Speedos...

[Jonathan]

Want to change the SE over to an electronic speedo (if the price is OK)

Anyone know if the ECU can do this ?

The SE is cable driven but the later cars had a signal wire to an electronic driven speedo from the ECU based on a speed sensor on the driveshaft pole wheel which the SE has but only uses it for silly things like air con (?)

Have yet to get a sillyscope on the wires to see the generated waveform from the sensor and the ECU signals but wondered if anyone has done this before I spend some time on it all ?

Incidently the cable seems a lot more accurate than the electronic setup - might have to make a signal conditioner in there to calibrate the speedo on both cars.

[rydning]

I now we can get electronic VDO that drops right in marked to 300kmh or 200kmh.....

And I think they can be used with abs sensor or the speed output from the ECU.

I did read now from the a VDO paper that it is compatible with:-hall sensor,-magnetic inductiv sensor(speed sensor at the wheel),and oscillator which I think is from the ECU.And its adjusable between 500-400000 pulses/km

Its only to figure how many tooth you have at the wheel and the rollingcircle and then it is easy to calculate. and calibrate.

Edited September 7, 2006 by rydning

[esprits4de]

I know that VDO has offered a conversion kit for old speedos, where the take off where the speedo cable attaches( be it the gearbox or axle) can be replaced with an electric impulse emitter, thus alloowing for an electronic speedo.

[Paul C]

Anyone know what would make the top end of the speedo out?

Initially i thought it was a percentage out across the whole range, but mile per mile

it's pretty much bang on with the sat nav until over 100mph, then the increments of

innaccuaricy begin, at 130 mph on speedo it's 140 mph on GPS, at 140mph on speedo

it's 160mph on the GPS. Have had the real speed (GPS) proved by people following me

so i know that at 160mph my speedo is 20 mph out, however at half that speed (80mph)

the speedo and GPS match within 1mph, so i know it's not gradual. The GPS unit is bang

on in every other car i have used it in, so i know thats fine (backed up by the people

following me test anyhow).

Confuses me. Sorry it's not relevent entirely to your post Jon, but i see the way the

square cable works will be discussed here so i'm kinda interested whats inside the

speedo and how it works, or rather how it does not.

[tinywillyuk]

Jon,

Ran a sillyscopy on the signal coming off the VSS on my S4 - its a tiny tiny pulse (48 tooth wheel iirc, a bit like the ABS wheel). Voltages were small and the decay never complete before the next pulse. Note this was done with wheels turning but car on stands. Tuning the timebase allowed you to see the form quite clearly.

Had a lot of fun running various outputs on screen.

Running Freescan shows the ECU does use it to generate a speed - approx 1 to 2 mph less than the mechanical speedo.

Not sure that helps at all but the data is definitely there and tappable.

[Jonathan]

Paul - most speedos on cars are out at top end - like any analouge gauge they're not all that accurate when out of their specified range (ie 0-70mph).

The only one I have found which is SPOT on is the Elise - at 120 it's within 1-2mph.

My red car is WELL out - at showing 140mph it's doing about 120

Simon - thanks for the info.

Yes it is a 48 pole wheel - I'll have to do my own tests and see if I can convert over either using a tap from the vehicle Speed sensor or the ECU. Will post the results as and when I can get it done !

[fjmuurling]

Hello,

Maybe it is possible to go completely digital, mounting the display on the top forward part of the binnacle so it can be read instead of the view being blocked by the steering wheel. I would be very interested if someone has a solution.

Freek

[sanj]

Want to change the SE over to an electronic speedo (if the price is OK)

Anyone know if the ECU can do this ?

Terminal B8 on ECM connector J2 should be the speed pulse output from the ECM. There may already be a wire going to the dash, Orange with a Brown stripe.

[Jonathan]

Yeah I located the wiring diagram - prob is I don't know if this ECU (from a 1989 car) is comparable to the later ECUs.

If it is I'm laughing

[esprits4de]

Stack has a very nice line of displays that would fit perfectly. Digital analog, but they are always racing oriented. I like the shifting signaling.....

[esprit350]

Anyone know what would make the top end of the speedo out?

Initially i thought it was a percentage out across the whole range, but mile per mile

it's pretty much bang on with the sat nav until over 100mph, then the increments of

innaccuaricy begin, at 130 mph on speedo it's 140 mph on GPS, at 140mph on speedo

it's 160mph on the GPS. Have had the real speed (GPS) proved by people following me

so i know that at 160mph my speedo is 20 mph out, however at half that speed (80mph)

the speedo and GPS match within 1mph, so i know it's not gradual. The GPS unit is bang

on in every other car i have used it in, so i know thats fine (backed up by the people

following me test anyhow).

Confuses me. Sorry it's not relevent entirely to your post Jon, but i see the way the

square cable works will be discussed here so i'm kinda interested whats inside the

speedo and how it works, or rather how it does not.

there was an article in a Lotus club mag a while back, some one asked the same question.

Edited September 9, 2006 by esprit350

[sanj]

Yeah I located the wiring diagram - prob is I don't know if this ECU (from a 1989 car) is comparable to the later ECUs.

If it is I'm laughing

Is it an '89 chargecooled? If so, they are all the same ECU. The '89 non-chargecooled is completely different.

Edited September 9, 2006 by sanj

[Jonathan]

Yeah it's an early SE...looks like good news then !