hi guys,
thanks for the replis, just let me few days to understand and I'll get
back to you ;)
cheers
seb
--
Sébastien Lelong
Le 24 oct. 2010 à 11:03, vasile surducan <[email protected]> a
écrit :
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
>>
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