read engine rpm from battery/alternator???

[Peter D. Hipson]

Yes it is possible. With the scope, you may need to use an isolating cap.
Several tachs do this, especially those for diesel engines, which are a
pita. Some alternators (GM?) have an A/C output terminal just for this
purpose. 

At 02:55 PM 6/19/99 +0200, you wrote:
>Recently I´ve seen that Bosch´s latest rolling road reads the engine rpm
from 
>the battery voltage. When connecting my multimeter to the battery I can read 
>different frequencies at different rpm´s caused by the alternator. This
seems to 
>be easy but when connecting my 20 MHz-oscilloscope to the battery I can
only see 
>a flat line around 14.0 volts. 
>
>Does anybody know how I can read the rpm from the battery using a 
>microcontroller like PIC or Basic Stamp II?
>
>Kind regards 
>
>Alex Wenning
>
>------------------------
>e-mail:	mail at wenning.de
>
>website: www.wenning.de
>------------------------
>
>
>
Thanks, 
        Peter Hipson (founder, NEHOG)
        1995 White NA Hummer Wagon