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PICList Thread
'ADC+DAC'
1997\06\03@091046 by Antonio Almeida

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Does anyone know of a chip with a DAC and a ADC ?

TIA,
Antonio Almeida

1997\06\03@095707 by Clyde Smith-Stubbs

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On Tue, Jun 03, 1997 at 02:10:07PM +0000, Antonio Almeida wrote:
> Does anyone know of a chip with a DAC and a ADC ?

Depends on what kind of DAC you want. There are plenty of chips around
with ADCs and PWM outputs, which provide a digital-to-analog function,
albeit with trade-offs between resolution and speed.

True DACs are rarer, but the PIC14000 has two 8 bit DACs, plus an 8 channel
ADC (slope conversion, though, not successive approximation).

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1997\06\03@105229 by Keith Dowsett

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At 14:10 03/06/97 +0000, you wrote:
>Does anyone know of a chip with a DAC and a ADC ?
>
>TIA,
>Antonio Almeida

What do you need to do? For fairly slowly changing outputs you can use a 16C73
It has an 8-bit ADC and PWM. Add a capacitor,resistor, and op-amp to convert
from time to volts for your DAC.

Some more clues about your application might get some better answers.

Bye for now,

Keith.




==========================================================
Keith Dowsett         "Variables won't; constants aren't."

E-mail: .....kdowsettKILLspamspam@spam@rpms.ac.uk
  WWW: http://kd.rpms.ac.uk/index.htm

1997\06\03@152930 by Antonio Almeida

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On Tue, 3 Jun 1997, Keith Dowsett wrote:

> At 14:10 03/06/97 +0000, you wrote:
> >Does anyone know of a chip with a DAC and a ADC ?
> >
> >TIA,
> >Antonio Almeida
>
> What do you need to do? For fairly slowly changing outputs you can use a 16C73
> It has an 8-bit ADC and PWM. Add a capacitor,resistor, and op-amp to convert
> from time to volts for your DAC.
>
> Some more clues about your application might get some better answers.
>
> Bye for now,
>
> Keith.

Maybe this can solve my problem, i need the ADC and a couple of op-amp to
convert current change, in a line, to data. The DAC is used to subtract
the idle current in the line. Maybe this is a little confusing.
The speed of the DAC isn't very important but it needs to be very stable,
the PWM and the integrator can do that ?

Antonio Almeida

1997\06\04@020607 by nigelg

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In message  <Pine.OSF.3.96.970603190842.24670B-100000spamKILLspamtom.fe.up.pt>> .....PICLISTKILLspamspam.....MITVMA.MIT.EDU writes:

> Maybe this can solve my problem, i need the ADC and a couple of op-amp to
> convert current change, in a line, to data. The DAC is used to subtract
> the idle current in the line. Maybe this is a little confusing.
> The speed of the DAC isn't very important but it needs to be very stable,
> the PWM and the integrator can do that ?

I can't comment on the particular PWM in the PIC, but this filtered PWM
is commonly used for the tuning circuits in almost all modern TV's.

The PWM output from the processor is fed via a resistor to the base of an
NPN transistor, the collector of which goes via a resistor to a special
33 volt 'super zener' usually a ZTK33B. This generates a 33 volt squarewave
on the collector of the transistor, the amplitude of which is very stable
as these ZTK's are very good. From the collector it's fed via two or three
stages of low-pass filtering (just series resistors and capacitors to ground)
and on to the tuning pin of the tuner.

I've had meter's and scope's on these tuning rails many times, and the
voltage on the tuning pin is remarkably stable and has no visible ripple.
Even with the AFC turned off, the voltage remains constant during my full
working day.

As long as have a suitable stable HT, you should be OK.

Nigel.

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1997\06\04@043356 by Keith Dowsett

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Sounds feasible to me. I'm just not sure if it's the best solution to your
problem. I was wondering if you could use a FET to charge a capacitor when
the line is idle and use that as a the reference for a comparator.

I'll try and sketch it but no promises...



                                                   0V
                                                   |
          |           |--/\/\/--|                 <
          |           |         |                  >
          |-----/\/\/---|\      |        Diode    <
          >             | \     |           .     |
 r(sense)<              |  \____|___________|\|___|__|\
          >             |  /        |       |/|      | \
         <              | /         |       '        |  \_____P2
          |----/\/\/----|/          -|               |  /
          |                          |<---P1   ______| /
          |                         -|         |     |/
          |                         |__________|
                                    |
                                    |
                                  -----
                                  -----
                                    |
                                   0V

I hope that's right. When the op-amp output exceeds V(ref) by 0.7 volts (1
diode drop) your data has arrived so switch off the FET and start sampling.
When the line is low, turn the FET on to maintain the voltage on the capacitor.

Requires 2 pins, a FET and a dual FET input op-amp.

Hope this is some help. I'm not too hot on analog design so perhaps someone
on the list can simplify it a bit. I can't help thinking that a simple
analog filter should be able to do the same job without a FET.

Keith.
==========================================================
Keith Dowsett         "Variables won't; constants aren't."

E-mail: kdowsettspamspam_OUTrpms.ac.uk
  WWW: http://kd.rpms.ac.uk/index.htm

1997\06\04@092058 by cbecerra

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Antonio Almeida wrote:
>
> Does anyone know of a chip with a DAC and a ADC ?
>
> TIA,
> Antonio Almeida


Try Philips, they have a chip with an A/D, D/A and I2C bus, If you can't
find it let me know and I'll do a search.
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