PistonHeads.com Forum

Speedo

Author
Discussion

Barkychoc

Original Poster:

7,777 posts

127 months

Tuesday 7th September 2010
quotequote all
Norman don't die of shock, I have finally got round to looking at it!

Here's the test setup



Yes Norman that is the same sender you sent me covered in sh!t!
I gave it a bit of a clean.
Don't panic the cog comes off the end by removing a circlip.
The output from the sender is a nice crisp 12v square wave that varies in frequency accoring to the speed (as you'd expect).



Each cm vertically represents 2 volts, so 6 squares = 12 volts.
You can see the volts/div control to the botton right of the pic if you're interested.

Anyway I have spent a lot of time trying to work out the speedo problem to the point that I have just ordered some electronic components, I hope thats OK Norman.

If I'm right then I'll return a fully working speedo to you free of charge.
I have so far identified one problem with the speedo - there may of course be a second fault once that is resolved.

Watch this space!

blues3

248 posts

88 months

Tuesday 7th September 2010
quotequote all
Couple of questions.
If memory serves Norman has a V8, is what you've connected the drill to the gearbox speed sensor? and is it different to the S3 V6?
When you turn the drill off does the speed indication drop slowly or snap to zero.

phillpot

13,271 posts

106 months

Tuesday 7th September 2010
quotequote all
blues3 said:
If memory serves Norman has a V8,
Only in his dreams I think you'll find hehe

Barkychoc

Original Poster:

7,777 posts

127 months

Tuesday 7th September 2010
quotequote all
Both sender and speedo are from a V6 so S2 to S4 are the same as this (2.9 models before the S1.5 owners get upset!)

DJ8226

401 posts

96 months

Tuesday 7th September 2010
quotequote all
Crikey! hope mine doesn't go wrong - last time I saw an ossiloscope was in physics at secondary school some twenty odd years ago!
Advertisement

TonupS2

401 posts

113 months

Tuesday 7th September 2010
quotequote all
DJ8226 said:
Crikey! hope mine doesn't go wrong - last time I saw an ossiloscope was in physics at secondary school some twenty odd years ago!
You are a bit young for this forum! wink

paul.deitch

1,261 posts

180 months

Tuesday 7th September 2010
quotequote all
Is this the new version of the Ebay cheap add on electric turbo?

Gerald-TVR

4,878 posts

120 months

Tuesday 7th September 2010
quotequote all
BLOWN AWAY - GASPS WITH ASTONISHMENT I JUST WISH I UNDERSTOOD, thanks Chris now you can have a new line of work!!!

Norman

Gerald-TVR

4,878 posts

120 months

Tuesday 7th September 2010
quotequote all
phillpot said:
blues3 said:
If memory serves Norman has a V8,
Only in his dreams I think you'll find hehe
hehehehehehehehehehehehehehehehehehehehehehe


blues3

248 posts

88 months

Friday 17th September 2010
quotequote all
Well chaps I have to say this was a great help. You may have been aware of a long running issue that I'd been writing up on the TVRCC web site - http://www.tvr-car-club.co.uk/forum/forum_posts.as... -
The over-revving when drawing to a halt took an interesting turn when I noticed that if I'd stopped on a hill the engine revs died down as normal but in neutral, clutch out, if I rolled forward the engine revs picked up to 2000. The focus now was very firmly on the speed sensor so I took the plunge and pulled it out of the car (bit fiddly!) and set up the test rigs as per above.
This is what we got.....





This is a shot of a single waveform through one cycle, not exactly a crisp squarewave. Turning the sensor sent the whole output into paroxisms. The noise on the positive half cycle is very strange.
Took the car out without the sensor and no problems. Hussar!!


Barkychoc

Original Poster:

7,777 posts

127 months

Friday 17th September 2010
quotequote all
If that sensor is your problem it might be worth trying to open it up - the one I have looked at looks like it is all metal but on closer inspection it looks like 2 seperate parts glued together - there is a glue line if you look carefully.

blues3

248 posts

88 months

Saturday 18th September 2010
quotequote all
I'll give it a go. Do you recall if the sensor you had felt 'notchy' when turned?

Mark_S_24

402 posts

99 months

Saturday 18th September 2010
quotequote all
Barkychoc said:
Norman don't die of shock, I have finally got round to looking at it!

Here's the test setup



Yes Norman that is the same sender you sent me covered in sh!t!
I gave it a bit of a clean.
Don't panic the cog comes off the end by removing a circlip.
The output from the sender is a nice crisp 12v square wave that varies in frequency accoring to the speed (as you'd expect).



Each cm vertically represents 2 volts, so 6 squares = 12 volts.
You can see the volts/div control to the botton right of the pic if you're interested.

Anyway I have spent a lot of time trying to work out the speedo problem to the point that I have just ordered some electronic components, I hope thats OK Norman.

If I'm right then I'll return a fully working speedo to you free of charge.
I have so far identified one problem with the speedo - there may of course be a second fault once that is resolved.

Watch this space!
Thats a fast bench you have there, it looks like it's doing about 143mph hehe

Mark

blues3

248 posts

88 months

Saturday 18th September 2010
quotequote all
Barkychoc said:
If that sensor is your problem it might be worth trying to open it up - the one I have looked at looks like it is all metal but on closer inspection it looks like 2 seperate parts glued together - there is a glue line if you look carefully.
The glue is immovable. Also the whole inside of the unit looks 'potted', as in filled with a sealant.

Ant.

5,227 posts

204 months

Thursday 23rd September 2010
quotequote all
Barky, the diodes for calibration are 1N4148.......

Barkychoc

Original Poster:

7,777 posts

127 months

Thursday 23rd September 2010
quotequote all
blues3 said:
I'll give it a go. Do you recall if the sensor you had felt 'notchy' when turned?
Yes definately notchy - like each notch is being held by a magnet if that makes sense.

blues3

248 posts

88 months

Friday 24th September 2010
quotequote all
Quite right. Got the new replacement yesterday. Turns nice and smooth. Just got to sort out the plug as the old one has to go back on.
The original has Brown, Yellow, Black and the new has Brown, Black/Brown and Yellow/Brown.
Any idea what goes to which?

I think the circuit diagram for the original has :-

Brown - +12v
Black - Earth
Yellow - Signal

Barkychoc

Original Poster:

7,777 posts

127 months

Friday 24th September 2010
quotequote all
I'll have a look in a bit as its still setup on the bench - I can follow the wires from sensor to speedo.

Gerald-TVR

4,878 posts

120 months

Friday 24th September 2010
quotequote all
Dave drop me a PM i can send you a PDF of wiring diagram if that will help

Barkychoc

Original Poster:

7,777 posts

127 months

Friday 24th September 2010
quotequote all
I just had a thought about your raggy waveforms on the scope above - when I tested as above I had a speedo in the circuit - I'm just wondering if your rough waveforms were due to no load?