wb lcd display

Tue Sep 11 02:33:46 GMT 2001

Hi Bill

I have an Excel spreadsheet that I have been working on.  If you use a 3.2
volt reference for the A2D (10bit) you will get 16 counts for each .05 volts
input, 4 if you only use 8 bits of the A2D.  I would divide the 8 bit value
by 4 (save the "remainder" for later) and then look up a value in a table
(value A).   You could then interpolate to a closer value.  To interpolate
then look up the next higher entry in the table (value A+1), subtract value
A from value A+1 and divide the result by 4.  This gives you value of each
count on the A2D.  Fine tune the reading by adding this back to value A
"remainder" times.  This is probably as clear as mud,  if I get time I will
code it for a PIC.

I am a little concerned about the A2D lines getting zapped with static.  I
would add 100 ohm resistors in series with .1uF to ground (as close to the
PIC as possible).  The cap will also help supply the current to the A2D in
case the input impedance is a bit high.  Either Microchip or TI have an app
note on using capacitive input SA converters, they recommend a cap on the
input.  If you use an external reference you will need to use RA3 for the
reference and move the fourth A2D to RA4 or RA5

Dave Mumert

----- Original Message -----
From: "Bill Shaw" <bshaw at connix.com>
To: <gmecm at diy-efi.org>
Sent: Monday, September 10, 2001 6:29 PM
Subject: Re: wb lcd display

> Thanks for the replies guys.
>
> I think I'm OK with the PS section now.  After I sent the schematic I
remembered a
> bunch of protection in the EFI332 schematic similar to what Bob and Eric
> recommended. I'll implement something like that,  with a LM2931 regulator.
The
> ferrites will be deleted,  leftovers from the low-power fcc-able design it
was
> stolen from.
>
> Darrel: Yes,  please do upload the PDF version.
>
> Marc:  50 ma should be far more than it will ever need.  The Orcad (V9)
file is in
> incoming also - WB_LCD.DSN.
>
> I'll update the schematic and post an announcement when I do.  In the mean
time,
> I'm looking for constructive feedback on the design.
>
> I have code I'm going to steal for the LCD, A/D converter,  data logging
to
> eeprom,  and serial monitor.  The boot loader sounds good,  I'll look into
that
> also.
>
> I don't have the data for the translation table.  I saw some formulas
floating
> about recently,  has anyone plugged them onto a spreadsheet to generate
some
> numbers yet?
>
> Regards,
>
> Bill
>
>
> > Date: Mon, 10 Sep 2001 08:07:28 -0400
> > From: "rr" <rrauscher at nni.com>
> > Subject: Re: wb lcd display
> >
> > For the 12 -> 5v p/s, I would do something close to how
> > the WB UEGO circuit is powered. Just change the 78L08
> > out for a run-of-the-mill 7805 regulator chip. Maybe add
> > a 1N4001 diode in series with the input.
> >
> > I'm going to try to look at the schematic. However I don't
> > know how much luck I'll have with the EPS file.
> >
> > BobR.
> >
> > ----
>
> >
> > Date: Mon, 10 Sep 2001 11:19:48 -0400
> > From: Eric Bryant <BRYANTE at ghsp.com>
> > Subject: RE: wb lcd display
> >
> > I'd also recommend the addition of some capacitance to the input and
output
> > of the regulator (at least a 0.1 uF on the input and output, and I'd
> > probably also put about an additional 10 uF cap on the output).
> >
> > In addition, place a transorb/zener diode in parallel with the input to
> > clamp the input voltage to ~30 V or so (if you can resist the temptation
to
> > jump-start your car off a 24 V supply, feel free to clamp the input to
20 V
> > or so).  The series diode and the transorb really need to be used for
any
> > in-car application, and this is pretty much bare-minimum for operation
in a
> > vehicle with an internally-suppressed alternator.  It's probably not a
bad
> > idea to put some small amount of series resistance in the input line,
> > either, but this depends greatly on the current demands of the display
unit
> > (something like 5 ohms works pretty well with a small transorb, but the
> > wattage requirements get pretty big if the display unit draws any
> > appreciable amount of power).
> >
> > Eric Bryant
> > mailto:bryante at ghsp.com
> > http://www.bryantperformance.com
> >
> >
> > ------------------------------
> >
> > Date: Mon, 10 Sep 2001 10:26:14 -0600
> > From: "Dave Mumert" <dmumert at telusplanet.net>
> > Subject: Re: wb lcd display
> >
> > Hi
> >
> > I checked over the drawing very briefly.  I have used the LCD driver
before
> > and it works good and is easy to program.  Have you thought of using a
boot
> > loader for the 16F877?  Check at
> > http://www.xs4all.nl/~wf/wouter/pic/wloader/index.html  for a list.  If
> > people were to buy the PIC with the bootloader pre-loaded they would
need no
> > other hardware to program it with their own code.
> >
> > You might consider using one of the National regulators specifically
> > designed for automotive use.  They are protected against reversed
batteries,
> > double battery boosts and 60V load dumps.  I have been using the LM2931,
it
> > is cheap and comes in several packages, the only downside is the
requirement
> > for a 100uF cap on the output.  This regulator along with the
appropriate
> > transorbs should work well.
> >
> > Dave Mumert
> >
> > ------------------------------
> >
> > Date: Mon, 10 Sep 2001 11:30:49 -0700
> > From: "Darrell N." <darrelln at datalog.ab.ca>
> > Subject: Re: wb lcd display
> >
> > Bill Shaw wrote:
> >
> > > While waiting for my DIY-WB I started thinking about a
> > > display for it.
> > > I need help in a few areas:
> > >
> > > 1)  I need someone(s) to review the schematics for technical
> > > correctness before it goes to layout.
> >
> > Can't help you there.  It looks OK to me, but I'm not that familiar with
> > either PICs or the display you are using.
> >
> > > 2)  I need a robust 12V to 5V power supply for it.
> >
> > Use a National LM2931 or similar regulator, it is designed for
automotive
> > applications and can handle load dump, reverse polarity, short circuits,
> > just about everything you can throw at it.  Get rid of your ferrite
beads
> > and put in few hundred uH power inductor in series with the input.  A
> > couple of honkin caps and possibly a MOV or Tranzorb across the input
> > and you should have it handled.
> >
> > > 3)  I need someone to do the PCB layout.
> >
> > That I may be able to handle, if there's demand for the display board on
> > the list.
> >
> > > Yell if you can't print the EPS file and I'll see if I can
> > > get it to you in another format.
> >
> > My Adobe Acrobat converted this file into a PDF.  Let me know if you
> > want me to upload the PDF to incoming.
> >
> > darrell n
> > Calgary, Alberta, Canada
> >
>
> > ------------------------------
> >
> > Date: Mon, 10 Sep 2001 12:20:43 -0600
> > From: "Dave Mumert" <dmumert at telusplanet.net>
> > Subject: Re: wb lcd display, PCB software
> >
> > Hi Darrell
> >
> > Another Calgarian! small world.
> >
> > I have been using a small schematic capture/PCB editor program called
QCAD.
> > It is OK for small projects.
> > Check at http://www.winqcad.com/
> >
> > It is just $99 for 600 pins.  The latest version has copper pour.  The
> > autorouter seems to complete most jobs.
> >
> > Dave Mumert
> > Calgary,AB
> >
> >
> > Date: Mon, 10 Sep 2001 12:43:26 -0600
> > From: Marc Piccioni <piccioni at cadvision.com>
> > Subject: Re: wb lcd display
> >
> > Bill,
> >
> > If you can save the file as a dxf or orcad file I can review it and/or
> > either make any corrections required/send the corrections back to you.
> >
> > Do you have the power budget calculated?
> >
> > /Marc
> >
>
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