by dapinky » Sat 15.08.2020, 12:40
If you follow Rons link it'll take you to my thread..... but I never finalised the posts on it!
Basically, taking the pulse count from the back of the speedo didn't work - and it isn't how the Vauxhall unit ever took it's pulse on a Vectra/Astra/Omega (as I later found out).
I'm no electronics engineer (and my friendly local one with an Elan and an Oscilloscope was sunning it up in Spain at the time and not able to do the measurements needed), so I don't know if it was a case of wrong frequency, insufficient ampltude or wrong wave pattern that was the problem.....
.....anyway, I had no idea if it needed a sine/square conversion, an amplification, or a multiplication/division of frequency.....
..... so I looked at how the Vauxhalls did it.
They take the signal from the ABS unit, so we were a bit buggered.
Except for the Astra G, which has CC as an option, but takes the pulse from a single reluctor ring and pickup. I don't know if the Astra takes it from the front, rear left or right wheel, and it doesn't really matter. I simply found a Vauxhall reluctor ring with the correct diameter to be an (almost) interference fit on the CV joint on the OS Elan driveshaft. The signal is picked up by a 'standard' Vauxhall ABS sensor which I had to mount on the hub with a bit of a bracket.
The signal connects to a Vauxhall relay/switch/circuit thingy (brown coloured box which looks like a standard relay, but has an electronic circuit inside) and feeds the Cruise Control box.
It all now works as it should, but it isn't as simple or straightforward as i first thought it should be - mainly because of the need to aquire the speed signal.