feedback,
And the magnets will vary in strength over temperature.
I understand that there are also PWM driver circuits that read the motor voltage when the driver amp is high impedance, basically using the motor as a tachometer. This doesn't solve the magnet's variance with temperature, but that's not a big issue normally.
I haven't tried it, but someday...
wart
feedback,
Now that you mention it, I remember the trick of reading the back EMF.
However, where does the current go ?:-)
Then there's EC motor (electronically commutated) controllers like I designed for Bosch. The speed is a function of the clock rate.
I still have one of their motors here that is as big as an alternator ;-)
...Jim Thompson
Jim Thompson sez:
A straightforward solution.
What is U1? Any op-amp?
Is Rext chosen to be the same R as the motor?
To make speed variable, should R1 be replaced with variable?
That's OK. I think that speed regulation is not so critical. The goal is to be able to adjust full range. If it's noticed that speed has changed due to thermal reasons, can easily be manually adjusted. It should settle down once motor has warmed...
If you would be so kind... (c:
Thanks,
In article , Jamie wrote: [....]
Don't forget the diode on the motor to eat the spike as the MOSFET turns off.
If you run the pin 5 of the 555 to a zener, you can compensate for the variations in the input voltage.
"John E." skrev i meddelandet news: snipped-for-privacy@news.sf.sbcglobal.net...
wart
feedback,
JT
Either an OpAmp with enough power capability to run the motor directly, or an OpAmp with a boost transistor added at the output.
Yes.
No, VC is the "command"
...Jim Thompson
In that case, from now on I will be suggesting the use of AVRs! I wouldn't want to be a "troll".
More seriously ... while I agree that using a uC to generate an unvarying square wave is overkill, I think you're diluting the term "troll" into meaninglessness ... it doesn't just mean "someone who posted something I don't agree with", you know.
Actually, the uC approach might not be so silly. DigiKey shows about the same prices for PIC10F200s as for 555s, and the PIC would require fewer external components (after programming, of course). Ditto the ATtiny11 and some of the Zilog Z8s. Sheesh!
LM317, a pot, & a couple of resistors should do the trick easily & cheaply. Suitable circuits can be found on most LM317 data sheets.
Take a look at the links here
That's not good. Every problem must be solved by a circuit using either an LM555 or a PIC, perferably both :>
Earlier, I suggested the LT1083 as a better way to go than the LM317 because of the heat issue. I have also thought of a very ugly circuit like this:
Input +V ------+------------------+----------------+----- To motor ! ! ! ! \\ ! ! / --- ! -- \\ --------- ^ ! ! ! ! ! ! --- +---/\\/\\---++----+----- To motor ! --- ! ! \\ ! !/e ! /
Hey, LM317s are /nearly/ as traditional an answer to any kind of electronics problem as the classic 555, & much more traditional than those new-fangled PICs. ;) (And my science teacher in highschool used LM3909 as his solution for most things.)
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