Hi Kiste, 2010/11/12 Oliver Seitz <[email protected]>
> Hi Seb, > finally took the time to have a look at the schematics... > And, finally yahoo allows me to send mails to the list again a bit more > regularly... ;-) > > >>Something in between. I'm using 1% accurary resistors: > http://sirbot.org/sirbot-modules/dc-motor-controller-board/dcmc_rctank_schematic.png > > To be honest, the resistors shouldn't do anything bad. I think you don't > really want to _measure_ the voltage, but compare it to some previous > values. So the resistor tolerances, together with the motor characteristics, > are stored in your reference values. > I'm not sure, measuring the voltage allows me to deduce motor's speed. > >> Is there a dedicated 5V reference, or do you simply use one supply to > power different devices? Then your reference voltage could introduce errors > of several percents. > >Vref is the one used by the PIC itself. So yes, it may be shared with > other devices (but not the motors') > > The board has its own linear regulator, that's not bad for a start :-) > Switching power supplies are good for computers, but not as reference > voltage for measurements. But, if it's a 7805 or the like, remember that it > outputs _about_ 5V. Each 7805 has its own voltage... And it changes over > temperature. It's good for power, but not for reference. Yes this is a 7805. And indeed every has its own voltage output... Not good ! > A cheap way would be something like LP2950CZ, a higher-precision voltage > regulator that has a quite good accuracy when loaded very little, or a true > voltage reference like from the LT1021 series, but those do cost money. > OK, thanks I will keep this in mind (LP2950). > > Just for theory... I don't think you'll need anything of this to find out > if your motor is stuck :-D > Talking about theory, I tried to simulate what we talked about before, with op-amps, etc... following the schematic you provided (hand maded), adjusting some values. This was to understand the theory. I used KTechlab (nice, http://en.wikipedia.org/wiki/KTechlab), but I couldn't any coherent results :) I must have done something wrong, I'll get back soon. Do you know any other free tools used to simulate electronic components ? Cheers, Seb -- You received this message because you are subscribed to the Google Groups "jallib" group. To post to this group, send email to [email protected]. To unsubscribe from this group, send email to [email protected]. For more options, visit this group at http://groups.google.com/group/jallib?hl=en.
