At 04:13 AM 24/11/2009, you wrote:
>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

Maybe you could do this with an LM2577, a TLV431 and an ordinary op-amp
(eg. 1/2 LM358)-- the latter two parts to modify the feedback path to
include an offset and include a negative term proportional to the 
input voltage.

>Best regards,

Spehro Pefhany --"it's the network..."            "The Journey is the reward"
speff@interlog.com             Info for manufacturers: http://www.trexon.com
Embedded software/hardware/analog  Info for designers:  http://www.speff.com



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