arrgggghhhhh!!!! <insert expletive>
02GF74 - 21/2/07 at 08:59 PM
Those of you who have been paying attention will know I have been working on using a PIC to control a motor to turn a speedometer - was a cheap,
moneywise at least, alternative to spending £ 200 on a speedo. After overcoming many hurdles it was working.
Well tonight the speedo has jammed solid, bloody czech rubbish :mad - I guess should have seen the warning signs when the hundreds digit did not turn
on the odometer. Oh well, SVA retest in 4 days time....... 
.... but I have a bike speedo with LED lighting fitted so that should work, I hope; just need to plug in the hole in the dash 
So what do I do? Fork out £ 200 on an electronic speedo? Make my own digital speedo? (don't like digital displays) Rip out the guts and use a
stepper motor to turn a pointer - could do it as have the motor but can't face it at this moment in time.
So much time spent .......
David Jenkins - 21/2/07 at 09:12 PM
Was the speedo one of the fail points? If you fit the bike speedo, can you be sure that it is calibrated correctly?
If you're unsure of getting it fixed by the SVA - postpone it now, and avoid any penalties. They won't mind at all.
David
02GF74 - 21/2/07 at 09:19 PM
yep - speedo was reading about 1/2 actual speed.
I think I can handle the bike speedo programming since I have measured the diameter and know the value of pi the number will be bigger than
rolling value but aren't speedo's required to over-read? and I'm pretty sure it will be within the limits specified in the manual.
In any case, I can alway reprogram it on the day ; as for postponing, my 6 months period for retest is almost up. 
David Jenkins - 21/2/07 at 09:34 PM
quote:
Originally posted by 02GF74
In any case, I can alway reprogram it on the day ; as for postponing, my 6 months period for retest is almost up.
Ahh - I see your problem...
Just make sure that you have the reprogramming instructions handy at the retest.
<begin egg-sucking info>
Oh - and don't use the actual radius of the tyre in your calculations, use the rolling radius (allowing for tyre squash at the bottom), or
measure the circumference with a tape. Better still, make a chalk mark at the bottom of the wheel and on the ground, roll the car forward until
you've rolled the wheel say 10 times, and mark the floor again & measure the distance between the marks.
<end egg-sucking info>
But you probably knew that already!
Good luck at the retest, whatever you end up doing!
David
[Edited on 21/2/07 by David Jenkins]
omega0684 - 21/2/07 at 10:45 PM
hi there,
i think that paying £200 for a speedo is a little extreme, you can get really nice brand new smiths speedo's for around £100 (if you want smiths
of course) i got mine off ebay for £89, brand new and boxed with instructions and i got the rev counter for £26.
hope this helps
Alex
P.S good luck with sva retest
jon_boy - 22/2/07 at 10:38 AM
I have a vdo jobbie (with no sender at the mo) and if you get desperate you cvan borrow it until after sva if you like. Jon
02GF74 - 22/2/07 at 09:11 PM
thanks for offer but the plan B has been put into place (bike speedo, all wired up etc
and hole in dash for original speedo blanked off.
just need to find some 1.8 degree stepper motors so can start to make my own speedo.
re: £ 200 for speedo - this includes the sensor too.
burton power, on new catalogue, mention a sensor that fits into the gearbox whcih is something that, if cheap, would be very handy (I'm in the
process of making one , on the mk2 version already ....).
stevebubs - 25/2/07 at 01:40 AM
quote:
Originally posted by 02GF74
yep - speedo was reading about 1/2 actual speed.
If this is the case, can you not just double the number of magnets?
(or am I missing something? - it is 1.30am after all)