[xj] Trip computer: unmasked!

OK, it took a few pieces of test equipment I didn’t have,
which took buying them on ebay and then repairing them
(because all the good deals on ebay are for broken
things…), plus buying a few trip computers on ebay, but I
finally have all the details gathered together on one web page:

http://www.backglass.org/duncan/jag/ifu/

Corrections/comments welcome. (Comments about how I spend
my time, or about my being obsessive about trivial stuff
like this not necessary!)

I have a couple of units with dead or half-dead displays.
If I ever find a cure for those (other than the unobtainable
display glass itself being bad) I’ll add that to the page.–
Duncan Brown 1985 SIII XJ6
Grayslake, IL, United States
–Posted using Jag-lovers JagFORUM [forums.jag-lovers.org]–
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In reply to a message from frobozz sent Sun 24 Apr 2005:

Very nice, Duncan! Thank you for sharing it.–
The original message included these comments:

Corrections/comments welcome. (Comments about how I spend
my time, or about my being obsessive about trivial stuff
like this not necessary!)


al mclean '93 XJS 4.0 79 SII XJ6 85 4.2 Daimler Sovereign
Telford, United Kingdom
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Very high speed Duncan, This is a great addition to the archives. It is
truly commendable.

Bob Donnelly
84 SIII
94 XJ40
Suffolk, VA

OK, it took a few pieces of test equipment I didn’t have,
which took buying them on ebay and then repairing them
(because all the good deals on ebay are for broken
things…), plus buying a few trip computers on ebay, but I
finally have all the details gathered together on one web page:

http://www.backglass.org/duncan/jag/ifu/

Duncan Brown 1985 SIII XJ6
Grayslake, IL, United StatesSubject: [xj] Trip computer: unmasked!

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Excellent Duncan! No, you’re not wasting your life. :]–
Alex
79xj6L SII (BRG + wires)
86xj6 SIII (Black)
61 Sprite MkII (Red)
Menlo Park, Calif.

frobozz wrote:

OK, it took a few pieces of test equipment I didn’t have,
which took buying them on ebay and then repairing them
(because all the good deals on ebay are for broken
things…), plus buying a few trip computers on ebay, but I
finally have all the details gathered together on one web page:

http://www.backglass.org/duncan/jag/ifu/

Corrections/comments welcome. (Comments about how I spend
my time, or about my being obsessive about trivial stuff
like this not necessary!)

I have a couple of units with dead or half-dead displays.
If I ever find a cure for those (other than the unobtainable
display glass itself being bad) I’ll add that to the page.

===================================================
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Duncan,
echoing other’s comments, an excellent job! From your postings, you seem to
know pretty much how it works, so to my question… Do you think this unit is
reworkable to use an LCD display instead of the dim LED display? I’ve looked
at mine, but I have very limited background in electronic circuits, so I was
never sure it would be possible. I think a nice LCD display, either attached
or separated from the unit, would be a nice addition to usability of he
unit…

Ken

87 SIII - “Fireball”
180,000+ Miles - A Great Daily Driver

87 SIII VDP
110,000+ Miles, my (soon to be) New Daily Driver===================================================
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In reply to a message from Ken Davis sent Tue 26 Apr 2005:

Do you think this unit is reworkable to use an LCD
display instead of the dim LED display?

What’s in there now is a vacuum-flourescent display (VFD)
which is actually one of the brighter display technologies
out there, even today. LCDs are not visible in the dark,
unless they are backlit, and adding a backlit display is
going to be problematic in the same footprint, even ignoring
the completely different ways that the two display types are
driven.

Three ideas come to mind:

– altering the circuit so that the display does not dim
when the headlights are on. I drive with the lights on in
the day, making the display nearly impossible to read. I
can’t imagine it would be too bright at night if it wasn’t
dimmed; nothing on a Birtish car dash has ever been
described as ‘‘too bright’’!

– altering the circuit to pump up the brightness of the
display. This risks long term display damage though, and
I’m not sure (yet) how their drive circuit compares with the
safe specs for the display.

– changing out the green filter plastic in front of the
display. What’s in there is quite dark, and has perhaps
even darkened with age. Something lighter might allow the
display to be read more easily, without being so light that
you can see all the ugliness of the display part itself
(which was the reason for the filter.) If you really want
display brightness at all costs, you could just take out the
filter or substitute a piece of clear plastic. It’s just
staked into the opening by melting some of the surrounding
frame over it, from the back.–
Duncan Brown 1985 SIII XJ6
Grayslake, IL, United States
–Posted using Jag-lovers JagFORUM [forums.jag-lovers.org]–
–Support Jag-lovers - Donate at http://www.jag-lovers.org/donate04.php

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Thanks Duncan,
Didn’t even think of a VFD… Hell, didn’t know it even existed. I’m going
to scrounge around and find an old one and play a little with it. Nothing
like you’ve done, but I’ll use your experience thus far as a reference point
to learn all about it… Actually, that’ll be 2nd… 1st is getting Cruise
control working on the new one… Looking at the obvious things now, like
bad fuses and switches, loose vacuum etc before I get into the in-cabin
control module…

Ken
87 SIII - “Fireball”
180,000+ Miles - A Great Daily Driver

87 SIII VDP
110,000+ Miles, my (soon to be) New Daily Driver> What’s in there now is a vacuum-flourescent display (VFD)

which is actually one of the brighter display technologies
out there, even today. >

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As Duncan points out, the display is in fact one type to choose for bright
conditions. LCDs are chosen by manufacturers for one main reason now –
because they’re cheap, not because they’re good! A distant acquaintance here
has the patent on LCDs. Yes, he’s very rich. Too bad we’re not relatives.
:]–
Alex
79xj6L SII (BRG + wires)
86xj6 SIII (Black)
61 Sprite MkII (Red)
Menlo Park, Calif.

Ken Davis wrote:

Duncan,
echoing other’s comments, an excellent job! From your postings, you seem to
know pretty much how it works, so to my question… Do you think this unit is
reworkable to use an LCD display instead of the dim LED display? I’ve looked
at mine, but I have very limited background in electronic circuits, so I was
never sure it would be possible. I think a nice LCD display, either attached
or separated from the unit, would be a nice addition to usability of he
unit…

===================================================
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In reply to a message from frobozz sent Tue 26 Apr 2005:

I’ve updated the page with a mod for leaving the display
bright all the time, even with the headlights on. This will
help make the display visible in the daytime. I tried it on
mine and it works great! I haven’t driven it at night yet
though, so I don’t know for sure that the bright display
won’t be annoying. I can’t imagine it will… but I’ll
report back after dark.

http://www.backglass.org/duncan/jag/ifu/--
Duncan Brown 1985 SIII XJ6
Grayslake, IL, United States
–Posted using Jag-lovers JagFORUM [forums.jag-lovers.org]–
–Support Jag-lovers - Donate at http://www.jag-lovers.org/donate04.php

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Wow, Duncan!!!..that is one fine write-up and pics. I wish I knew more
about things electrical, but enjoyed reading/looking just the same. So,
exactly what is to be done to make the LED’s brighter on an 87 xj6? Just
clipping the R23 resistor??? Thanks for such a useful resource. This
should go to the FAQ’s!

Thanks,

Mike Vaughn
Oviedo, FL
87 xj6 SIII

In reply to a message from frobozz sent Tue 26 Apr 2005:

I’ve updated the page with a mod for leaving the display
bright all the time, even with the headlights on. This will
help make the display visible in the daytime. I tried it on
mine and it works great! I haven’t driven it at night yet
though, so I don’t know for sure that the bright display
won’t be annoying. I can’t imagine it will… but I’ll
report back after dark.

http://www.backglass.org/duncan/jag/ifu/===================================================
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In reply to a message from Mike Vaughn sent Mon 2 May 2005:

In all of my trolling of ebay for cheap/broken trip
computers to study, I never came up with one of the 1987-era
ones. I assume it didn’t change much, so it’s likely still
R23 in that position, but without seeing one I can’t say for
sure. Basically it’s the resistor that the red wire
connects to, that’s the one you want to cut.

(If someone has a broken/unloved trip computer with part
number DAC4296 (US) or DAC4295 (R-O-W) they’d give or sell
me cheap, let me know…)–
The original message included these comments:

Wow, Duncan!!!..that is one fine write-up and pics. I wish I knew more
about things electrical, but enjoyed reading/looking just the same. So,
exactly what is to be done to make the LED’s brighter on an 87 xj6? Just
clipping the R23 resistor??? Thanks for such a useful resource. This
should go to the FAQ’s!


Duncan Brown 1985 SIII XJ6
Grayslake, IL, United States
–Posted using Jag-lovers JagFORUM [forums.jag-lovers.org]–
–Support Jag-lovers - Donate at http://www.jag-lovers.org/donate04.php

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Mike Vaughn wrote:

Wow, Duncan!!!..that is one fine write-up and pics. I wish I knew more
about things electrical, but enjoyed reading/looking just the same. So,
exactly what is to be done to make the LED’s brighter on an 87 xj6? Just
clipping the R23 resistor???

Actually it is a less permanent way, Mike…

As the lights are turned on power is applied to the computer via the
red/blue wire to it. This dims the light, so disconnecting this wire;
no power - no dimming…

Frank
xj6 85 Sov Europe (UK/NZ)===================================================
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In reply to a message from Frank Andersen sent Mon 2 May 2005:

Er yes, but then you also get no illumination of the little
legend strip above the buttons! If that’s OK for someone
then yes, popping the lights-on wire out of the connector
would be a simpler solution.–
The original message included these comments:

Actually it is a less permanent way, Mike…
As the lights are turned on power is applied to the computer via the
red/blue wire to it. This dims the light, so disconnecting this wire;
no power - no dimming…


Duncan Brown 1985 SIII XJ6
Grayslake, IL, United States
–Posted using Jag-lovers JagFORUM [forums.jag-lovers.org]–
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frobozz wrote:

In reply to a message from Frank Andersen sent Mon 2 May 2005:

Er yes, but then you also get no illumination of the little
legend strip above the buttons! If that’s OK for someone
then yes, popping the lights-on wire out of the connector
would be a simpler solution.

Your dead right, of course, Duncan…!

I was a bit half-hearted here as the d… strip is dark and I haven’t
sourced a replacemant bulb yet. And I have no difficulties reading the
display at night anyway - but a solution to make the display show up in
sunlight would be welcome…:slight_smile:

Frank
xj6 85 Sov Europe (UK/NZ)===================================================
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It’s always the red wire – remember all the Bond and other spy movies?!–
Alex
79xj6L SII (BRG + wires)
86xj6 SIII (Black)
61 Sprite MkII (Red)
Menlo Park, Calif.

frobozz wrote:

In reply to a message from Mike Vaughn sent Mon 2 May 2005:

In all of my trolling of ebay for cheap/broken trip
computers to study, I never came up with one of the 1987-era
ones. I assume it didn’t change much, so it’s likely still
R23 in that position, but without seeing one I can’t say for
sure. Basically it’s the resistor that the red wire
connects to, that’s the one you want to cut.

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Duncan, you could add a photodiode and transistor to automatically control
brightness based on ambient light – just a small drill hole in the panel for
the light pickup (since we’re having our way with TC mods now :).–
Alex
79xj6L SII (BRG + wires)
86xj6 SIII (Black)
61 Sprite MkII (Red)
Menlo Park, Calif.

frobozz wrote:

In reply to a message from frobozz sent Tue 26 Apr 2005:

I’ve updated the page with a mod for leaving the display
bright all the time, even with the headlights on. This will
help make the display visible in the daytime. I tried it on
mine and it works great! I haven’t driven it at night yet
though, so I don’t know for sure that the bright display
won’t be annoying. I can’t imagine it will… but I’ll
report back after dark.

http://www.backglass.org/duncan/jag/ifu/

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In reply to a message from Cannara sent Mon 2 May 2005:

Duncan, you could add a photodiode and transistor to
automatically control brightness based on ambient
light – just a small drill hole in the panel for
the light pickup (since we’re having our way with
TC mods now :).

Don’t think that hadn’t occurred to me! But A) I hate to
spend that much effort on what is largely a useless
accessory (it’s a good clock, plus a toy to play with), and
B) I hate to spend that much effort making anything on a
British dash dimmer! It would be like adding a photocell to
the main dash illumination circuit, to make sure the
instruments never got too bright at night, heh heh heh…

I tried it last night with the full brightness at night and
it sure doesn’t look too bright to me. Anyone else who
tries this mod and finds it too bright, let us know… I
don’t think we’ll hear from anyone.–
Duncan Brown 1985 SIII XJ6
Grayslake, IL, United States
–Posted using Jag-lovers JagFORUM [forums.jag-lovers.org]–
–Support Jag-lovers - Donate at http://www.jag-lovers.org/donate04.php

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Good points Duncan! I almost made the dimmer useful by getting brighter bulbs
for our at Radio Shack – 200mA ratings. But, even that only makes a teeny
part of the dimmer’s sweep useful. You may like this, however…

The piece de resistance for this mod is the addition of two small green
LEDs in the upper wings of the plastic escutcheon so one can actually tell a
turn signal has been set on!

http://www.jag-lovers.org/v.htm?1074061153

It’s actually a relief to drive now without having to worry that the parking
brake was left on for how many miles? :]–
Alex
79xj6L SII (BRG + wires)
86xj6 SIII (Black)
61 Sprite MkII (Red)
Menlo Park, Calif.

frobozz wrote:

In reply to a message from Cannara sent Mon 2 May 2005:

Duncan, you could add a photodiode and transistor to
automatically control brightness based on ambient
light – just a small drill hole in the panel for
the light pickup (since we’re having our way with
TC mods now :).

Don’t think that hadn’t occurred to me! But A) I hate to
spend that much effort on what is largely a useless
accessory (it’s a good clock, plus a toy to play with), and
B) I hate to spend that much effort making anything on a
British dash dimmer! It would be like adding a photocell to
the main dash illumination circuit, to make sure the
instruments never got too bright at night, heh heh heh…

I tried it last night with the full brightness at night and
it sure doesn’t look too bright to me. Anyone else who
tries this mod and finds it too bright, let us know… I
don’t think we’ll hear from anyone.

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In reply to a message from Cannara sent Mon 2 May 2005:

The SIII turn signal indicators are a little more visible, I
think. The blinky handbrake indicator is very clever, but I
was thinking of adding a beeper/buzzer for that and the
headlights. Ignition off + headlights on = beeper, that’s
simple enough, but handbrake on + ??? = beeper, that’s
harder. Gearshift-not-in-Park? Or heck, maybe handbrake on

  • ignition on = beeper, since it would be so rare for that
    combo to exist on purpose. As long as the beeper were
    gentle, not annoying. (I already desoldered a lead from the
    annoying piezo buzzer in the seatbelt unit!)–
    The original message included these comments:

The piece de resistance for this mod is the addition of two small green
LEDs in the upper wings of the plastic escutcheon so one can actually tell a
turn signal has been set on!
http://www.jag-lovers.org/v.htm?1074061153
It’s actually a relief to drive now without having to worry that the parking
brake was left on for how many miles? :]


Duncan Brown 1985 SIII XJ6
Grayslake, IL, United States
–Posted using Jag-lovers JagFORUM [forums.jag-lovers.org]–
–Support Jag-lovers - Donate at http://www.jag-lovers.org/donate04.php

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I know it has been a while since you wrote the excellent piece on the trip computer, but I’m interested to know if you are still working on the issue. I have collected a number of these things and I believe all of them to be functional, but before I say that I’d like to bench test them. Most of the information to enable that is in your piece, but the one bit that is not is the amplitude of the speed pulse. I’m assuming this the pulse is a square wave that cycles from 0 to +v, (off to some voltage) at the frequency you describe, but do you know what the +v level is?
Also any headway on the display or the interface unit?
Thanks, Niles