On Tue, 01 May 2018 00:35:31 +0100, "Dave Plowman (News)"
wrote:

In article ,
Bill wrote:
What I wish I could find again was the online lecture by some American
who had delved into his Jeep's ECU and demonstrated that, for example,
the rev counter was not driven directly from sensors, but via lookup
tables whose inputs combined info from more than one source. If I
remember correctly, he deduced that the rev counter was more of a driver
comfort display rather than direct reality. So you can't trust any of
this stuff.

Can't think of a reason for the rev counter not to be in effect directly
driven.

Directly triggered rev counters from an ignition coil are a remnant of the
1960's and 70's with either a contact breaker or a contactless system but still
using a distributor. Last car produced with contact breaker? 30 years ago?
Last car with a distributor 20 years ago?

The commonly used means of acquiring an engine revs signal requires signal
processing for measuring the passage of the toothed wheel and the position of
the missing tooth on the crank or cam. It then uses this to synchronise the
spark and fuel injection elsewhere in the ECU.

By the mid to late 1980's the crank pulse detector fed the ECU, that then
triggered an (often external) external ignition coil pack and that unit often
fed the moving coil revcounter with a suitable loop current or a PWM signal.

But when everything is in the digital domain it's often easier, cheaper and more
reliable to send everything to the dash over a thin twisted pair to operate a
dozen warning lamps and half a dozen gauges than use a huge bunch of discrete
wires.

Rev counters and indeed most dash gauges including speedos nowadays are either
driven by stepper motor or are a visual widget on an LCD display.

--

"The Other Mike" wrote in message
...
In article ,
Bill wrote:
What I wish I could find again was the online lecture by some American
who had delved into his Jeep's ECU and demonstrated that, for example,
the rev counter was not driven directly from sensors, but via lookup
tables whose inputs combined info from more than one source. If I
remember correctly, he deduced that the rev counter was more of a driver
comfort display rather than direct reality. So you can't trust any of
this stuff.

Can't think of a reason for the rev counter not to be in effect directly
driven.
Rev counters and indeed most dash gauges including speedos nowadays are
either
driven by stepper motor or are a visual widget on an LCD display.

Quite possibly. But, irrespective of how the signal reaches the dashboard
and how it moves the needles on the gauges, I'd still expect the feed for
the gauge to be from a crankshaft rotation sensor that is also used for
determining timing of fuel injection and (for petrol) spark. Likewise I'd
expect the speedo to be driven from a wheel-rotation or final-drive-rotation
sensor. I suppose you could drive the speeo from a GPS receiver and give a
true reading, but you'd still need the wheel rotation as a fall-back in case
of loss of GPS.

Doing it any other way seems unnecessarily complicated.

In article ,
NY wrote:
"The Other Mike" wrote in message
...
In article ,
Bill wrote:
What I wish I could find again was the online lecture by some
American who had delved into his Jeep's ECU and demonstrated that,
for example, the rev counter was not driven directly from sensors,
but via lookup tables whose inputs combined info from more than one
source. If I remember correctly, he deduced that the rev counter was
more of a driver comfort display rather than direct reality. So you
can't trust any of this stuff.

Can't think of a reason for the rev counter not to be in effect
directly driven.
Rev counters and indeed most dash gauges including speedos nowadays
are either driven by stepper motor or are a visual widget on an LCD
display.

Quite possibly. But, irrespective of how the signal reaches the
dashboard and how it moves the needles on the gauges, I'd still expect
the feed for the gauge to be from a crankshaft rotation sensor that is
also used for determining timing of fuel injection and (for petrol)
spark. Likewise I'd expect the speedo to be driven from a
wheel-rotation or final-drive-rotation sensor. I suppose you could
drive the speeo from a GPS receiver and give a true reading, but you'd
still need the wheel rotation as a fall-back in case of loss of GPS.

Doing it any other way seems unnecessarily complicated.

Point I was making was that I can't see any reason why you'd want a tach
to read anything other than true engine RPM. No point in fitting one
unless it's reasonably accurate. After all a rev counter is of zero use to
many drivers. For those who can make use of it, needs to be reasonably
accurate.

--
*It's o.k. to laugh during sexŒ.Œ.just don't point!

Dave Plowman London SW
To e-mail, change noise into sound.

On 04/05/18 09:56, NY wrote:
"The Other Mike" wrote in message
...
In article ,
Â* Bill wrote:
What I wish I could find again was the online lecture by some American
who had delved into his Jeep's ECU and demonstrated that, for example,
the rev counter was not driven directly from sensors, but via lookup
tables whose inputs combined info from more than one source. If I
remember correctly, he deduced that the rev counter was more of a
driver
comfort display rather than direct reality. So you can't trust any of
this stuff.

Can't think of a reason for the rev counter not to be in effect directly
driven.
Rev counters and indeed most dash gauges including speedos nowadays
are either
driven by stepper motor or are a visual widget on an LCD display.

No, They are normally analogue millammeters.
Driven by the cars computer systems.

Quite possibly. But, irrespective of how the signal reaches the
dashboard and how it moves the needles on the gauges, I'd still expect
the feed for the gauge to be from a crankshaft rotation sensor that is
also used for determining timing of fuel injection and (for petrol)
spark. Likewise I'd expect the speedo to be driven from a wheel-rotation
or final-drive-rotation sensor. I suppose you could drive the speeo from
a GPS receiver and give a true reading, but you'd still need the wheel
rotation as a fall-back in case of loss of GPS.

Doing it any other way seems unnecessarily complicated.


--
Canada is all right really, though not for the whole weekend.

"Saki"

The Natural Philosopher wrote:

The Other Mike wrote:

Rev counters and indeed most dash gauges including speedos
nowadays are either driven by stepper motor or are a visual widget
on an LCD display.

No, They are normally analogue millammeters.
Driven by the cars computer systems.

Mine (7 years old) certainly is a stepper-motor, the speedo and rev
needles do a precise 'sweep' as part of the lamp check sequence when
turning the ignition on.

On Fri, 04 May 2018 10:59:28 +0100, Andy Burns wrote:

The Natural Philosopher wrote:

The Other Mike wrote:

Rev counters and indeed most dash gauges including speedos nowadays
are either driven by stepper motor or are a visual widget on an LCD
display.

No, They are normally analogue millammeters.
Driven by the cars computer systems.

Mine (7 years old) certainly is a stepper-motor, the speedo and rev
needles do a precise 'sweep' as part of the lamp check sequence when
turning the ignition on.

And mine is a visual widget on an LCD screen.

--
My posts are my copyright and if @diy_forums or Home Owners' Hub
wish to copy them they can pay me £1 a message.
Use the BIG mirror service in the UK: http://www.mirrorservice.org
*lightning surge protection* - a w_tom conductor

In article ,
Bob Eager wrote:
Mine (7 years old) certainly is a stepper-motor, the speedo and rev
needles do a precise 'sweep' as part of the lamp check sequence when
turning the ignition on.

And mine is a visual widget on an LCD screen.

Mine has both an analogue speedo and a digital display. And a clock
display at all times. Or rather two, as there is a second one on the ICE
display.

--
*One tequila, two tequila, three tequila, floor.

Dave Plowman London SW
To e-mail, change noise into sound.

Tim Streater wrote:

Andy Burns wrote:

the speedo and rev needles do a precise 'sweep' as part of the lamp
check sequence when turning the ignition on.

When looking for a new car 18 months ago, I rejected one model
precisely because it does that.

What's wrong with it? can be turned off by OBD-II

In article ,
Tim Streater wrote:
But it wasn't just that. It was also that all the heater controls were
on the touch display. So you're driving along concentrating on the
road, and can't adjust the heating without taking your gaze *off* the
road.

Time was was cars had sliders etc for climate control. One could
operate all those without looking at them.

If it is a decent climate control system, no need to adjust it? Apart from
to say defrost on first start on a cold day?

And sliders ain't the best way to set the temperature on climate control.
Toggling a display to the required temperature is best. Which is probably
why I've only seen slide controls on older basic heaters.

--
*Microsoft broke Volkswagen's record: They only made 21.4 million bugs.

Dave Plowman London SW
To e-mail, change noise into sound.

Tim Streater wrote:
In article , Andy Burns
wrote:

Tim Streater wrote:

Andy Burns wrote:

the speedo and rev needles do a precise 'sweep' as part of the lamp
check sequence when turning the ignition on.

When looking for a new car 18 months ago, I rejected one model
precisely because it does that.

What's wrong with it? can be turned off by OBD-II

Because it's ****in' irritating and smacks of oh look what we can do
aren't we clever.

But its harmless.

But it wasn't just that. It was also that all the heater controls were
on the touch display. So you're driving along concentrating on the
road, and can't adjust the heating without taking your gaze *off* the
road.

Now there I agree with you. Touch screens for basic heat & ventilation
controls are a truly terrible and dangerous idea.

Hopefully theyll be banned when people come to realise that theyre more
dangerous than mobile phones.

Tim


--
Please don't feed the trolls

On 04/05/2018 11:14, Tim Streater wrote:
In article , Andy Burns
wrote:

The Natural Philosopher wrote:

The Other Mike wrote:

Rev counters and indeed most dash gauges including speedos
nowadays are either driven by stepper motor or are a visual widget
on an LCD display.

No, They are normally analogue millammeters.
Driven by the cars computer systems.

Mine (7 years old) certainly is a stepper-motor, the speedo and rev
needles do a precise 'sweep' as part of the lamp check sequence when
turning the ignition on.

When looking for a new car 18 months ago, I rejected one model
precisely because it does that.



You do understand that it is just establishing its start position..
it drives the stepper for long enough to hit the end stop and then backs
off by the number of steps to get to the start point.
Lots of stuff does the same, for example the moving vents on air
conditioners.

Huge wrote:

And some modern cars don't have any physical dials at all.

Of course, mine has the option to display a reasonably large digital
speedo on the dash, which I tend to find easiest to read, especially
since '30' does get a figure on the analogue dial.

Since someone has mentioned 'fudging' e.g. the rpm dial, I feel the
digital speedo must do quite a lot of smoothing, as it never 'flickers'
between a number and +/- 1mph

On 04/05/18 11:25, Andy Burns wrote:
Huge wrote:

And some modern cars don't have any physical dials at all.

Of course, mine has the option to display a reasonably large digital
speedo on the dash, which I tend to find easiest to read, especially
since '30' does get a figure on the analogue dial.

Since someone has mentioned 'fudging' e.g. the rpm dial, I feel the
digital speedo must do quite a lot of smoothing, as it never 'flickers'
between a number and +/- 1mph

just add a bit of hysteresis

So to get to 30mph uyou have to do 30.5mph, but to get down to 29mph you
have to do 29.5....


--
Theres a mighty big difference between good, sound reasons and reasons
that sound good.

Burton Hillis (William Vaughn, American columnist)

Huge wrote:

Andy Burns wrote:

especially since '30' does get a figure on the analogue dial.

(I assume there's a "not" missing there?)

There was

We prefer the digital speedo on my wife's car, also, but you can't have
both a digital speedo and a clock, which annoys us.

check if it has a 'driving school' mode buried in the menus, that allows
me to display a 3rd speedo on the radio display, but I prefer the
station information.

My car has analogue and
digital clock and speedo both. But no oil pressure or temperature dial
(or dipstick. Grrrrr.)

I get a temperature dial, which I don't think is a stepper (nor is the
fuel gauge) digital dipstick here too, and I presume a red icon buried
somewhere on the dash.

On 04/05/18 11:19, Huge wrote:
On 2018-05-04, Andy Burns wrote:
The Natural Philosopher wrote:

The Other Mike wrote:

Rev counters and indeed most dash gauges including speedos
nowadays are either driven by stepper motor or are a visual widget
on an LCD display.

No, They are normally analogue millammeters.
Driven by the cars computer systems.

Add another topic to the oh-so-long list of those that Turnip either knows
nohing about or generalises from his limited and elderly experience.

Oh dear. So why do you not actually cite every model of car that uses
mechanical speedos, electronic analog and electronic stepper?

Mine (7 years old) certainly is a stepper-motor, the speedo and rev
needles do a precise 'sweep' as part of the lamp check sequence when
turning the ignition on.

And some modern cars don't have any physical dials at all.


I know that. I am not concerned with e.g. LCD panels - just the
prevalence of stepper versus analogue meters


--
There is something fascinating about science. One gets such wholesale
returns of conjecture out of such a trifling investment of fact.

Mark Twain

In article ,
Huge wrote:
No, They are normally analogue millammeters.
Driven by the cars computer systems.

Add another topic to the oh-so-long list of those that Turnip either knows
nohing about or generalises from his limited and elderly experience.

Not so sure. A stepper motor - unless extremely sophisticated - would be
seen to 'step' Like chronometric types. Neither speedos or rev counters on
cars are generally very accurate, so well within the capabilities of a
conventional meter. It would also be trivial to make those sweep up to
maximum at switch on as a self check if needed.

Not saying some ain't stepper motors - or look like one - which would also
be easy to frig.

--
*The average person falls asleep in seven minutes *

Dave Plowman London SW
To e-mail, change noise into sound.

On 04/05/2018 13:57, Dave Plowman (News) wrote:
In article ,
Huge wrote:
No, They are normally analogue millammeters.
Driven by the cars computer systems.

Add another topic to the oh-so-long list of those that Turnip either knows
nohing about or generalises from his limited and elderly experience.

Not so sure. A stepper motor - unless extremely sophisticated - would be
seen to 'step' Like chronometric types. Neither speedos or rev counters on
cars are generally very accurate, so well within the capabilities of a
conventional meter. It would also be trivial to make those sweep up to
maximum at switch on as a self check if needed.

Not saying some ain't stepper motors - or look like one - which would also
be easy to frig.


The problem with analogue meters is that they cost more.
They cost more because they need to be made robust and damped so they
don't bounce about when the car does.

In article ,
The Other Mike wrote:
Can't think of a reason for the rev counter not to be in effect directly
driven.

Directly triggered rev counters from an ignition coil are a remnant of
the 1960's and 70's with either a contact breaker or a contactless
system but still using a distributor. Last car produced with contact
breaker? 30 years ago? Last car with a distributor 20 years ago?

Of course. What I meant is I can't see any reason to 'frig' its reading,
unlike with other gauges, as I explained.

--
*You're never too old to learn something stupid.
Dave Plowman London SW
To e-mail, change noise into sound.