[DeTomaso] More cruise control issues

[Thomas Tornblom]

Charles McCall skrev:
> On Mon, Aug 31, 2009 at 7:26 PM, <asajay at asajay.com> wrote:
> 
>> -That- brought back memories.
>>
>> I used an old CompuCruise computer in an older car of mine that had a
>> manual transmission.  The Tach signal was only -one- source of input
>> for the cruise control.  The others were the brake switch and the
>> third was a set of magnets attached to the drive line and picked up by
>> a nearby sensor.  -That- was the speed sensor.
>>
>> The tach adapter can NOT be used as a speed sensor.  After all, you'll
>> get the same rpm in 1st gear, second gear, third, etc.  i.e. 2,000 rpm
>> in first is one speed, while 2,000 rpm in 5th is totally different.
>> You -can't- use the tach as a speed sensor.
>>
> *****Why not? The message you are sending to the cc brain is not "maintain
> 47 mph"... the message you are sending is "maintain the current speed,
> whatever it may be". If you are in 3rd at 3000 rpm, it will maintain a
> constant 30mph (for example). If you are in 5th at 3000 rpm it will maintain
> a constant 70mph. If you press the clutch to change gears, all bets are off
> and it shuts off.

One reason for tapping into the trans instead of engine rpm is to make 
sure speed is constant in case you hit "resume" in a different gear. Say 
you set the speed in 4:th, then up shift to 5:th and hit "resume", that 
might produce a surprise :-)


Thomas