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16-bits ADC anyone?

Discussion in 'Embedded' started by Bruno Richard, Jun 5, 2007.

  1. Hi all,

    I am working on a project where I need some 16 bits ADC to retrieve
    information from a sensor. I also need a small microcontroller such as
    a PIC, AVR or 8051, and I got surprising quotes for the ADC: Around $5
    (qty 1000), which is 5 times more expensive than the controller!

    Does anyone have an idea about how I can get some low cost ADC-
    Controller solution? I need only few dozens of samples per second, so
    some of you may have nice tricks to do that (op-amps, capacitor charge
    time stuff and the like).

    Thanks, Bruno
     
    Bruno Richard, Jun 5, 2007
    #1
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  2. "Bruno Richard" <> wrote in message
    news:...
    > Hi all,
    >
    > I am working on a project where I need some 16 bits ADC to retrieve
    > information from a sensor. I also need a small microcontroller such as
    > a PIC, AVR or 8051, and I got surprising quotes for the ADC: Around $5
    > (qty 1000), which is 5 times more expensive than the controller!
    >
    > Does anyone have an idea about how I can get some low cost ADC-
    > Controller solution? I need only few dozens of samples per second, so
    > some of you may have nice tricks to do that (op-amps, capacitor charge
    > time stuff and the like).


    You might want to look at sigma-delta type converters. They often offer much
    better than 16 bits at ~100 Hz, and generally cheap.

    Peter
     
    Peter Dickerson, Jun 5, 2007
    #2
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  3. Bruno Richard wrote:
    > Hi all,
    >
    > I am working on a project where I need some 16 bits ADC to retrieve
    > information from a sensor. I also need a small microcontroller such as
    > a PIC, AVR or 8051, and I got surprising quotes for the ADC: Around $5
    > (qty 1000), which is 5 times more expensive than the controller!
    >
    > Does anyone have an idea about how I can get some low cost ADC-
    > Controller solution? I need only few dozens of samples per second, so
    > some of you may have nice tricks to do that (op-amps, capacitor charge
    > time stuff and the like).


    Try something like the Silabs C8051F353R ?
    Shows as $3.48/1500 pcs at Digikey.

    -jg
     
    Jim Granville, Jun 5, 2007
    #3
  4. Bruno Richard

    djordj Guest

    Bruno Richard brought next idea :
    > Hi all,
    >
    > I am working on a project where I need some 16 bits ADC to retrieve
    > information from a sensor. I also need a small microcontroller such as
    > a PIC, AVR or 8051, and I got surprising quotes for the ADC: Around $5
    > (qty 1000), which is 5 times more expensive than the controller!
    >
    > Does anyone have an idea about how I can get some low cost ADC-
    > Controller solution? I need only few dozens of samples per second, so
    > some of you may have nice tricks to do that (op-amps, capacitor charge
    > time stuff and the like).
    >
    > Thanks, Bruno


    Take a look at BB ADS1100 that works 16bit @ 8SPS.
    It has I2C interface (just 3 bytes to retrieve HIGH/LOW word of
    converted value and the status register) and I think it's around 2/3
    euros.

    http://focus.ti.com/docs/prod/folders/print/ads1100.html

    Bye!
     
    djordj, Jun 5, 2007
    #4
  5. On Tue, 05 Jun 2007 08:03:51 -0000, Bruno Richard
    <> wrote:

    >Does anyone have an idea about how I can get some low cost ADC-
    >Controller solution? I need only few dozens of samples per second, so
    >some of you may have nice tricks to do that (op-amps, capacitor charge
    >time stuff and the like).


    The Texas Instruments MSP430 microcontroller has 16 bit ADC on
    chip. In quantity, it should be in the $3 to $5 range depending on
    which version you need. I think Analog Devices has 8051's with 16
    bit ADC. You might also look at Maxim. I seem to recall that they
    have gotten into microcontrollers with high resolution ADCs.
     
    Gary Reichlinger, Jun 5, 2007
    #5
  6. "djordj" <> wrote in message
    news:...
    > Bruno Richard brought next idea :
    >> Hi all,
    >>
    >> I am working on a project where I need some 16 bits ADC to retrieve
    >> information from a sensor. I also need a small microcontroller such
    >> as
    >> a PIC, AVR or 8051, and I got surprising quotes for the ADC: Around
    >> $5
    >> (qty 1000), which is 5 times more expensive than the controller!
    >>
    >> Does anyone have an idea about how I can get some low cost ADC-
    >> Controller solution? I need only few dozens of samples per second, so
    >> some of you may have nice tricks to do that (op-amps, capacitor
    >> charge
    >> time stuff and the like).
    >>
    >> Thanks, Bruno

    >
    > Take a look at BB ADS1100 that works 16bit @ 8SPS.
    > It has I2C interface (just 3 bytes to retrieve HIGH/LOW word of
    > converted value and the status register) and I think it's around 2/3
    > euros.
    >
    > http://focus.ti.com/docs/prod/folders/print/ads1100.html


    Seconded. You certainly want sigma-delta, and you certainly want
    ratiometric. This device does both in a rather nice package.

    Steve
    http://www.fivetrees.com
     
    Steve at fivetrees, Jun 5, 2007
    #6
  7. Bruno Richard

    Guest

    On Jun 5, 3:03 am, Bruno Richard <> wrote:
    > Hi all,
    >
    > I am working on a project where I need some 16 bits ADC to retrieve
    > information from a sensor. I also need a small microcontroller such as
    > a PIC, AVR or 8051, and I got surprising quotes for the ADC: Around $5
    > (qty 1000), which is 5 times more expensive than the controller!


    You might see what you can accomplish by using a cheap micro witha 12-
    bit ADC and a lot of careful filtering (averaging) in software, since
    your needed sample rate is quite low. It might not get you 16 real
    bits, but if unit cost is a driver, figuring out if the accuracy it
    can get you would be enough is probably worth the effort.
     
    , Jun 5, 2007
    #7
  8. Bruno Richard

    antedeluvian Guest

    >On Jun 5, 3:03 am, Bruno Richard <> wrote:
    >> Hi all,
    >>
    >> I am working on a project where I need some 16 bits ADC to retrieve
    >> information from a sensor. I also need a small microcontroller such as
    >> a PIC, AVR or 8051, and I got surprising quotes for the ADC: Around $5
    >> (qty 1000), which is 5 times more expensive than the controller!

    >
    >You might see what you can accomplish by using a cheap micro witha 12-
    >bit ADC and a lot of careful filtering (averaging) in software, since
    >your needed sample rate is quite low. It might not get you 16 real
    >bits, but if unit cost is a driver, figuring out if the accuracy it
    >can get you would be enough is probably worth the effort.
    >
    >
    >


    In this vein, you may want to check the SiLABS application note AN11
    called "IMPROVING ADC RESOLUTION BY OVERSAMPLING AND AVERAGING"
    http://www.silabs.com/public/docume...ntrollers/Precision_Mixed-Signal/en/an118.pdf
     
    antedeluvian, Jun 5, 2007
    #8
  9. Bruno Richard

    Tilmann Reh Guest

    Bruno Richard schrieb:

    > I am working on a project where I need some 16 bits ADC to retrieve
    > information from a sensor. I also need a small microcontroller such as
    > a PIC, AVR or 8051, and I got surprising quotes for the ADC: Around $5
    > (qty 1000), which is 5 times more expensive than the controller!
    >
    > Does anyone have an idea about how I can get some low cost ADC-
    > Controller solution? I need only few dozens of samples per second, so
    > some of you may have nice tricks to do that (op-amps, capacitor charge
    > time stuff and the like).


    You can build a cheap & simple dual slope converter with an external
    reference (like TL431), MUX (4051), integrator and comparator (standard
    OP). With an 8051, you can generate the fixed integration time and
    measure the variable deintegration time with only one of the internal
    timers, while the signal from the comparator provides the timer gate
    signal and the EOC interrupt at the same time.
    (I don't know if other micros also have 16 bit timers with external gate
    signal that also can generate edge triggered interrupts without
    additional pin.)

    With very cheap standard parts, we have made 15 bit ADCs this way. You
    also get line frequency suppression by proper selection of the
    integration time (we tend to use 100 ms to suppress both 50 Hz and 60
    Hz, which gives a total conversion time of 200 ms - or sync it to the
    mains and integrate 16.7 resp. 20 ms), which is often needed for sensor
    signals.

    You can use the other 4051 inputs (or even two or more 4051s) for more
    input channels, which can be converted sequentially. Slow, but reliable.

    Tilmann

    --
    http://www.autometer.de - Elektronik nach Maß.
     
    Tilmann Reh, Jun 5, 2007
    #9
  10. On 2007-06-05, Bruno Richard <> wrote:

    > I am working on a project where I need some 16 bits ADC to retrieve
    > information from a sensor. I also need a small microcontroller such as
    > a PIC, AVR or 8051, and I got surprising quotes for the ADC: Around $5
    > (qty 1000), which is 5 times more expensive than the controller!
    >
    > Does anyone have an idea about how I can get some low cost ADC-
    > Controller solution?


    There are versions of the TI MSP430 that have 16-bit S-D ADCs.

    www.msp430.com

    --
    Grant Edwards grante Yow! I selected E5 ... but
    at I didn't hear "Sam the Sham
    visi.com and the Pharoahs"!
     
    Grant Edwards, Jun 5, 2007
    #10
  11. Bruno Richard

    Thomas Magma Guest

    "Bruno Richard" <> wrote in message
    news:...
    > Hi all,
    >
    > I am working on a project where I need some 16 bits ADC to retrieve
    > information from a sensor. I also need a small microcontroller such as
    > a PIC, AVR or 8051, and I got surprising quotes for the ADC: Around $5
    > (qty 1000), which is 5 times more expensive than the controller!
    >
    > Does anyone have an idea about how I can get some low cost ADC-
    > Controller solution? I need only few dozens of samples per second, so
    > some of you may have nice tricks to do that (op-amps, capacitor charge
    > time stuff and the like).
    >
    > Thanks, Bruno
    >


    How about the AD7143 @ $1.24 for 1000pcs. 43.5 SPS, 3.3mW, 8 channel, 4mm x
    4mm package.

    Thomas
     
    Thomas Magma, Jun 5, 2007
    #11
  12. On Tue, 05 Jun 2007 08:03:51 -0000, Bruno Richard
    <> wrote:

    >I am working on a project where I need some 16 bits ADC to retrieve
    >information from a sensor. I also need a small microcontroller such as
    >a PIC, AVR or 8051, and I got surprising quotes for the ADC: Around $5
    >(qty 1000), which is 5 times more expensive than the controller!


    The problem with microcontrollers with on-chip ADC/DACs is that you
    might not get the nominal 98 dB SNR due to the noise from the
    controller.

    Is DC accuracy (drifts) important in your application ?

    Is this ADC part of a control loop, in which case it would be
    preferable that the ADC is monotonous.

    Paul
     
    Paul Keinanen, Jun 5, 2007
    #12
  13. Paul Keinanen wrote:


    >>I am working on a project where I need some 16 bits ADC to retrieve
    >>information from a sensor. I also need a small microcontroller such as
    >>a PIC, AVR or 8051, and I got surprising quotes for the ADC: Around $5
    >>(qty 1000), which is 5 times more expensive than the controller!

    >
    >
    > The problem with microcontrollers with on-chip ADC/DACs is that you
    > might not get the nominal 98 dB SNR due to the noise from the
    > controller.


    Besides, the high performance ADCs and the microcontrollers are the two
    different technologies. The MCUs with the good ADC/DACs usually contain
    two separate dies in one package. For that reason they are more
    expensive then the equvalent micro + equvalent ADC/DAC.

    >
    > Is DC accuracy (drifts) important in your application ?
    >
    > Is this ADC part of a control loop, in which case it would be
    > preferable that the ADC is monotonous.


    I am wondering of what could be a sensor which requires the ADC with the
    true 16-bit accuracy. For the sensor application, that sounds
    unreasonable to me. Especially considering that the rest of application
    is handled by a small micro. Apparently there is a problem with the
    concept.


    Vladimir Vassilevsky

    DSP and Mixed Signal Design Consultant

    http://www.abvolt.com
     
    Vladimir Vassilevsky, Jun 5, 2007
    #13
  14. On Wed, 06 Jun 2007 00:28:50 +0300, the renowned Paul Keinanen
    <> wrote:

    >On Tue, 05 Jun 2007 08:03:51 -0000, Bruno Richard
    ><> wrote:
    >
    >>I am working on a project where I need some 16 bits ADC to retrieve
    >>information from a sensor. I also need a small microcontroller such as
    >>a PIC, AVR or 8051, and I got surprising quotes for the ADC: Around $5
    >>(qty 1000), which is 5 times more expensive than the controller!

    >
    >The problem with microcontrollers with on-chip ADC/DACs is that you
    >might not get the nominal 98 dB SNR due to the noise from the
    >controller.


    >Is DC accuracy (drifts) important in your application ?
    >
    >Is this ADC part of a control loop, in which case it would be
    >preferable that the ADC is monotonous.
    >
    >Paul


    ITYM "monotonic"-- did a spell chequer get you? ;-)

    Making a slope-type ADC with ~16 bit resolution isn't all that hard,
    nor is adding some dither and oversampling with a successive-
    approximation type converter.


    Best regards,
    Spehro Pefhany
    --
    "it's the network..." "The Journey is the reward"
    Info for manufacturers: http://www.trexon.com
    Embedded software/hardware/analog Info for designers: http://www.speff.com
     
    Spehro Pefhany, Jun 6, 2007
    #14
  15. On Wed, 06 Jun 2007 00:28:50 +0300, Paul Keinanen <>
    wrote:

    >The problem with microcontrollers with on-chip ADC/DACs is that you
    >might not get the nominal 98 dB SNR due to the noise from the
    >controller.


    Some of the newer microcontrollers such as the MSP430 get around
    this problem by using very low power operation. Others take their
    samples while the microcontroller is in sleep mode.
     
    Gary Reichlinger, Jun 6, 2007
    #15
  16. Bruno Richard

    mw Guest

    Vladimir Vassilevsky wrote:
    > I am wondering of what could be a sensor which requires the ADC with the
    > true 16-bit accuracy. For the sensor application, that sounds
    > unreasonable to me. Especially considering that the rest of application
    > is handled by a small micro. Apparently there is a problem with the
    > concept.


    Plenty of sensors are read with 16-bit ADCs. Examples: pressure sensor,
    strain gauge, position sensors, etc. Just take a look at the Analog
    Devices app notes.
     
    mw, Jun 6, 2007
    #16
  17. On 2007-06-06, mw <> wrote:
    > Vladimir Vassilevsky wrote:


    >> I am wondering of what could be a sensor which requires the
    >> ADC with the true 16-bit accuracy.


    Plenty of them.

    >> For the sensor application, that sounds unreasonable to me.
    >> Especially considering that the rest of application is handled
    >> by a small micro. Apparently there is a problem with the
    >> concept.

    >
    > Plenty of sensors are read with 16-bit ADCs. Examples: pressure sensor,
    > strain gauge, position sensors, etc. Just take a look at the Analog
    > Devices app notes.


    I know of quite a few applications that are using 20 and 24 bit
    ADCs. 16 bits really isn't pushing the limits at all.

    --
    Grant Edwards grante Yow! hubub, hubub, HUBUB,
    at hubub, hubub, hubub, HUBUB,
    visi.com hubub, hubub, hubub.
     
    Grant Edwards, Jun 6, 2007
    #17
  18. On Wed, 06 Jun 2007 04:32:35 -0000, the renowned Grant Edwards
    <> wrote:

    >On 2007-06-06, mw <> wrote:
    >> Vladimir Vassilevsky wrote:

    >
    >>> I am wondering of what could be a sensor which requires the
    >>> ADC with the true 16-bit accuracy.

    >
    >Plenty of them.
    >
    >>> For the sensor application, that sounds unreasonable to me.
    >>> Especially considering that the rest of application is handled
    >>> by a small micro. Apparently there is a problem with the
    >>> concept.

    >>
    >> Plenty of sensors are read with 16-bit ADCs. Examples: pressure sensor,
    >> strain gauge, position sensors, etc. Just take a look at the Analog
    >> Devices app notes.

    >
    >I know of quite a few applications that are using 20 and 24 bit
    >ADCs. 16 bits really isn't pushing the limits at all.


    Anyway, he didn't specify what the accuracy was. 16 bit resolution is
    pretty unremarkable for control applications.


    Best regards,
    Spehro Pefhany
    --
    "it's the network..." "The Journey is the reward"
    Info for manufacturers: http://www.trexon.com
    Embedded software/hardware/analog Info for designers: http://www.speff.com
     
    Spehro Pefhany, Jun 6, 2007
    #18
  19. "CBFalconer" <> wrote in message
    news:...
    > mw wrote:
    >> Vladimir Vassilevsky wrote:
    >>
    >>> I am wondering of what could be a sensor which requires the ADC
    >>> with the true 16-bit accuracy. For the sensor application, that
    >>> sounds unreasonable to me. Especially considering that the rest
    >>> of application is handled by a small micro. Apparently there is
    >>> a problem with the concept.

    >>
    >> Plenty of sensors are read with 16-bit ADCs. Examples: pressure
    >> sensor, strain gauge, position sensors, etc. Just take a look
    >> at the Analog Devices app notes.

    >
    > Yes, but the question is why? That gives a result to 1 part in
    > 65535 over the range, and even if we assign the high order bit to
    > allow overruns by a factor of 2, it is still 1 part in 32767. I
    > find such precision requirements to be extremely rare.


    I'm use to processing photosensor data. Photodiodes can be linear over a
    huge dynamic range - I was told 14 decades but I've only tried six. I
    typically want 10-bit accuracy, so some of this can be handled with a gain
    switch.

    I've processed temperature sensor data with 0.001°C resolution (but less
    accuracy), required for good closed loop performance.

    Audio data is another that needs good linearity but can tolerate scale
    errors.

    But I would help if the OP explained what he wanted the ADC for so that we
    can assess what aspects of the system require 16-bitness.

    --
    Peter
     
    Peter Dickerson, Jun 6, 2007
    #19
  20. mw wrote:

    > Vladimir Vassilevsky wrote:
    >
    >> I am wondering of what could be a sensor which requires the ADC with
    >> the true 16-bit accuracy. For the sensor application, that sounds
    >> unreasonable to me. Especially considering that the rest of
    >> application is handled by a small micro. Apparently there is a problem
    >> with the concept.

    >
    >
    > Plenty of sensors are read with 16-bit ADCs. Examples: pressure sensor,
    > strain gauge, position sensors, etc.


    And there is absolutely no need for the 16 bit accuracy in all of those
    cases, because the sensors are only accurate to somewhat 0.1% at the
    very best. All that required is a 10-bit ADC with the proper gain and
    offset.

    > Just take a look at the Analog
    > Devices app notes.


    If I was making the 100bit ADCs, I am sure I would recommend a 100bit ADC.

    Vladimir Vassilevsky

    DSP and Mixed Signal Design Consultant

    http://www.abvolt.com
     
    Vladimir Vassilevsky, Jun 6, 2007
    #20
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