On Tue, Nov 24, 2009 at 4:13 AM, Jinx 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 You could use an LM3875, I think you could get it to work in single-supply fashion. It can also handle the current easily. It does get warm in quiescent conditions. -- Martin K. -- http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist