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'[PICLIST] PIC:problems in driving a motor'
2000\12\25@122519 by Liew Tze Haw

picon face
l'm trying to drive a simple dc motor by using PIC. The PIC also drives some
other devices. My problem is when l try to drive a dc motor, the PIC cannot
drive other devices properly. The signal does not turn out to be the one
that l expect. All these problems did not occur before l connect it to the
motor. l cannot use relay to isolate the motor because l need to operate the
motor at a high frequency and this will spoil the relay very quickly. Do l
have any other methods or options?
Thank you.
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2000\12\25@123812 by Liew Tze Haw

picon face
Anyone knows the reason and solution to this problem?
Thank you.



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2000\12\25@124842 by David VanHorn

flavicon
face
At 05:14 PM 12/25/00 +0000, Liew Tze Haw wrote:
>l'm trying to drive a simple dc motor by using PIC. The PIC also drives some
>other devices. My problem is when l try to drive a dc motor, the PIC cannot
>drive other devices properly. The signal does not turn out to be the one
>that l expect. All these problems did not occur before l connect it to the
>motor. l cannot use relay to isolate the motor because l need to operate the
>motor at a high frequency and this will spoil the relay very quickly. Do l
>have any other methods or options?
>Thank you.


It sounds like you are asking the pic to drive the motor directly.
This will not work.  Motors draw large starting currents, and put a lot of
noise back into the supply.

If you only need to go in one direction, look at an open collector driver.
(or open-drain)  The transistor (or fet) is switched on and off by the pic,
and provides a saturated switch to ground for the motor, capable of much
more current.

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2000\12\25@134605 by Dan Michaels

flavicon
face
Liew Tze Haw wrote:
>l'm trying to drive a simple dc motor by using PIC. The PIC also drives some
>other devices. My problem is when l try to drive a dc motor, the PIC cannot
>drive other devices properly. The signal does not turn out to be the one
>that l expect. All these problems did not occur before l connect it to the
>motor. l cannot use relay to isolate the motor because l need to operate the
>motor at a high frequency and this will spoil the relay very quickly. Do l
>have any other methods or options?


http://www.epanorama.net/basics.html
http://www.epanorama.net/motorcontrol.html

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2000\12\26@161533 by Russell McMahon

picon face
>l'm trying to drive a simple dc motor by using PIC. The PIC also drives
some
>other devices. My problem is when l try to drive a dc motor, the PIC cannot
>drive other devices properly. The signal does not turn out to be the one
>that l expect. All these problems did not occur before l connect it to the
>motor. l cannot use relay to isolate the motor because l need to operate
the
>motor at a high frequency and this will spoil the relay very quickly.

You need to explain in some more detail what you are trying to do and what
the specifications of the equipment are so that people can understand your
problem and help you.

What is the motor voltage / What is the motor current / Is the power supply
able to handle the  motor load and the PIC / Does the motor work OK when
directly connected to the power supply / Has the PIC got adequate power
supply smoothing and / decoupling. / have you attempted to reduce motor
switching noise / ????? ...........


Especially -

- How many volts is your PIC power supply (5 probably???)?

- What is the rated voltage of the motor ie will it work on the PIC supply?

- If you have the PIC running correctly and then connect the motor to the
supply manually or with a switch but NOT using the PIC to control it, does
the PIC still run correctly? If not the problem is not so much PIC control
related as power supply loading or noise or ...

- Why do you need to switch the motor faster than a relay would allow?
Motors are not very responsive to very fast switching. It may be that you
are trying to control motor speed by fast on/off switching - known as "PWM"
(Pulse Width Modulation). The motor then follows the 'average" voltage.


It would be most useful if you told us what you are trying to achieve as an
end result.



regards



     Russell McMahon
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2000\12\27@113455 by Liew Tze Haw

picon face
Thanks a lot everyone!!!
Your advices had helped me a lot!!!


{Quote hidden}

5volts
>
>- What is the rated voltage of the motor ie will it work on the PIC supply?
the motor is a small dc motor and it can start to operate at small voltage,
such as 1V.
>
>- If you have the PIC running correctly and then connect the motor to the
>supply manually or with a switch but NOT using the PIC to control it, does
>the PIC still run correctly? If not the problem is not so much PIC control
>related as power supply loading or noise or ...
Yeah...it is still correct as long as the motor is not connected(or nothing
to do with) the PIC

>
>- Why do you need to switch the motor faster than a relay would allow?
>Motors are not very responsive to very fast switching. It may be that you
>are trying to control motor speed by fast on/off switching - known as "PWM"
>(Pulse Width Modulation). The motor then follows the 'average" voltage.
Actually l'm trying to use the motor to indicate different frequencies. The
limit for the relay is 1800 turns per hour and l need about 5000 turns per
hour

>
>
>It would be most useful if you told us what you are trying to achieve as an
>end result.
Thanks a lot for your advices.
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