16-bits ADC anyone?

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" <> wrote in message
news: ups.com...
> 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

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

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/folder...t/ads1100.html

Bye!

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.

"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/folder...t/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

On Jun 5, 3:03 am, Bruno Richard <bruno.richard...@gmail.com> 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.

>On Jun 5, 3:03 am, Bruno Richard <bruno.richard...@gmail.com> 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/documen...l/en/an118.pdf

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.

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

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