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'[EE:] Release of magic smoke'
2004\02\27@024308 by Gustaf J. Barkstrom

picon face
One of my 16F84A's just died after some high duty-cycle running of stepper
motors.  The circuit I built is basically the one found at the bottom of
this page: http://www.dakeng.com/u2.html Source code is also available on
that page.

However, I buffered the inputs of the PIC with a 74LS244 (octal line
driver), and used a Darlington array (ULN2803) on the outputs to drive the
steppers instead of the discretes shown in the schematic.  Note also that I
am not using a resistor between the PIC output pins and the Darlington array
input pins.

An ASCII block diagram of my circuit:

[parallel port data pin] -> [74LS244] -> [PIC] -> [ULN2803] -> [Stepper]

The entire circuit, including motors, is using the same 5+/GND regulated
power supply. PIC is RC clocked, and the power/gnd pins are not bypassed on
either the PIC or the line buffer/drivers.  Pin 3 of the PIC floats, as
the page linked above says "leave this pin floating if you like."

I ran two steppers (Vexta 2-phase, 5V/1A nominal) on this circuit for
several minutes, but no more than 30 seconds at a shot.  So, I got brave and
told my software to run the motors over a long distance, and they ran
continuously for about 4 minutes. After that, the chip froze (motors
stopped); held MCLR low and released it high again, still nothing.  I
touched the top of the Darlington arrays and the buffer/drivers, barely
warm.  I touched the PIC and about got a 2nd degree burn.

I turned everything off, went to bed, and turned it back on the next day.
Normally, the motors lock into an initial position at power-up, but now no
power is going to either of them.  Before I troubleshoot further, I would
like to get some input on the flaws of my circuit.  PCB art and schematics
available at your request, if the flaws of the circuit are not already
blatently obvious...

I think (in a sophomoric way) that my question is: why is so much current
going through the PIC?

By the way, the circuit worked very well until I turned up the duty-cycle.

Thanks,

Gustaf

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2004\02\27@040127 by Joe McCauley

picon face
Have you tied pin 10 (the output diode common ) to the supply voltage
for the motors? If not then maybe back emf from the motor coils have
killed the PIC.

Joe

{Original Message removed}

2004\02\27@063504 by cisco J. A. Ares

flavicon
face
Gustaf J. Barkstrom wrote:

>Note also that I
>am not using a resistor between the PIC output pins and the Darlington array
>input pins.
>
>
>
>
This may be the problem, PIC output pin logic low level is close to 0,
so this is ok, but the logic high is 5V (for a critical example) and VBE
is close to 1V on darlingtons.

Hope this helps
Francisco

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2004\02\27@064748 by Rick C.

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face
Was there a reason for not providing bypass and spike protection for the PIC?
Rick

"Gustaf J. Barkstrom" wrote:

> One of my 16F84A's just died after some high duty-cycle running of stepper
> motors.

> The entire circuit, including motors, is using the same 5+/GND regulated
> power supply. PIC is RC clocked, and the power/gnd pins are not bypassed on
> either the PIC or the line buffer/drivers.

> I touched the PIC and about got a 2nd degree burn.
>

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2004\02\27@070031 by Roland

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face
The 2803 has a 2K7 series resistor on the input, so that should be OK.
Whats more likely happening is that flyback from the stepper coils is
causing the 5V to spike, and the pic is doing the clamping!

try and use separate supplies, as shown in the diagram, or adequately
isolate the two regions, logic and power.

Regards
Roland


At 02:45 AM 27/02/04 -0500, you wrote:
{Quote hidden}

Regards
Roland Jollivet


JeM Electric cc
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2004\02\27@093033 by Gustaf J. Barkstrom

picon face
Roland and all,

Okay, I don't feel too stupid now.  I was going to post
a question about separate power supplies, but then this
happened.  So, here's my question about power supply
separation:  Where is the separation?  What I mean is,
I understand using two areas of the board, but do I need
two wall-warts, two regulators, etc?  Do I have to separate
them back up to mains AC?

Yes, I chose the ULN2803A because it has the 2.7k resistors
on input; the datasheets say this is specifically for
5v TTL/CMOS connection, so I thought I was good on inputs.

Again, I'm using a 15V Zener to pin 10 (common) on the ULN2803
to prevent back EMF.  Is that sufficient?

Thanks again,

Gustaf

> {Original Message removed}

2004\02\27@093441 by Gustaf J. Barkstrom
picon face
As for my omission of bypass caps, that was lack of experience.

I did provide what I thought was back EMF spike protection using
a 15V zener diode to the common supply pin of the ULN2803, but I
forgot to mention this in my initial post. :(

Is a single zener sufficient or appropriate?

Thanks again,

Gustaf

> {Original Message removed}

2004\02\27@093858 by Gustaf J. Barkstrom

picon face
Indeed, but as Roland posted later today, there's a 2.7k resistor
on each of the darlington's inputs in the ULN2803, and that's
why I chose that chip.

Here's a question though: the code places TRISA and TRISB as I recall,
which causes the output pins to have high impedence off state to my
understanding; so, "collector-emmitter" current from the darlingtons
wouldn't be pushing into the off-state PIC output pins, right?
I hope that question made sense, but forgive my complete lack of
recollection of transistor operation. :(

Thanks,

Gustaf

> {Original Message removed}

2004\02\27@094723 by Gustaf J. Barkstrom

picon face
Joe,

Oops, I forgot to mention this in my post.  Yes, I used a 15v zener
diode "pointing towards" the common pin (pin 10) of the darlington
to spike-protect from back EMF.  Is that sufficient and/or appropriate?

By the way, "pointing towards" is what a mechanical guy like me says
because I can't remember which is anode and cathode (ugh!).  I'll beat
that into my brain before I'm done. :-)

My new design separates the power supplies, but see my
earlier post today about how/where to separate them, as I'm not sure
where to do that.

Thanks,

Gustaf

> {Original Message removed}

2004\02\27@100147 by hael Rigby-Jones

picon face
>-----Original Message-----
>From: Gustaf J. Barkstrom [.....gustaf.bKILLspamspam@spam@COX.NET]
>
>Oops, I forgot to mention this in my post.  Yes, I used a 15v
>zener diode "pointing towards" the common pin (pin 10) of the
>darlington to spike-protect from back EMF.  Is that sufficient
>and/or appropriate?
>
>By the way, "pointing towards" is what a mechanical guy like
>me says because I can't remember which is anode and cathode
>(ugh!).  I'll beat that into my brain before I'm done. :-)
>

Easy way to remember this, look at the diode symbol and you will see that
part of it forms a K, which stands for Kathode.  Just remember not to spell
it like that when you write it :)

i.e.

(K)athode  Anode
---------|<------

Regards

Mike




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2004\02\27@101603 by cisco J. A. Ares

flavicon
face
I use to put a schotky (not sure about spelling) diode for spike
protection, cathode to positive.

Francisco


Gustaf J. Barkstrom wrote:

{Quote hidden}

>>{Original Message removed}

2004\02\27@102014 by Spehro Pefhany

picon face
At 02:45 AM 2/27/2004 -0500, you wrote:

>I think (in a sophomoric way) that my question is: why is so much current
>going through the PIC?

It's called latch-up and results from current going through the on-chip
protection diodes (too much current) which triggers the GIANT PARASITIC
SCR which lives inside every PIC, right across the power supply. This
is essentially a self-destruct if your power supply has enough juice. The
SCR triggering itself is non-destructive, but the resulting current causes
enough heating to damage or destroy the chip.

>By the way, the circuit worked very well until I turned up the duty-cycle.

It was probably marginal.

I suspect your problem is one of circuit layout. You must not allow
motor current to flow between the ground pin on the darlington array
and the Vss pin on the PIC. IOW if you think of a "star" connection
at the ground of the power supply, one point goes off to the PIC
and one goes off to the ULNxxxx ground. You do NOT ground the PIC
to the supply and run the connection from there to the ULNxxx (although
the opposite would be okay). There should be a BFC (electrolytic)
paralleled with a 0.1 ~ 1uF ceramic close to the PIC and the motor
from ground to Vdd/5V. 1000uF 6.3V low impedance (like you
find on a PC motherboard) works fine.

BTW, you might want to put a 1K on each PIC output. Yes, there's a
resistor inside the ULNxxx, but trust me. There's also an isolation
junction diode to the substrate...

The zener on the catch diodes is just fine, provided it doesn't get too warm.

Best regards,

Spehro Pefhany --"it's the network..."            "The Journey is the reward"
.....speffKILLspamspam.....interlog.com             Info for manufacturers: http://www.trexon.com
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2004\02\27@102433 by Joe McCauley

picon face
Tie pin 10 to the positive supply of the motors directly.

Joe

-----Original Message-----
From: pic microcontroller discussion list
[EraseMEPICLISTspam_OUTspamTakeThisOuTMITVMA.MIT.EDU] On Behalf Of Gustaf J. Barkstrom
Sent: 27 February 2004 14:35
To: PICLISTspamspam_OUTMITVMA.MIT.EDU
Subject: Re: [EE:] Release of magic smoke


Roland and all,

Okay, I don't feel too stupid now.  I was going to post
a question about separate power supplies, but then this happened.  So,
here's my question about power supply
separation:  Where is the separation?  What I mean is,
I understand using two areas of the board, but do I need
two wall-warts, two regulators, etc?  Do I have to separate them back up
to mains AC?

Yes, I chose the ULN2803A because it has the 2.7k resistors
on input; the datasheets say this is specifically for
5v TTL/CMOS connection, so I thought I was good on inputs.

Again, I'm using a 15V Zener to pin 10 (common) on the ULN2803 to
prevent back EMF.  Is that sufficient?

Thanks again,

Gustaf

{Quote hidden}

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2004\02\27@154005 by James Newton, Host

face picon face
Oooo! That is much better than "Cathy is a b**** and Annie is sweet!" which
is how I learned it. Leads to a life-long bias against Cathie's and for
Annie's! Just like Charlie brown telling his friend that the best way to
discipline a puppy was with a rolled up newspaper, and then Snoopy comments;
"Yes, but it does lead to a rather distorted view of the press"


---
James.


{Original Message removed}

2004\02\27@155455 by Anthony Toft

flavicon
face
> Oooo! That is much better than "Cathy is a b**** and Annie is
> sweet!" which is how I learned it. Leads to a life-long bias
I don't uderstand this...
I just remember that the thing _points_ in the direction it will let current
flow.

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2004\02\27@162414 by Omega Software

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face
At 15.55 27/02/2004 -0500, you wrote:
>> Oooo! That is much better than "Cathy is a b**** and Annie is
>> sweet!" which is how I learned it. Leads to a life-long bias
>
>I don't uderstand this...
>
>I just remember that the thing _points_ in the direction it will let current
>flow.

Zeners allow current to flow also in the opposite direction, at their rated
voltage.

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2004\02\27@162825 by Spehro Pefhany

picon face
At 03:55 PM 2/27/2004 -0500, you wrote:
> > Oooo! That is much better than "Cathy is a b**** and Annie is
> > sweet!" which is how I learned it. Leads to a life-long bias
>
>I don't uderstand this...
>
>I just remember that the thing _points_ in the direction it will let current
>flow.

Remember, we're talking about a zener here.. ;-)

Best regard,

Spehro Pefhany --"it's the network..."            "The Journey is the reward"
spamBeGonespeffspamBeGonespaminterlog.com             Info for manufacturers: http://www.trexon.com
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2004\02\27@205130 by Gustaf J. Barkstrom

picon face
> At 02:45 AM 2/27/2004 -0500, Spehro Pefhany wrote:
>
> It's called latch-up and results from current going through the on-chip
> protection diodes (too much current) which triggers the GIANT PARASITIC
> SCR which lives inside every PIC, right across the power supply.

Ah, I see.  Thank you for the description.

>
> >By the way, the circuit worked very well until I turned up the
> duty-cycle.
>
> It was probably marginal.

Sounds like the rest of my life. :)

> I suspect your problem is one of circuit layout. You must not allow
> motor current to flow between the ground pin on the darlington array
> and the Vss pin on the PIC.

Ah. Here's what my power and grounding looks like:

-------------------------------------------------------------
| 5v bus        (big copper pad area)                                   |
-------------*------------*-----------*---------*-----------*
                |                |               |     |               /
                |                |               | (zener) |           / motor
          [74244]      [PIC]           [ULN]--|<---*           / coil
                |                |               | \                           /
                |                |               |  \------------------*
------   ----*------------*-----------*         (to ULN outs)
|GND *-|<-*      (big copper pad area)    |
------   ------------------------------

It seems my circuit does EXACTLY what you prescribe against!
Laying it out like I did above, I can "feel" the oscillations
latching-up across the PIC.

The diode to ground is an "anti-idiot" diode to protect
against inproper polarity hookup to the power supply.  Then
again, it probably raises ground to something like 0.1v??? That's
not good if it does...

I guess I should ask the group: are beginners of my sort welcome here?

>IOW if you think of a "star" connection
> at the ground of the power supply, one point goes off to the PIC
> and one goes off to the ULNxxxx ground. You do NOT ground the PIC
> to the supply and run the connection from there to the ULNxxx (although
> the opposite would be okay). There should be a BFC (electrolytic)
> paralleled with a 0.1 ~ 1uF ceramic close to the PIC and the motor
> from ground to Vdd/5V. 1000uF 6.3V low impedance (like you
> find on a PC motherboard) works fine.

Okay, so drawing this again, I get the following???

-------------------------------------------------------------
| 5v bus        (big copper pad area)                                   |
---*---------*----*-----*-------------*---------*-----------*
  |             |      |       |                 |     |               /
  |             |      |     |           | (zener) |           / motor
[74244]    [PIC]        -     -         [ULN]--|<---*           / coil
   \____    |  -.1uF   - 1000uF          | \                           /
          |   |        |     |           |  \------------------*
------  -*---*----*-----*-------------*         (to ULN outs)
|GND *-|<-*      (big copper pad area)    |
------  -------------------------------

And, now for a new, improved design (I think):

----------------------------------    -----------------------
| Logic Vdd plane. (+5v)         |    | Motor V+ plane.     |
---*---------*----*-----*---------    *---------*-----------*
  |             |      |       |                 |     |               /
  |             |      |     |           | (zener) |           / motor
[74244]    [PIC]        -     -         [ULN]--|<---*           / coil
   \____    |  -.1uF   - 1000uF          | \______________     /
          |   |        |     |           |                \----*
---------*---*----*-----*---------        *----------------------
| Logic GND plane.               |    | Motor ground plane. |
----------------------------------    -----------------------


> BTW, you might want to put a 1K on each PIC output. Yes, there's a
> resistor inside the ULNxxx, but trust me. There's also an isolation
> junction diode to the substrate...

I didn't draw them, but I will put the 1k resistors in as well.

<gripe> Why on earth do they draw the isolation diodes with dotted
connection lines on the datasheet? </gripe>

> The zener on the catch diodes is just fine, provided it doesn't
> get too warm.

Is a catch diode a different term for "free wheeling" diode?
I saw the term "free wheeling diodes" on the datasheet, so I'm
just wondering.

I can't thank you enough!

Gustaf

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2004\02\27@205338 by Gustaf J. Barkstrom

picon face
Mike,

Thanks, I can remember that.

Gustaf

{Quote hidden}

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2004\02\27@205753 by Gustaf J. Barkstrom

picon face
Joe,

I may try that, once I separate the power supplies.  I may
also use a regular diode as opposed to the zener.  I know,
"regular diode" is probably laughable to some of you, but
that's what I'm calling it until I learn better. :) Wow, what
a learning experience this is, too.  Starting to think I should
drop the hobby and just go back to watching TV. <smirk>

Gustaf

> {Original Message removed}

2004\02\27@210622 by Gustaf J. Barkstrom

picon face
Okay, no more ASCII art from me, after seeing what Outlook did to
the tab stops.  Bloody Microsoft.  Where's my bourbon? :-)

Gustaf

> {Original Message removed}

2004\02\27@215020 by Russell McMahon

face
flavicon
face
I'll leave the others to answer the other questions, but

> I guess I should ask the group: are beginners of my sort welcome here?

Absolutely. It's appreciated if people do their homework first, as much as
they are able to (Google, PICLIST FAQ etc), but beginners are always welcome
(and also usually welcomed :-) ).

Re ASCII art
It helps if you

- use hard spaces and not tab stops
- use a fixed width (non proportional) font

Often you can redeem a scrambled picture by pasting it into another
application that treats it as it was originally treated and not as outlook /
Outlook-Express interprets it. I find that pasting ASCII art into notepad
often (but not always) makes it understandable. Not using tabs helps.



       Russell McMahon

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2004\02\28@120806 by Peter L. Peres

picon face
You likely rised the Vdd supply by the kickback pulses from the stepper
phases, through the kickback protection diodes in the ULN2003. Then the
PIC latched up and started boiling water. You have to provide a path for
the rectified kickback voltage/current to ground. In your case a simple
zener across Vdd and GND would not have been enough. You would have used
something like a dump resistor between the ULN2003 diode common and ground
(and not connect the diode common to Vdd).

Peter

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2004\02\28@133053 by Rick C.

flavicon
face
Never rely on internal diodes to do the job of external snubbing. There's no way
the substrate of the ULN device can handle the spike supression of any motor.
The internal diodes are there as a last resort, not the first line of defense.
~Rick

"Gustaf J. Barkstrom" wrote:

>   I will rely on the internal kickback protection diodes.
> Gustaf
>

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2004\02\28@135416 by Spehro Pefhany

picon face
At 01:29 PM 2/28/2004 -0500, you wrote:
>Never rely on internal diodes to do the job of external snubbing. There's
>no way
>the substrate of the ULN device can handle the spike supression of any motor.
>The internal diodes are there as a last resort, not the first line of defense.
>~Rick

Can you predict how much the peak current through the catch diodes (which
are not substrate diodes, BTW) will conduct, given the motor coil current
of, say, 170mA per phase?

Best regards,

Spehro Pefhany --"it's the network..."            "The Journey is the reward"
RemoveMEspeffEraseMEspamEraseMEinterlog.com             Info for manufacturers: http://www.trexon.com
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2004\02\28@142606 by Rick C.

flavicon
face
Yes, one can calculate the peak current. I think the overlaying issue is that lead
length between the inductive reactance of the motor coil (or a relay) and the diode
should be kept as short as possible to prevent unwanted RF emission, not just
device protection. This is why you may see diodes connected right across the motor
(or coil), and not on the circuit board. There are some dip relays that contain a
diode encapsulated within the package itself. It is far cheaper to place an
external diode in the circuit near the load than the whole ULN device should it
fail.
~Rick

Spehro Pefhany wrote:

{Quote hidden}

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2004\02\28@145026 by Scott Thomas

flavicon
face
I would definitely put resistors in series with the Darlington inputs!
Note the comment just below the schematic that Dakeng makes apologizing
for any "magic smoke" because the resistors had been omitted on earlier
schematics.

-Scott

Gustaf J. Barkstrom wrote:

{Quote hidden}

--

Thanks,

Scott Thomas

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2004\02\28@150316 by Spehro Pefhany

picon face
At 02:47 PM 2/28/2004 -0500, you wrote:
>I would definitely put resistors in series with the Darlington inputs!
>Note the comment just below the schematic that Dakeng makes apologizing
>for any "magic smoke" because the resistors had been omitted on earlier
>schematics.

The ULNxxx has internal resistors, so that comment does not apply.

The problem happens when there is a negative transient on the
ground of the ULNxxx chip relative to ground on the PIC of more than
1.2V, which means that the parasitic isolation substrate diode in
the ULNxxx will conduct, as will the protection diode in the PIC.
The current available is enough to cause the PIC to latch up (typically
in the 100mA region at room temperature, and far above the absolute
maximum 20mA rating.

Bottom line is that you can be a lot sloppier with layout if there
are resistors in there. To get 100mA through a 1K resistor you'd need
a 100V ground transient, which isn't ever going to happen with the slow-
as-molasses ULNxxx drivers.

Best regards,

Spehro Pefhany --"it's the network..."            "The Journey is the reward"
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2004\02\28@153216 by Gustaf J. Barkstrom

picon face
Yes, I did read that, but here's where I got the Darlington idea,
as opposed to using the discretes:

http://www.doc.ic.ac.uk/~ih/doc/stepper/control2/connect.html

This Ian Harris fellow didn't use the resistors, and granted his circuit
was different, vastly different; he wasn't using a PIC for his
example.  I tried to "meld" the two circuits together.  I'm learning.

I have taken your advice for my next attempt at this thing. :)

Thanks,

Gustaf

> {Original Message removed}

2004\02\28@154708 by Gustaf J. Barkstrom

picon face
I've made a handy dandy schematic for this available on my
website: http://www.excelsus.com/~remy/DualStepperSchematic.pdf

That schematic shows one half of the 4 steper circuit I am
planning to build on one PCB.  When I do, I will separate power
supplies, use a DIP 1k resistor array between the PIC and darlingtons, and
put bypassing on the logic power/gnd leads.

Thanks for all your assistance so far. :)

Gustaf
> {Original Message removed}

2004\02\28@161527 by Spehro Pefhany

picon face
At 03:49 PM 2/28/2004 -0500, you wrote:
>I've made a handy dandy schematic for this available on my
>website: http://www.excelsus.com/~remy/DualStepperSchematic.pdf
>
>That schematic shows one half of the 4 steper circuit I am
>planning to build on one PCB.  When I do, I will separate power
>supplies, use a DIP 1k resistor array between the PIC and darlingtons, and
>put bypassing on the logic power/gnd leads.
>
>Thanks for all your assistance so far. :)

Gustaf:  Connect the zener to GND rather than 5V. Other than that, it
looks good. Why the LS244?

Best regards,

Spehro Pefhany --"it's the network..."            "The Journey is the reward"
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2004\02\28@180338 by William Chops Westfield

face picon face
On Saturday, Feb 28, 2004, at 08:38 US/Pacific, Gustaf J. Barkstrom
wrote:

>
>> The interesting question is what you use to connect the two V+
>> planes, assuming you don't want two completely separate power
>> supplies...
>
> Is that possible?  Could you describe an example of how that would be
> done?
> I don't mind putting two supplies in, and I'm considering using a
> larger box
> for this project; perhaps with cooling fans and some heat sinks.
>
Of course it's POSSIBLE.  It's the logical equivalent of the noise
filter
and surge protection you find at the inputs of most switching power
supplies.
Or think of it as powering your PIC through a low-pass filter.  An
inductor
connecting the power supplies, with local capacitance on each side,
should
do pretty well, with the usual "bigger is better, except for real life"
provisos.  For some circuits, the inductance and existing bypass caps
might
be enough.  For other circuits, you need to be more agressive...

BillW

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2004\02\28@204006 by Gustaf J. Barkstrom

picon face
> At 03:49 PM 2/28/2004 -0500, Spehro Pefhany wrote:
> Gustaf:  Connect the zener to GND rather than 5V. Other than that, it
> looks good. Why the LS244?
>

I don't understand sending the zener to ground.  If I go from 5v to
the motor commons, and then to ground, that's just a zener diode between
5v and ground. On the other hand, if you mean I should put the zener
going to ground on pin 9 (gnd pin of ULN2803) then I sort of see what
you mean.  Which is it?  By the way, the wiring I have used is based
on this wiring of a ULN2003:

http://www.doc.ic.ac.uk/~ih/doc/stepper/control2/connect.html

Is the diagram on that page incorrect?

Why the LS244...
I put the LS244 in for paranoia; I don't want to blow up my computer's
printer port.  So, I thought that I would try to not sink current from
the printer port to drive the PIC.  Of course, I don't know if it's
actually doing anything.  I used the LS244 to send data into input
pins on the parallel port on another project, to buffer the lines going
into the printer port and offer some protection to the computer from my
circuit (or something connected to it).

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2004\02\28@231509 by Spehro Pefhany

picon face
At 08:44 PM 2/28/2004 -0500, you wrote:
> > At 03:49 PM 2/28/2004 -0500, Spehro Pefhany wrote:
> > Gustaf:  Connect the zener to GND rather than 5V. Other than that, it
> > looks good. Why the LS244?
> >
>
>I don't understand sending the zener to ground.  If I go from 5v to
>the motor commons, and then to ground, that's just a zener diode between
>5v and ground. On the other hand, if you mean I should put the zener
>going to ground on pin 9 (gnd pin of ULN2803) then I sort of see what
>you mean.  Which is it?

Cathode of the zener to pin 9, anode to ground (or +12 is better,
actually, provided the zener voltage isn't too high). You could just
connect pin 8 to 12V, but that would reduce the performance of the
motor.

>By the way, the wiring I have used is based
>on this wiring of a ULN2003:
>
>http://www.doc.ic.ac.uk/~ih/doc/stepper/control2/connect.html
>
>Is the diagram on that page incorrect?

No, it's fine. The problem with connecting it to +5 when the motor
is running off 12V is that you're pumping energy from the motor
inductance into the 5V bus. This could be bad, as voltage regulators
don't sink current only source it. The 5V bus will then increase
until the PIC or the LS244 dies.


>Why the LS244...
>I put the LS244 in for paranoia; I don't want to blow up my computer's
>printer port.  So, I thought that I would try to not sink current from
>the printer port to drive the PIC.  Of course, I don't know if it's
>actually doing anything.  I used the LS244 to send data into input
>pins on the parallel port on another project, to buffer the lines going
>into the printer port and offer some protection to the computer from my
>circuit (or something connected to it).

Mm. Okay. You could just use some resistors too. With 12v on the circuit
you have more reason to be concerned.

Best regards,

Spehro Pefhany --"it's the network..."            "The Journey is the reward"
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2004\02\28@232752 by Spehro Pefhany

picon face
At 11:21 PM 2/28/2004 -0500, you wrote:


>Cathode of the zener to pin 9, anode to ground (or +12 is better,
                         ^^^^^
Should read pin 10.


>actually, provided the zener voltage isn't too high). You could just
>connect pin 8 to 12V, but that would reduce the performance of the
      ^^^^^^^^
pin 10.

I think I'll quit now, not used to this much beer anymore. I'm also
working on a design with the ULN2003A driver..

Best regards,

Spehro Pefhany --"it's the network..."            "The Journey is the reward"
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2004\02\29@001648 by Gustaf J. Barkstrom

picon face
Spehro,

I am not using 12V anywhere in the circuit.  I have 5v/1A rated
stepper motors.  If you look at my schematic again
(http://www.excelsus.com/~remy/DualStepperSchematic.pdf) you will
notice that the supply is at +5V on the motors.  Actually, the entire
board, logic AND motors, is powered off the same power supply bus.
I am sorry for the confusion, as I know the folks at DAK engineering
were using 12V in their stepper circuit.

I put the zener in there because I didn't know any better, and it was
suggested on that other site.  I am thinking I'll just use a regular
diode now.  Again, everything is at +5v and gnd.

Thanks for all the assistance.  I am getting together the hardware
the steppers will move about.  Project alpha is a CNC router table
for my Dremel tool or drill press.  Project beta is a robotic tape
handler for my linux box.  My final goal is a robotic CD changer
for my home stereo.  Sure, I could put all of my CD's on hard drives,
even in PCM (i.e. wav) format, but that's boring.  It's much cooler to
have a robot that moves the discs from a largish rack and puts them
in the player, and then returns the discs to the rack when done.
Oh, women will be flocking all over me (not).

Have a good one,

Gustaf

> {Original Message removed}

2004\02\29@002724 by Ken Pergola

flavicon
face
Wow, this thread sounds like Cheech and Chong have joined the PICLIST. :)

Besides the numerous articles on the web with regard to stepper motors,
Microchip just released a bunch of app notes within the last couple of days
and weeks -- two of them on stepper motors:

AN907 Stepping Motors Fundamentals 02/23/2004
AN906 Stepper Motor Control Using the PIC16F684 02/23/2004

1) Go to Microchip's web site
2) Click on  All Application Notes
3) Sort descending (newest first)

AN910 PICmicro Device Programming: What You Always Wanted to Know (But Didn'
t Know Who to Ask) 02/25/2004
AN737 Using Digital Potentiometers to Design Low Pass Adjustable Filters
02/24/2004
TB075 Clearing the Software Write-Protect Feature on the 24LCS52 02/23/2004
AN909 SPI Communications Between Serial EEPROMs and PICmicro
Microcontrollers 02/23/2004
AN907 Stepping Motors Fundamentals 02/23/2004
AN906 Stepper Motor Control Using the PIC16F684 02/23/2004
AN905 Brushed DC Motor Fundamentals 02/23/2004
AN903 8K and 16K Microwire EEPROM Enhancements 02/11/2004
AN897 Thermistor Temperature Sensing with MCP6S2X PGA 02/11/2004


Best regards,

Ken Pergola

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2004\02\29@003347 by Ken Pergola

flavicon
face
I wrote:

> Wow, this thread sounds like Cheech and Chong have joined the PICLIST. :)

I'm referring to the *title* of this thread and not the people in this
thread, of course.

Regards,

Ken Pergola

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2004\02\29@005458 by Gustaf J. Barkstrom

picon face
Ken,

That's funny.  I hadn't thought of that!
I was referring to the addage someone wrote about electronics some time ago.
I am thinking it was a story by Don Lancaster (author of TTL Cookbook and
some other Sams Publications books) but I could be wrong.

The story goes something like the following...

Integrated circuits contain nothing but a puff of magic smoke, apparently.
They work using the magic smoke, but if the magic smoke is ever released
into the air again, the device will stop working.  For example, connect any
IC to AC mains voltage.  The magic smoke pops out, and the device
miraculously stops working.  See?  Magic Smoke I tell you!  Sometimes you
don't see the magic smoke come out, but if an IC gets really hot, sometimes
the magic smoke gets out somehow.  My goal is to keep the magic smoke inside
my IC's, so I can keep using them. ;)

The moral of the story: don't let the smoke out! ;)

The smoke floated out of my PIC, ugh.  I can't get it back in. :(
heheheh.

Gustaf
> {Original Message removed}

2004\02\29@005707 by Gustaf J. Barkstrom

picon face
Oh my!  I hadn't even thought about app notes.  I used to get
a barage of app notes from Maxim by snail mail; perhaps that turned
me off to hunting down app notes.  Anyway, thanks for the post! Woohoo.

Gustaf

> {Original Message removed}

2004\02\29@024315 by Russell McMahon

face
flavicon
face
>You would have used something like a dump resistor between the ULN2003
diode common and ground
> (and not connect the diode common to Vdd).

Good point to note - when driving a multiphase stepper from a ULN2003 the
common diode connection must *NOT* be connected directly to Vdd. This is
because the stepper acts like a transformer - when you connect one winding
between Vdd and ground the other winding which is between Vdd and an "off"
ULN2003 driver is transformer coupled to the on winding and assumes an equal
and opposite voltage to the "on" winding. As a result the voltage on the
"off" terminal rises to about twice Vdd !!!!!!!!!!!!! If you connect the
catch diode terminal to Vdd you are shorting out the off winding via its
catch diode. At the least this will drastically affect stepper operation
(and probably make it not work properly or at all) and at worst will destroy
the catch diode. Thereafter the winding will not be clamped in any way and
you will have 'trouble". In such cases the diode common needs to be
connected to something which can deal with the 2 x Vdd output or left to
float. (If left floating you have to deal with any leakage inductance spikes
some other way). Several possible energy dissipating terminations are a
resistor to Vdd, a capacitor (reduces spikes)plus discharge resistor or a
suitable zener.


       RM

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2004\02\29@072734 by Spehro Pefhany

picon face
At 08:29 PM 2/29/2004 +1300, you wrote:
> >You would have used something like a dump resistor between the ULN2003
>diode common and ground
> > (and not connect the diode common to Vdd).
>
>Good point to note - when driving a multiphase stepper from a ULN2003 the
>common diode connection must *NOT* be connected directly to Vdd.

Ah, yes, I agree, on unipolar steppers. Vdd will be bad.

{Quote hidden}

Don't forget the discharge resistor or zener as you suggest, because otherwise
the  capacitor voltage will increase, possibly beyond the 50V transistor
rating,
after many cycles.

Here's the schematic of the zener to Vdd.

                                              i
                                              --->
                       .-----------.--------------->|-----+
                       |            )|                    |
                       |            )|       /            |
                       |    +5V  o -' ----|>|-------------+
                       |            )|      /             |
                       |   i2 |     )|                    |
                       '     \ /   -'--------------->|----+
                       |          |                       |
                     |/         |/                        |
                    -|  Q1     -|   Q2                  (com)
                     |>         |>
                       |          |
                       |          |
                      ===        ===
                      GND        GND


Q1 has just turned off, and the coil current i(t) (<= steady state
coil current) is flowing through the zener, raising the collector
of Q1 to 5V+Vz. i2(t) is increasing towards steady-state coil
current.

Since the transistors are rated for 50V, a 35V or so TVS would allow
the inductive (~10mH on a small motor) current to drop faster. The
energy is ~1mJ/pulse.

Best regards,

Spehro Pefhany --"it's the network..."            "The Journey is the reward"
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2004\02\29@121609 by Scott Thomas

flavicon
face
Who is Cheech and Chong?...         just kidding ;o)

Ken Pergola wrote:

{Quote hidden}

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Thanks,

Scott Thomas

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'[EE:] Release of magic smoke'
2004\03\01@151615 by Peter L. Peres
picon face
> some other way). Several possible energy dissipating terminations are a
> resistor to Vdd,

NOT to Vdd. Feeding back power into a low current bus is guaranteed to
increase its voltage, which you do not want. The resistor must go to GND
but it can be in series with a zener to increase speed. A capacitor will
decrease spikes but will also slow down the switching so a compromise must
be made.

Peter

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