You can use a reed relay for this pupose. It's cheap!

thanks
Riaz

Des Bromilow wrote:

> Is it worth building soemthing based on exisitng speedo ideas?
>
> a rotating magnet pulls the needle against a spring..
>
> Why not use the rotating magnet to generate pulses, or to generate an average
DC voltage (which could be fed into a PLL VCO)
>
> Just batting ideas around.
>
> Des
>
> >>> Wagner Lipnharski <wagnerl@EARTHLINK.NET> 7/13/99 12:32:07 am >>>
> Does anyone knows some supplier for "speed transducer" to be installed
> at the car speedometer cable?
> My circuit needs to receive a frequency proportional to the car speed,
> and I need to find out ... well... cheap sensors... :)
>
> Thanks
> Wagner Lipnharski
> http://www.ustr.net