Path: utzoo!utgpu!news-server.csri.toronto.edu!rpi!usc!cs.utexas.edu!uunet!ogicse!milton!sumax!ole!ssave
From: ssave@ole.UUCP (Shailendra Save)
Newsgroups: sci.electronics
Subject: Re: Digital dash (was: Inductive pickups.
Summary: Intelligent Dash.
Message-ID: <1973@ole.UUCP>
Date: 3 Jun 91 04:18:03 GMT
References: <1970@ole.UUCP> <1991May30.151040.50@cmkrnl.uucp>
Organization: Seattle Silicon Corp., Bellevue, WA.
Lines: 91

In article <1991May30.151040.50@cmkrnl.uucp>, Mr. Haha Jamie writes:
> 
> Projects for such have been appearing in the hobby mags every now and then for
> almost forever.  There was even one in one of the trade magazines, _EDN_ I
> believe, circa 1974 (!) or 75 or so. That one was for a motorcycle. 

  I am aware of this. The idea behind this venture is to make more
  than a just the run of the mill "digital dash"  Most articles
  (projects) in the mags do not come close. Even if they did, I would
  not use them. Takes the fun out of experimenting.

> Personally I would steer clear (ha ha) of a digital dash.  Saab, who builds
> fighter planes as well as cars, has done extensive research on what kinds of
> gauges can be read the most easily.  The answer?  Old-fashioned analog, with a

   This is perfectly true. But in the case of the speedometer, I would
   certainly like to have a completely digital readout. It is just
   easier to read.  The tach remains "analog" though I am still
   using comparators to make comparisons to light LEDs. The advantage:
   I can use different colored leds. I have a green section, an
   orange, and a red. When I am in the orange, I know I am approaching
   red. 

   As far as reading battery voltage, I do need to know when I am
   charging and when I am discharging. (think of multicolored digital
   7-seg displays).

> moving pointer against a stationary background.  The pointer and scale can be
> electronically generated (ie on a computer-generated display) or mechanical,
> circular or bar-graph style, but whatever the variant, it beats a digital
> display six ways from zero.  You see, it is usually far more important to know
> that "you're nearly at redline" than that "engine speed is 6,253.8 RPM", and
> it's MUCH more important to know that "your oil pressure is low" than that
> "your oil pressure is 21.3 psi". 
> 
  BTW, the resolution of the tach is 50 rpm. (borderline too much) and
  oil will be green-orange-red.

> For rapidly-changing things like a tach, the pointer and scale have another
> big advantage:  It is easy to see how fast the reading is changing.  This is
> almost impossible to derive from a digital readout.  
> 
> Color-coding the scale for good, warning, and bad ranges -- or adding
> color-coded idiot lights -- obviously helps to draw attention to those gauges
> that need reading at the moment.  But color-coding gets tricky even for

  Not so idiotic.  The way I designed all of the stuff, is that as
  long as all the lights are green, I am fine. At a glance, I can find
  out if anything is wrong without actually taking the complete
  reading. For example, if I look down, and see everything green, I
  know everything is normal. If I look down, and see rpm approaching
  red (ie orange) I do a double take and see how close I am to it in
  terms of actual rpms..

> something as simple as an automobile engine.  For instance, my water temp.
> gauge swings almost up to the red part of the scale as the car warms up, and
> then the thermostat opens and it goes down to the middle of its range where
> it's supposed to be.  What would be nifty would be something that would draw my
> attention to that gauge if the reading stayed up near the redline for more than
> a few minutes.  

  I think you need to have your thermostat looked at. The temp should
  approach red. Never be *in* it. Especially with summer coming up.
> 
> How about a heads-up display?  And ONLY display those instruments that are
> indicating out of "nominal" range.  Mount a backlit LCD atop your dash, wire it
> so the display is mirror-imaged, and read its reflection off the windshield. Of
> course since both the inner and outer surfaces of the windshield will reflect
> you will get some ghosting in the vertical dimension.  This is, I think, why
> the fighters with heads-up displays have a special piece of optic surface just
> for this purpose (with an antireflection coating on the far surface). 

  Thought of this one. Learjets have this. The only problem with this
  is that at noon or high sun, the reflection is almost non-existent.
  Would require high powered laser leds to light this.

  One final note. Digital becomes better when there is something
  intellegent you can do with the reading. I intend to use a 6811
  microcontroller which will tell me things like trip distance, miles
  per gallon, total distance, shift up (rpm too high), shift down
  (angle of car upwards or downwards, rpm too low)  and other things
  like that. Why all this? Because it is fun. Because it comes free.
  I have lots of free ports on the I/O. Because it is a challenge.
  Cars are some of the noisiest environments you can work with.
  Because I like to do things myself. And finally, because I don't 
  have a tach or battery guage on my dash ^_^
> 
> 	--- Jamie (Haha)Hanrahan, Kernel Mode Consulting, San Diego CA

  Shailendra
  ssave@caen.engin.umich.edu