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'[PICLIST] [PIC] problems in driving a motor'
2000\12\25@130751 by Herbert Graf

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> 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?

    From what you are writing it sounds like you are driving the motor
directly from the PIC. Unfortunately you cannot do that, motors require alot
of current (especially at startup and stalls) and put ALOT of noise on every
line connected to it. It doesn't sound like you need the motor to reverse. I
recommend using a transistor as your driver, if it is a small motor a 2N2222
or 2N3904 would be fine. TTYL

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2000\12\26@131938 by Liew Tze Haw

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>      From what you are writing it sounds like you are driving the motor
>directly from the PIC. Unfortunately you cannot do that, motors require
>alot
>of current (especially at startup and stalls) and put ALOT of noise on
>every
>line connected to it. It doesn't sound like you need the motor to reverse.
>I
>recommend using a transistor as your driver, if it is a small motor a
>2N2222
>or 2N3904 would be fine. TTYL
>

Do l need a separate power supply(battery) for the transistor? l tried the
method above by using the same power supply(with the rest of the circuits)
but it still cannot work well. l don't know what is the reason for this.
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2000\12\26@133221 by David VanHorn

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>
>Do l need a separate power supply(battery) for the transistor? l tried the
>method above by using the same power supply(with the rest of the circuits)
>but it still cannot work well. l don't know what is the reason for this.

You may be crashing your power supply.
Try it with a separate supply, like AA batteries, for the motor.
In this case, series the batteries to get the proper voltage, and connect
the motor to the + battery lead. Connect the other motor lead to the
transistor's collector, and connect the transistor's emitter to the battery
- lead.

Connect a diode (1N4001 or similar) across the motor, with the banded end
connected to the battery + lead, and the other end to the transistor collector.

Connect the battery - lead also to the processor's ground, and connect the
transistor's base through a 1k resistor, to the appropriate port pin.

The 1k may need to be adjusted, it's just a guess.


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2000\12\26@134304 by Dan Michaels

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Liew Tze Haw wrote:
>>      From what you are writing it sounds like you are driving the motor
>>directly from the PIC. Unfortunately you cannot do that, motors require
>>alot
>>of current (especially at startup and stalls) and put ALOT of noise on
>>every
>>line connected to it. It doesn't sound like you need the motor to reverse.
>>I
>>recommend using a transistor as your driver, if it is a small motor a
>>2N2222
>>or 2N3904 would be fine. TTYL
>>
>
>Do l need a separate power supply(battery) for the transistor? l tried the
>method above by using the same power supply(with the rest of the circuits)
>but it still cannot work well. l don't know what is the reason for this.


You have to break this problem apart, figure out what is happening
with the individual pieces, and only then put the pieces back
together.

1. Determine what it takes to run the motor all by itself. Run it
off a variable power supply, or from C- or D-cells directly. First,
1 cell, then 2 cells, etc. Determine what seems to operate the
motor best.

2. If the motor takes some voltage other than 5v and 25mA, which is
a leadpipe certainly, then you cannot run it directly off the PIC,
and have to build a driver ckt, as Dave said.

3. Build the driver ckt all by itself, get the motor running, and
only then think about connecting it to your PIC.

This is how an engineer attacks a problem like this.

good luck,
- danM

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2000\12\26@142657 by Herbert Graf

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> >      From what you are writing it sounds like you are driving the motor
> >directly from the PIC. Unfortunately you cannot do that, motors require
> >alot
> >of current (especially at startup and stalls) and put ALOT of noise on
> >every
> >line connected to it. It doesn't sound like you need the motor
> to reverse.
> >I
> >recommend using a transistor as your driver, if it is a small motor a
> >2N2222
> >or 2N3904 would be fine. TTYL
> >
>
> Do l need a separate power supply(battery) for the transistor? l tried the
> method above by using the same power supply(with the rest of the circuits)
> but it still cannot work well. l don't know what is the reason for this.

    You might. You have to break down the problem and determine what is
happening. Try looking at the supply lines with an O-Scope when the motor
turns on, are there any spikes or noise present? What you could try is
connecting the motor to a separate supply, if this fixes your problems you
know it is a supply problem. One easy solution is to put a small resistor in
series with the PIC's supply line and a small and large capacitor in
parallel with the PIC's power supply lines. This sort of isolates the PIC
from the rest of the world since the caps will fill in momentary drops in
supply. Also, try putting a diode (the type of diode depends on your motor,
you may be able to get away with a 1N4003 or similar) across the terminals
of the motor in reverse of the polarity of the electricity supplying the
motor. This will damp out reverse voltages created when the motor is
disturbed (turned off, stalled, etc).
If a separate supply doesn't solve your problem the EMI generated by the
motor might be bleeding into the PIC. This is a much more difficult problem
to solve, optoisolation might help. How big is the motor? (how much does it
draw, what speed, etc.) Hope this helped. TTYL

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