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? 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]. >> 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. > -- 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.
