F/V as a DAC

[Bissell, Harry]

Frequency to Voltage converters make a very reasonable but slow DAC. Major
advantages are that the output is a serial stream (i.e. 1 bit wide), so you
can get signal isolation very cheap (opto, xfmr, etc). You can offset the
frequency so that a non-zero frequency can represent a DC level, or even
take bipolar inputs. The output of a F/V can be recorded easily (with
scaling) on analog magnetic tape. Integration is as easy as a digital
counter, with abolutely no droop or drift. Sounds Great ???    Did you want
your data by next week ???    ;-) Harry Bissell

> -----Original Message-----
> From:	Fraser, Colin J [SMTP:Colin.Fraser at scottishpower.plc.uk]
> Sent:	Tuesday, March 09, 1999 8:45 AM
> To:	'inman at interpath.com'; synth-diy at mailhost.bpa.nl
> Subject:	RE: A Few Simple Questions
> 
> > -----Original Message-----
> > From: inman at interpath.com [mailto:inman at interpath.com]
> > Sent: 09 March 1999 15:48
> > To: synth-diy at mailhost.bpa.nl
> > Subject: A Few Simple Questions
> > 
> > 
> > Would someone please define these terms / answer these questions?
> > 
> > Rail to Rail
> > Does that mean possible output voltage goes from ground to V+?
> 
> If you have a single rail supply it does. 
> Usually, op-amp based circuits have a dual rail supply - ie, there are two
> power supply outputs at a positive and a negative voltage, usually +/- 12
> or
> 15 volts. There will be a ground (0 volt) line as well as a reference.
> Most op-amps will not manage to drive their output voltage all the way to
> the voltage at either the positive or negative supply.
> Some don't even like their inputs driven all the way to the supply rails.
> 
> > What does it mean to say an AD/DA converter is 2 or 4 or 8 channels?
> > Are these inputs summed in the output or sent in parallel?
> 
> Multi-channel converters will either have more than one converter on the
> chip, or they will have a built in multiplexer or demultiplexer - that's
> just a multiway switch that can select different inputs or outputs for the
> ADC/DAC to connect to. A multichannel DAC with a demultiplexer may also
> need
> a circuit to store the output voltage when the DAC is not switched to that
> output channel. 
> 
> > Is there a simple 8-bit DAC with parallel in?  Is there an 8-bit DAC
> > for dummies?  Colin said he had had great success making a DAC with a
> > chip.  Colin -- which one?
> 
> There are several - I have used ZN558 and ZN428.
> Given that there are inexpensive 12 bit DACs about, you may be just as
> well
> to use one of these. Burr Brown make a nice 12 bit DAC that has an 8 bit
> parallel input and a register select line, so you write the lower 8 bits,
> then the upper 4 bits. There are several others that work like this.
> With a look up table in ROM, you can use one of these to give a linear
> (Hz/v) output.
> Many of the 12 and 16 bit converters have serial inputs, but there is
> plenty
> of documentation on the web showing how to use these.
> Some DACs are designed more for outputing digital audio than contant
> voltages tho'.
> 
> > Any comments on frequency to voltage converters?  Not for tracking a
> > musical note, but used more as a DAC?  They clearly have some error
> > and tracking times are a concern?  Were these the DAC of the past?
> 
> Never used/built one...
> 
> Colin f