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]. For more options, visit this group at http://groups.google.com/group/jallib?hl=en.
