Jinx,
It shouldn't be too hard to chop into AC, amplify, feed a transformer,
rectify and then voltage divide for feedback to make linear..

Say a simple oscillator, a mux or gate circuit, an audio amp, a
transformer, a couple of diodes and a few resistors & caps etc.

If you have to use a PIC, you could make a simple voltage booster,
again using a voltage divider to feed back and linearise the response.
The PIC could be the oscillator and handle the ADC work etc and a
bipolar or small FETs to drive the boost choke..

RP

2009/11/24 Jinx <joecolquitt@clear.net.nz>:
> I've got a friend (yes, really) who has an old vehicle dynamometer. At
> the moment he uses a DC tacho generator attached to the floor roller
> which puts out 8V per 1000rpm into the dynamometer, up to a limit
> of 6000rpm. Doing it this way means the feedback is speed
>
> He's wanting to use a dashboard tacho, to use rpm feedback, an
> example of which he has and thinks puts out 1V per 1000rpm. The
> active component is an SAK215
>
> http://www.datasheetcatalog.com/datasheets_pdf/S/A/K/2/SAK215.shtml
>
> The meter in this dash tacho is presumably a 10mA movement
>
> What he's asked me to do is amplify the 0 - 6V (ie 0 - 6000rpm) range
> of the dash tacho to 0 - 48V to feed to the dynamometer
>
> One thought I have is to boost the 12V car supply to 48V with an SMPS,
> and use a PIC to measure the voltage from the tacho and chop/integrate
> the 48V to 8x that voltage
>
> I think opamps are out because of the 48V, but would consider any
> other linear suggestions anyone has, perhaps a modified audio amp
> for example
>
> TIA, wbr
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