There is a digital chip called a 'priority encoder' which will take 2**N
digital inputs and return an N bit code identifying which is the 'highest
priority' one that is active (or a special output if none is active).

The 74LS348  (I assume an HC equivalent exists) takes 8 active low inputs
and encodes them to 3 outputs.

The chips support cascading so you can build a network of them that will
directly decode your 50 input lines to a 6-bit binary number.

The first level of the network contains 7 chips which provide 56 inputs. You
only use 50 of them.

The second level of the network contains 1 more chip, the inputs of which
are connected to cascade outputs from the first level chips.

The first level chips provide the low-order 3 bits of the resulting binary
value.

The second level chip providews the high-order 3 bits of the 6-bit value.

You can then use that 6-bit binary number to drive a D/A chip.

No PIC needed.

Bob Ammerman
RAm Systems
(contract development of high performance, high function, low-level
software)


----- Original Message -----
From: "Douglas Butler" <dbutler@IMETRIX.COM>
To: <PICLIST@MITVMA.MIT.EDU>
Sent: Thursday, August 30, 2001 9:07 AM
Subject: Re: PIC UNUSUAL D/A APPLICATION


> My first thought would not be to use a processor at all.  I would run
> the 50 inputs to 50 open collector buffers pulling down a resistor
> network.  Something like a R2R network but it might be simpler as you
> don't have to distinguish when multiple lines are low together.  Finally
> use an op amp to buffer and filter the output.
>
> Sherpa Doug
>
> > -----Original Message-----
> > From: tim [mailto:stm800@CITY-NET.COM]
> > Sent: Wednesday, August 29, 2001 8:37 PM
> > To: PICLIST@MITVMA.MIT.EDU
> > Subject: PIC UNUSUAL D/A APPLICATION
> >
> >
> > I have 50 seperate logic lines  that switch in sequence from
> > # 1 to # 50 then reverse from # 50 to # 1
> > at any one time only one line is in a low state  and all
> > others are high state. what I need is an analog output
> > voltage generated from the pic in response to which switched
> > line is enabled.
> > example:
> >
> >  max reference voltage output is 1 volt at line 50 switched on.
> >  half of the reference voltage is 500 mv at line 25 switched on.
> >  each switched line represents a 20 mv  change in output voltage.
> >
> >  these parameters are not set in stone and the analog
> > reference voltage could
> > change if it made code and chip selection easier.
> >
> > any thoughts on which pic chip to use  as i have not bought
> > any chips yet.
> > is there a simple  mixed signal  or  d/a chip that will do
> > this instead of using a pic chip?
> > it seems that this type of digital line switching (single
> > line enabled only )
> > to generate an analog voltage is really not what the D/A
> > chips do that are
> > presently out there on the market. well as easy as this
> > application seems to be
> >  i want to ask before  i begin  re-inventing  sliced bread....
> >
> > thanks alot  for reading this and all comments and
> > suggestions welcome         tims 800
> >
> >
> >
> > --
> > http://www.piclist.com hint: To leave the PICList
> > mailto:piclist-unsubscribe-request@mitvma.mit.edu
> >
> >
>
> --
> http://www.piclist.com hint: PICList Posts must start with ONE topic:
> [PIC]:,[SX]:,[AVR]: ->uP ONLY! [EE]:,[OT]: ->Other [BUY]:,[AD]: ->Ads
>
>

--
http://www.piclist.com hint: PICList Posts must start with ONE topic:
[PIC]:,[SX]:,[AVR]: ->uP ONLY! [EE]:,[OT]: ->Other [BUY]:,[AD]: ->Ads