On Sun, Oct 24, 2010 at 1:58 AM, Joep Suijs <[email protected]> wrote:
> Hi Vasile, > > If this is the case, put in a voltage divider for motors up to 25V and > you can cope with motors from 5 to 25V, right? > right :) > Below 5V probably makes no sense. All 3V motor I've seen are so bad > that I doubt you can do anything with back-EMF. > > Joep > > 2010/10/24 vasile surducan <[email protected]>: > > Hi Joep, > > What I understood is that he want to use different motors and offer a > > software pack which does not need hardware acknowledges for > recalibration. > > That's possible with a fixed divider and some software (ADC, software > > controlled divider, programmable controlled current source or whatever). > In > > my opinion even an 8 bit ADC can do this trick, the problem is one motor > > gives him 25V and the other 10V EMF... A hobby user take the motor from > the > > junkbox, one is 3V but supplied at 5V, one is 12v but supplied at 5V too. > I > > guess this is the problem he want to avoid. > > Vasile > > > > On Sun, Oct 24, 2010 at 1:43 AM, Joep Suijs <[email protected]> wrote: > >> > >> Hi All, Seb, > >> > >> What you state is that 10 bits of resolution are required for 5v > >> motors (5mV steps). Is that right? > >> When you create a 25V range, you end up with 25mV steps with 10bits. > >> Is this realy to inaccurate? If I understand correct, back-EMF gives > >> you the voltage proportional to the rotation speed of your motor. If > >> you have a 5V motor at top speed, it will give you (almost) 5V. If you > >> measure in 25mV steps, you get the motor speed in 200 steps (probably > >> 100 steps forward speed and 100 backward). I would expect this > >> measurement is more accurate than the methode itself? > >> > >> But if you realy do need this accuracy, you could take a 12bit adc and > >> get 6mV steps over the whole range. So this is one way to go. I agree > >> it is probably a bit more expensive, but probably easier and more > >> stable than adding a few resistors, transistors and opamps. > >> > >> But an other way is combining multiple measurements. Your average > >> signal is the motor speed, which changes slow compared to the adc > >> speed. And since your signal is quite noise, you need more samples > >> anyway. And more samples on a noisy signal mean more resolution. > >> > >> Bottom line: you might be solving a problem that does not make any > >> (much) difference in a real life app... > >> > >> Joep > >> > >> -- > >> 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]<jallib%[email protected]> > . > >> For more options, visit this group at > >> http://groups.google.com/group/jallib?hl=en. > >> > > > > -- > > 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]<jallib%[email protected]> > . > > For more options, visit this group at > > http://groups.google.com/group/jallib?hl=en. > > > > -- > 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]<jallib%[email protected]> > . > For more options, visit this group at > http://groups.google.com/group/jallib?hl=en. > > -- 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.
