be to start with a less complicated part.
    > Here is some stuff from
    > Parallax on one of their student lessons:
    >
    >
    http://www.parallax.com/Downloads/Documentation/edu/Basic_Analog_and_Digital
    > _V_1.0.pdf
    >
    >
    Original Message
    >
    > > I am using 2 10K ohm resistors for the voltage
    > divider. The battery
    > voltage I am trying to measure is putting out 7.93
    > volts. The voltage at the
    > junction of the voltage divider reads 3.96 volts. I
    > measured the resistors
    > and they are within 1% of each other. Ideas?
    >
    > >
    Original Message
    >
    > > >
    > http://pdfserv.maxim-ic.com/arpdf/MAX186-MAX188.pdf
    > > >
    > > > I would think the load for the chip would be
    > negligible. Since it has a
    > > > 4.096 volt internal reverence, your voltage
    > divider needs to drop about
    > 3
    > > > volts. Best thing to do is calculate using
    > standard resistor values --
    > you
    > > > can get pretty close that way and not have to
    > tweak anything.
    > > >
    > > >
    Original Message
    > > >
    > > > > I am trying to use a voltage divider with the
    > MAX186 ADC to read a 7
    > > > > volt source. I know I have to factor in the
    > load of the MAX186 so I
    > > > > can get the proper resistors for the voltage
    > divider but I can not
    > > > > find what this load is. Does anyone know where
    > I can find this so I
    > > > > can figure out what resistors to use?
    >
    >
    >
    >
    > To UNSUBSCRIBE, just send mail to:
    > basicstamps-unsubscribe@yahoogroups.com
    > from the same email address that you subscribed.
    > Text in the Subject and Body of the message will be
    > ignored.
    >
    >
    > Your use of Yahoo! Groups is subject to
    > http://docs.yahoo.com/info/terms/
    >
    >


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  • ArchiverArchiver Posts: 46,084
    edited 2003-02-27 16:40
    It seems as if the circuit is drawing excessive current. let's assume your
    voltage regulator is rated 1 amp at
    5VDC. That is 5 watts max.
    The problem probably isn't the one output as that would damage the stamp too.
    So maybe the problem is related to the wiring related to the inputs. What size
    (ohmic value) resistors are you
    using as pull ups for the inputs? 10k or larger would work.
    12 10k resistors all drawing current at the same time from a 5V source is only
    .03 watts if all is normal.
    Are you sure they are all the correct value? A 1k or 100 ohm didn't sneak in
    there by mistake?

    To trouble shoot:
    1. Disconnect the inputs and the outputs.
    2. Put a 1 ohm 10 watt resistor in series with the output of the voltage
    regulator. Use a voltmeter to monitor
    the voltage across this series resistor. Each volt across it means 1 amp of
    current. I=V/R I= 1V/1 ohm = 1amp
    3. Connect inputs one at a time and observe the voltmeter. Each input in the on
    (current drawing) position show
    only increase the voltage by .0005V.
    4. Keep hooking things up until you find the problem.

    Good luck
    Fred










    napoleon shlimon wrote:

    > Thanks for your reply.
    > I does work, the problem is the voltage regulator is
    > heating up and get damaged after sometime.
    > I am wondering what is causing it to draw high current
    > when using 12 inputs and one output.
    >
    > Regards,
    > Napoleon
    >
    > --- Rodent <daweasel@s...> wrote:
    > > It should work, assuming you are talking to the chip
    > > correctly. I just
    > > worked through a similar deal to make a battery
    > > gauge with a small Atmel
    > > processor with onboard ADC. If you haven't worked
    > > with ADC's before, the
    > > trick may be to start with a less complicated part.
    > > Here is some stuff from
    > > Parallax on one of their student lessons:
    > >
    > >
    > http://www.parallax.com/Downloads/Documentation/edu/Basic_Analog_and_Digital
    > > _V_1.0.pdf
    > >
    > >
    Original Message
    > >
    > > > I am using 2 10K ohm resistors for the voltage
    > > divider. The battery
    > > voltage I am trying to measure is putting out 7.93
    > > volts. The voltage at the
    > > junction of the voltage divider reads 3.96 volts. I
    > > measured the resistors
    > > and they are within 1% of each other. Ideas?
    > >
    > > >
    Original Message
    > >
    > > > >
    > > http://pdfserv.maxim-ic.com/arpdf/MAX186-MAX188.pdf
    > > > >
    > > > > I would think the load for the chip would be
    > > negligible. Since it has a
    > > > > 4.096 volt internal reverence, your voltage
    > > divider needs to drop about
    > > 3
    > > > > volts. Best thing to do is calculate using
    > > standard resistor values --
    > > you
    > > > > can get pretty close that way and not have to
    > > tweak anything.
    > > > >
    > > > >
    Original Message
    > > > >
    > > > > > I am trying to use a voltage divider with the
    > > MAX186 ADC to read a 7
    > > > > > volt source. I know I have to factor in the
    > > load of the MAX186 so I
    > > > > > can get the proper resistors for the voltage
    > > divider but I can not
    > > > > > find what this load is. Does anyone know where
    > > I can find this so I
    > > > > > can figure out what resistors to use?
    > >
    > >
    > >
    > >
    > > To UNSUBSCRIBE, just send mail to:
    > > basicstamps-unsubscribe@yahoogroups.com
    > > from the same email address that you subscribed.
    > > Text in the Subject and Body of the message will be
    > > ignored.
    > >
    > >
    > > Your use of Yahoo! Groups is subject to
    > > http://docs.yahoo.com/info/terms/
    > >
    > >
    >
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