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'[PIC]: PIC reseting due to relays'
2001\08\28@144013 by Gary Neal

picon face
Hello,

       I've got a 16f870 that I'm using to turn a relay (Tyco V23105 150 mW
Nominal Coil Power, 960 ohm, 12 volt Nominal Coil Voltage) on/off.  This
relay is controlling a very small DC motor (~0.5amps).  About 10% of the
time when this relay turns on/off, it resets the PIC.  I've verified this
is what's happening.  Seems to work fine when the motor isn't connected to
the relay.  Only resets when the motor is connected.
       I'm using PORTA.0 through a resistor to turn on a 2N4401 transistor that
then powers the relay coil.  I have a 1N4004 diode across the relay
coil.  I have two 0.1uf caps on the +5v to the PIC.
       The +5v for the PIC is from a powered protoboard.  The +12v for the
transistor and relay are from a +12v battery.  The grounds of these two
power supplies are tied together.
       Can anyone help me figure out what's going on and fix this?

Thanks,

Gary

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2001\08\28@145537 by Dan Michaels

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face
Gary Neal wrote:
>Hello,
>
>        I've got a 16f870 that I'm using to turn a relay (Tyco V23105 150 mW
>Nominal Coil Power, 960 ohm, 12 volt Nominal Coil Voltage) on/off.  This
>relay is controlling a very small DC motor (~0.5amps).  About 10% of the
>time when this relay turns on/off, it resets the PIC.  I've verified this
>is what's happening.  Seems to work fine when the motor isn't connected to
>the relay.  Only resets when the motor is connected.
.......


Sounds like you need a suppressor across the relay "contacts", or
better yet at the motor itself. Since a DC motor, try a reverse
diode there or a snubber - 10-100 ohm resistor in series with a
0.1 uF cap across the motor winding. The cap should be better
quality than simple low-V ceramic. 200V or so polypropylene.

- dan michaels
http://www.oricomtech.com
========================

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2001\08\28@151216 by Dwayne Reid

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At 02:36 PM 8/28/01 -0400, Gary Neal wrote:
>Hello,
>
>Seems to work fine when the motor isn't connected to
>the relay.  Only resets when the motor is connected.

Try this:  use twisted wires going from the 12V supply to the relay, then
from the relay to the motor.  Put a 100n mono cap across the 12V supply
right at the relay.  In other words, add a bypass cap across the 12V supply
just BEFORE the relay.  Also use twisted wires from the relay to
motor.  You may also want to try putting a MOV across the motor leads,
right at the motor.

The idea here is to present a low AC impedance bypass to the noise right
where it gets generated - right at the relay contacts.  Putting a mono cap
across the motor supply right at the relay means that the noise is mostly
confined to the loop from the relay to the motor.  Using twisted wires
helps keep that noise contained to a small area.  Adding a MOV right at the
motor may help - it certainly does when the load is a large industrial
contacter or solenoid.  That huge, very fast spike that is generated when
the control relay opens gets clamped to a level that is much more easily
contained.  The same idea may hold even if the load is a motor instead of a
solenoid.

Others may suggest putting small caps right across the relay contacts -
this usually doesn't work for me.  But you can try it.

Stopping those nasty spikes is almost a black art.  Even though I've been
doing this for many years, it still often takes several attempts to get it
right.

dwayne



Dwayne Reid   <dwaynerspamKILLspamplanet.eon.net>
Trinity Electronics Systems Ltd    Edmonton, AB, CANADA
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2001\08\28@155206 by Spehro Pefhany

picon face
At 02:36 PM 8/28/01 -0400, you wrote:
>Hello,
>
>        I've got a 16f870 that I'm using to turn a relay (Tyco V23105 150 mW
>Nominal Coil Power, 960 ohm, 12 volt Nominal Coil Voltage) on/off.  This
>relay is controlling a very small DC motor (~0.5amps).  About 10% of the
>time when this relay turns on/off, it resets the PIC.  I've verified this
>is what's happening.  Seems to work fine when the motor isn't connected to
>the relay.  Only resets when the motor is connected.
>        I'm using PORTA.0 through a resistor to turn on a 2N4401
transistor that
>then powers the relay coil.  I have a 1N4004 diode across the relay
>coil.  I have two 0.1uf caps on the +5v to the PIC.
>        The +5v for the PIC is from a powered protoboard.  The +12v for the
>transistor and relay are from a +12v battery.  The grounds of these two
>power supplies are tied together.
>        Can anyone help me figure out what's going on and fix this?
>

Try a diode right across the motor terminals (assuming it only has to go in
one
direction). Obviously you want it to be reverse-biased normally.

Make sure that your 12V ground is only tied to the 5V ground at a single
point,
and preferably away from the chip on the 5V side.

What is /MCLR conected to?  Preferably tie it to a low-impedance external
BOR circuit or to Vdd.

Connect a 10 nF capacitor from C to E on the 2N4401.

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2001\08\28@170648 by Brent Brown
picon face
{Quote hidden}

Hi Gary,

It may be worth trying a 1N4148 diode in place of the 1N4004, as it
is much faster switching diode. All the suggestions so far have
been good, so figure out which one fixes the problem and then add
all the others as extra safeguards. That my 2 cents worth.

Brent Brown
Electronic Design Solutions
16 English Street
Hamilton, New Zealand
Ph/fax: +64 7 849 0069
Mobile/text: 025 334 069
eMail:  @spam@brent.brownKILLspamspamclear.net.nz

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2001\08\28@174830 by hard Prosser

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Brent
Since it only happens whaen the motor is connected I suggest you look again
at your earthing and power supply arrangements. It sounds as if you're
doing it nearly right with the 2 supplies. Is the motor supplied from the
12V also - a bit of filtering on the feed to the relay may assist. If you
are not going to be reversing the motor a diode accross it may help also -
particularly if it has field windings rather than perminant magnets.

Overall, I'd suggest making sure the earths are tied at only one point,
filtering the 12V to the relay using a 10ohm resistor and 100n cap and if
possible filtering the motor supply with at least a small inductor / cap
and possibly a diode as well.

Richard P




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{Quote hidden}

Hi Gary,

It may be worth trying a 1N4148 diode in place of the 1N4004, as it
is much faster switching diode. All the suggestions so far have
been good, so figure out which one fixes the problem and then add
all the others as extra safeguards. That my 2 cents worth.

Brent Brown
Electronic Design Solutions
16 English Street
Hamilton, New Zealand
Ph/fax: +64 7 849 0069
Mobile/text: 025 334 069
eMail:  spamBeGonebrent.brownspamBeGonespamclear.net.nz

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2001\08\28@190307 by victor Faria

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face
I had a similar problem.
ended up being the inputs were picking up noise.
so isolate inputs,try to run code with out inputs and test code.
also try software debounce on inputs.
hope this helps some.
victor

{Original Message removed}

2001\08\29@012920 by Brent Brown

picon face
Richard, just for the record, I wasn't the original poster. Good
suggestions though. I once tried all these tricks on a small DC
motor that was failing EMC compliance tests with not much luck
The answer was a series inductor in each lead to the motor and
ceramic caps to motor casing.

{Quote hidden}

Brent Brown
Electronic Design Solutions
16 English Street
Hamilton, New Zealand
Ph/fax: +64 7 849 0069
Mobile/text: 025 334 069
eMail:  brent.brownEraseMEspam.....clear.net.nz

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2001\08\29@140928 by Gary Neal

picon face
Guys,

        Just wanted to give some feedback on all the suggestions that have
been submitted.  BTW, there have been a lot of suggestions.  I appreciate
it a lot.
        I went through the suggestions and tried them.  Listed below is
what I tried and how well it worked.

1.      0.1uf cap across relay coil - no help
2.      4.7ohm resistor in series with relay coil - no help
3.      Checking all inputs for noise or floating inputs - no help
4.      10nf cap from C to E on the transistor - no help
5.      Put 0.1uf cap across relay contacts - partial success.  Instead of
failing like 75% of the time, it only failed about 10% of the time
6.      Put two 0.1 uf caps across relay contacts (in parallel) - better
partial success.  Failed probably 5% of the time.
7.      Moved the caps to the terminals right on the motor - better
success.  Failed probably 1% of the time.

        I'm saying failure is when the PIC resets or jumps to a random
place in the code.
        So, I'm thinking if I put a bigger cap on the motor winding
terminals, it will help even more.  Question is, how big of a cap should I
use?  I can't use an electrolytic b/c the motor reverses direction.  Anyone
have a suggestion?  Hopefully something fairly cheap.

Thanks,

Gary


At 02:55 PM 8/28/01 -0400, Dan Michaels wrote:
{Quote hidden}

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2001\08\29@142541 by Quentin

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face
Gary Neal wrote:

> 7.      Moved the caps to the terminals right on the motor - better
> success.  Failed probably 1% of the time.
>
>          I'm saying failure is when the PIC resets or jumps to a random
> place in the code.
>          So, I'm thinking if I put a bigger cap on the motor winding
> terminals, it will help even more.  Question is, how big of a cap should I
> use?  I can't use an electrolytic b/c the motor reverses direction.  Anyone
> have a suggestion?  Hopefully something fairly cheap.
We in the electric R/C world always put caps on the terminals (10n).
What we also do is to connect a cap from each terminal to the metal body
of the motor as well.

Quentin

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2001\08\29@143613 by Douglas Butler

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face
Try keeping the cap on the motor (or two caps to the motor frame) and
add two "hash chokes" (Digi-Key #M5252-ND or simillar) in the motor
leads near the motor.  A hash choke is basically a low Q, high current,
moderate inductance coil intended to stop EMI.

Sherpa Doug

> {Original Message removed}

2001\08\29@144412 by Barry Gershenfeld

picon face
I think you are getting closer to the solution.  You've shown
that working at the motor seems to help the most.

Remember that bigger capacitors that are rolled or folded inside
have an inductance, meaning that sometimes smaller simpler capacitors can
bypass the highest frequencies better.  In some cases a combination is
warranted.

Don't just keep making the caps bigger, try some of the other
ideas in addition to the caps.

Barry

At 02:05 PM 8/29/01 -0400, you wrote:
{Quote hidden}

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2001\08\29@155430 by Dan Michaels

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face
Gary Neal wrote:
...........
>7.      Moved the caps to the terminals right on the motor - better
>success.  Failed probably 1% of the time.
>

Good to hear things are coming along. You might try small R's
[10-100 ohms] in series with the caps, since you will get a
current surge into the cap during relay contact closure otherwise.
You get L di/dt [from motor] at contact opening and C dv/dt
[from cap] at closure.

Also, as others mentioned, if the caps are too big the sol'n
is self-defeating due to series inductance/etc. Effective
snubbers for switching "amp" loads at 220VAC usually use no
more than 0.1 uF or so - but they usually have series R's too.

If using separate motor gnds and also snubber at the motor
doesn't do the trick, then you may need to go in and strenghten
spike rejection circuitry throughout the entire conotroller. I
have been involved in this sort of thing, and sometimes it
takes appropriate components placed in "many" places before
the system is reliable.

BTW, are your current 1% failures occurring at relay "closure"
or "opening" ?????

- dan michaels
http://www.oricomtech.com
========================

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2001\08\29@181817 by Jinx

face picon face
I've had a similar problem with a PIC controlling a ticket
dispenser. The cause was a string of 1us pulses reaching
Mclr as the motor turned. The solution was to isolate the PIC
from the motor's supply using a 100 ohm resistor with 470uF
+ 22n cap next to the PIC and decreasing the Mclr pull-up
to 1k as well as increasing the Mclr cap to ground to 1uF

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2001\08\29@195955 by Jinx

face picon face
part 1 282 bytes content-type:text/plain; (decoded 7bit)

A couple of people asked me off-list what I meant. Attached
is a gif from my notes at the time. The opto and motor caps
were already built in to the ticket mechanism. It also had an
opto for the inter-ticket holes which the PIC used for counting


part 2 2633 bytes content-type:image/gif; (decode)


part 3 105 bytes
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2001\08\29@202514 by Brent Brown

picon face
Jinx,

I noticed that you do not have a series resistor into the MCLR pin
when using a capacitor like Mchip suggests. Not sure I actually
understand their reasoning on this anyway, any comments?

> A couple of people asked me off-list what I meant. Attached
> is a gif from my notes at the time. The opto and motor caps
> were already built in to the ticket mechanism. It also had an
> opto for the inter-ticket holes which the PIC used for counting


Brent Brown
Electronic Design Solutions
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Hamilton, New Zealand
Ph/fax: +64 7 849 0069
Mobile/text: 025 334 069
eMail:  @spam@brent.brown@spam@spamspam_OUTclear.net.nz

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2001\08\29@210751 by Olin Lathrop

face picon face
> 1.      0.1uf cap across relay coil - no help
> 2.      4.7ohm resistor in series with relay coil - no help
> 3.      Checking all inputs for noise or floating inputs - no help
> 4.      10nf cap from C to E on the transistor - no help
> 5.      Put 0.1uf cap across relay contacts - partial success.  Instead of
> failing like 75% of the time, it only failed about 10% of the time
> 6.      Put two 0.1 uf caps across relay contacts (in parallel) - better
> partial success.  Failed probably 5% of the time.
> 7.      Moved the caps to the terminals right on the motor - better
> success.  Failed probably 1% of the time.
>
>          I'm saying failure is when the PIC resets or jumps to a random
> place in the code.
>          So, I'm thinking if I put a bigger cap on the motor winding
> terminals, it will help even more.  Question is, how big of a cap should I
> use?  I can't use an electrolytic b/c the motor reverses direction.
Anyone
> have a suggestion?  Hopefully something fairly cheap.

Trying to reduce the noise at the source like you are doing is reasonable.
However, you should also try to make your circuit immune to the noise.  Make
sure you have a good ground plane under the PIC and put bypass caps as close
as possible to each power lead.  It sounds like high frequency noise is
making it back to your 5V power supply.  You may also have a ground spike
between the PIC and wherever its I/O lines are going.  In that case, beaf up
the ground conductor and put small series resistor on the PIC lines.  To go
further, you could also put some clamping on the lines.  Whether this is
acceptable depends partially on whether you can tolerate slower edeges and
what the lines are driving, etc.


********************************************************************
Olin Lathrop, embedded systems consultant in Littleton Massachusetts
(978) 742-9014, .....olinspam_OUTspamembedinc.com, http://www.embedinc.com

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2001\08\30@022033 by Dan Michaels

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face
At 12:00 PM 8/30/01 +1200, you wrote:
>A couple of people asked me off-list what I meant. Attached
>is a gif from my notes at the time. The opto and motor caps
>were already built in to the ticket mechanism. It also had an
>opto for the inter-ticket holes which the PIC used for counting
>
>Attachment Converted: C:\WIN31APP\EUDORA\ATTACH\ticket.gif
>

I hate to be a poop, Captain.J, but you are not supposed to
tie a big cap straight into the /Mclr pin. [need I explain?]

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2001\08\30@031238 by Jinx

face picon face
> I hate to be a poop,

Only you know that for sure. Pick one for your conscience

(a) Dan Michaels = A damn chisel

(b) I'm Dan Michaels = A calm dim shine

Try it with mine (ha ha, good luck with the J and Q)

> but you are not supposed to tie a big cap straight into
> the /Mclr pin

Is 1uF really that big ? I recall others on the list who routinely
use 10uF or more with no apparent problem. As I said, my
usual is 10n + 10k

[need I explain?]

ooookay, you got some 'splainin' to do Lucy

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2001\08\30@082758 by Olin Lathrop

face picon face
> Is 1uF really that big ?

Yes, I definitely wouldn't do this.  When power is shut off and the power
supply drops, the cap will discharge thru the PIC.  The cap current is I = C
* dV/dt = 1uF * 5V / Td,
where Td is the power supply discharge time in seconds.  If your supply
discharges in 5mS then the average cap current will be 1mA.  If the PIC
doesn't allow that current, then you enter unspecified territory with MCLR
at 5V and everything else at 0.

> I recall others on the list who routinely
> use 10uF or more with no apparent problem.

Now you get 1mA average at 50mS discharge time.


********************************************************************
Olin Lathrop, embedded systems consultant in Littleton Massachusetts
(978) 742-9014, TakeThisOuTolinKILLspamspamspamembedinc.com, http://www.embedinc.com

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2001\08\30@082808 by Olin Lathrop

face picon face
> A couple of people asked me off-list what I meant. Attached
> is a gif from my notes at the time. The opto and motor caps
> were already built in to the ticket mechanism. It also had an
> opto for the inter-ticket holes which the PIC used for counting

I noticed the motor is used in one direction only but has no flyback diode
around it.  This may have been part of what was causing your glitches.  The
100nF caps slow down and reduce the peak voltage of the flyback pulse, but I
think the transistor is still taking a beating.


********************************************************************
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(978) 742-9014, .....olinspamRemoveMEembedinc.com, http://www.embedinc.com

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2001\08\30@124742 by Douglas Butler

flavicon
face
Note that if you accidentally short the power supply by dropping a
screwdriver on it, the dV/dt will be very high.

Sherpa Doug

> {Original Message removed}

2001\08\30@125509 by Spehro Pefhany

picon face
At 12:36 PM 8/30/01 -0400, you wrote:
>Note that if you accidentally short the power supply by dropping a
>screwdriver on it, the dV/dt will be very high.

Yes. Whether you wish to cover that case by adding extra parts is
probably application-specific.

Best regards,
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2001\08\30@170402 by Jinx

face picon face
> > Is 1uF really that big ?
>
> Yes, I definitely wouldn't do this

OK, I'm sold. From now on I'll add series R. The F87x pdf
I have has no circuit suggestion and no special comments
about Mclr (that I can see anyway). Is it the same as the
F84A ?

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2001\08\30@181509 by Jinx

face picon face
> > opto for the inter-ticket holes which the PIC used for counting
>
> I noticed the motor is used in one direction only but has no
> flyback diode around it.  This may have been part of what
> was causing your glitches.  The 100nF caps slow down and
> reduce the peak voltage of the flyback pulse, but I think the
> transistor is still taking a beating

I couldn't swear to the fact there was no flyback diode. The
dispenser was a ready-made module and I made the best
notes I could without dismantling it. Aside from that though,
the carnival game this was part of was a rifle range using
flash tubes in the guns. A trigger-operated circuit dumped
450VDC into the flash tubes, which caused quite an electronic
ruckus. So even if the motor had been clean, the micro still
needed protecting

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2001\08\30@200748 by Brent Brown

picon face
> > > Is 1uF really that big ?
> >
> > Yes, I definitely wouldn't do this
>
> OK, I'm sold. From now on I'll add series R. The F87x pdf
> I have has no circuit suggestion and no special comments
> about Mclr (that I can see anyway). Is it the same as the
> F84A ?

In the F87x case I suspect the ICD might have problems with a cap
on MCLR. Can't say why exactly, just a gut feeling...

Brent Brown
Electronic Design Solutions
16 English Street
Hamilton, New Zealand
Ph/fax: +64 7 849 0069
Mobile/text: 025 334 069
eMail:  spamBeGonebrent.brown@spam@spamspam_OUTclear.net.nz

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2001\08\30@235229 by Dan Michaels

flavicon
face
At 09:04 AM 8/31/01 +1200, you wrote:
>> > Is 1uF really that big ?
>>
>> Yes, I definitely wouldn't do this
>
>OK, I'm sold. From now on I'll add series R. The F87x pdf
>I have has no circuit suggestion and no special comments
>about Mclr (that I can see anyway). Is it the same as the
>F84A ?
>

Get the latest d/s, see fig 12-6 - [fig missing from 1st
d/s, present in last 2 versions].

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2001\08\31@022546 by Jinx

face picon face
> Get the latest d/s, see fig 12-6 - [fig missing from 1st
> d/s, present in last 2 versions].

The Reset section of the mid-range manual is more
up-to-date than the specific F628 manual I got not all
that long ago. It does make some points not in older
references, but the full story still isn't there in one place.
Sheesh. Still, what the hell

www.microchip.com/0/lit/pline/picmicro/refernce/midrange/midsect/3100
3a/index.htm

"Better be ignorant of a matter than half know it" - Plubilius Syrius

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2001\08\31@115003 by Dan Michaels

flavicon
face
At 06:09 PM 8/31/01 +1200, you wrote:
>> Get the latest d/s, see fig 12-6 - [fig missing from 1st
>> d/s, present in last 2 versions].
>
>The Reset section of the mid-range manual is more
>up-to-date than the specific F628 manual I got not all
>that long ago. It does make some points not in older
>references, but the full story still isn't there in one place.
>Sheesh. Still, what the hell
>
>www.microchip.com/0/lit/pline/picmicro/refernce/midrange/midsect/3100
>3a/index.htm
>
>"Better be ignorant of a matter than half know it" - Plubilius Syrius
>

If you're speaking of the basic info re weakness at the /Mclr pin
in PICs, it is present in my '95 Mchp databook. It just happened
to be left out of the "1st" version of the 'F87x d/s, but is present
in later versions. Mchp has known of this issue for years.

The figure also is left out of 'F628 d/s I have dated 12/09/99.

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