Latching valve and back EMF spikes
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Posts: 46,084
Hi All,
I am wondering how I protect the Stamp from EMF spikes. I can't just put a
diode across the coil in the usual manner, as it would prevent operation in
one direction. Any ideas?
Thanks,
Jonathan
www.madlabs.info
I am wondering how I protect the Stamp from EMF spikes. I can't just put a
diode across the coil in the usual manner, as it would prevent operation in
one direction. Any ideas?
Thanks,
Jonathan
www.madlabs.info
Comments
Ok, that sounds good. I had kind of hoped to run it directly off two Stamp
pins. The current is slightly higher than the pin rating, but it for 500mS
or so, so I thought I might get away with it. Is there anyway to protect
from EMF in this situation?
Thanks very much,
Jonathan
Original Message
From: "Jim Forkin" <jjf@p...>
To: <basicstamps@yahoogroups.com>
Sent: Thursday, July 03, 2003 12:55 PM
Subject: RE: [noparse][[/noparse]basicstamps] Latching valve and back EMF spikes
> The transistors in each leg of the h-bridge have a reverse diode which
> protects it no matter which direction the current is flowing as only two
of
> the transistors are on at any given time.
>
> Jim
> http://www.geocities.com/jimforkin2003/
>
>
>
Original Message
> From: Jonathan Peakall [noparse]/noparse]mailto:[url=http://forums.parallaxinc.com/group/basicstamps/post?postID=7dXhte6G8CgqXX5yDQljq2eIaHvWd9FbAaxB9uYZP2XtI18Gczxc6H5ihNmcrK_LkJEvjvESyVJM0qatQSfWcQ]jpeakall@m...[/url
> Sent: Thursday, July 03, 2003 1:41 PM
> To: basicstamps@yahoogroups.com
> Subject: [noparse][[/noparse]basicstamps] Latching valve and back EMF spikes
>
>
> Hi All,
>
> I am wondering how I protect the Stamp from EMF spikes. I can't just put a
> diode across the coil in the usual manner, as it would prevent operation
in
> one direction. Any ideas?
>
> Thanks,
>
> Jonathan
>
> www.madlabs.info
>
>
>
>
>
>
> To UNSUBSCRIBE, just send mail to:
> basicstamps-unsubscribe@yahoogroups.com
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>
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protects it no matter which direction the current is flowing as only two of
the transistors are on at any given time.
Jim
http://www.geocities.com/jimforkin2003/
Original Message
From: Jonathan Peakall [noparse]/noparse]mailto:[url=http://forums.parallaxinc.com/group/basicstamps/post?postID=r8Tl9HuaZGhUK1Y49O_k937a__M02pCn9tu0fL9ZYpRoglmSJQK_XtBsiEZSnCIKmBMzo93Y2YkzLXg]jpeakall@m...[/url
Sent: Thursday, July 03, 2003 1:41 PM
To: basicstamps@yahoogroups.com
Subject: [noparse][[/noparse]basicstamps] Latching valve and back EMF spikes
Hi All,
I am wondering how I protect the Stamp from EMF spikes. I can't just put a
diode across the coil in the usual manner, as it would prevent operation in
one direction. Any ideas?
Thanks,
Jonathan
www.madlabs.info
To UNSUBSCRIBE, just send mail to:
basicstamps-unsubscribe@yahoogroups.com
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h-bridge gives you. Check out this web site for a schematic (and board)
which will isolate and protect the stamp and also give you an LED indication
of the status of the various pins from the stamp
Jim
http://www.geocities.com/jimforkin2003/
Original Message
From: Jonathan Peakall [noparse]/noparse]mailto:[url=http://forums.parallaxinc.com/group/basicstamps/post?postID=0-nDf0LA5yNu4mgjejL02Xi9vZ9G_Daz_gl6Xyjod4X_PMSFhY98HLWsuwHbURZhBOdNG2OGqFrJvHFIO4TDYw]jpeakall@m...[/url
Sent: Thursday, July 03, 2003 3:16 PM
To: basicstamps@yahoogroups.com
Subject: Re: [noparse][[/noparse]basicstamps] Latching valve and back EMF spikes
Jim,
Ok, that sounds good. I had kind of hoped to run it directly off two Stamp
pins. The current is slightly higher than the pin rating, but it for 500mS
or so, so I thought I might get away with it. Is there anyway to protect
from EMF in this situation?
Thanks very much,
Jonathan
Original Message
From: "Jim Forkin" <jjf@p...>
To: <basicstamps@yahoogroups.com>
Sent: Thursday, July 03, 2003 12:55 PM
Subject: RE: [noparse][[/noparse]basicstamps] Latching valve and back EMF spikes
> The transistors in each leg of the h-bridge have a reverse diode which
> protects it no matter which direction the current is flowing as only two
of
> the transistors are on at any given time.
>
> Jim
> http://www.geocities.com/jimforkin2003/
>
>
>
Original Message
> From: Jonathan Peakall [noparse]/noparse]mailto:[url=http://forums.parallaxinc.com/group/basicstamps/post?postID=0-nDf0LA5yNu4mgjejL02Xi9vZ9G_Daz_gl6Xyjod4X_PMSFhY98HLWsuwHbURZhBOdNG2OGqFrJvHFIO4TDYw]jpeakall@m...[/url
> Sent: Thursday, July 03, 2003 1:41 PM
> To: basicstamps@yahoogroups.com
> Subject: [noparse][[/noparse]basicstamps] Latching valve and back EMF spikes
>
>
> Hi All,
>
> I am wondering how I protect the Stamp from EMF spikes. I can't just put a
> diode across the coil in the usual manner, as it would prevent operation
in
> one direction. Any ideas?
>
> Thanks,
>
> Jonathan
>
> www.madlabs.info
>
>
>
>
>
>
> To UNSUBSCRIBE, just send mail to:
> basicstamps-unsubscribe@yahoogroups.com
> from the same email address that you subscribed. Text in the Subject and
> Body of the message will be ignored.
>
>
> Your use of Yahoo! Groups is subject to http://docs.yahoo.com/info/terms/
>
>
>
> To UNSUBSCRIBE, just send mail to:
> basicstamps-unsubscribe@yahoogroups.com
> from the same email address that you subscribed. Text in the Subject and
Body of the message will be ignored.
>
>
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>
>
>
>
>
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would block the voltage forward (up to 6 volts)
so it would drive the coil, but then when the
coil shuts off, would limit the voltage
rise to 6 volts as the current collapses.
Just a thought -- perhaps an inept one, though.
--- In basicstamps@yahoogroups.com, "Jonathan Peakall"
<jpeakall@m...> wrote:
> Hi All,
>
> I am wondering how I protect the Stamp from EMF spikes. I can't
just put a
> diode across the coil in the usual manner, as it would prevent
operation in
> one direction. Any ideas?
>
> Thanks,
>
> Jonathan
>
> www.madlabs.info
You have nerves of steel running Stamp I/O pins over the rated max -- even
for 1/2 second ;-) But I don't think it would work, and here's why...
When you draw anywhere near the max rated current from a Stamp/PICmicro pin,
there is a significant voltage drop across the internal driver transistor.
Let's say you are sourcing 20 or 25 mA from the I/O pin. You won't get
anywhere near 5.0 volts out. I haven't done this with the PIC 16C57 used in
the Stamp, but I have with some of the current PICmicros. My notes are
around here somewhere, but as I recall the voltage was getting down near 2.5
as the max rated current was reached. You would also have a similar
situation on the Stamp I/O pin used on the ground side, but not quite as
extreme. Bottom line: you wouldn't have anywhere near the 5 volts needed
for your solenoid if you attempt to drive it directly from the I/O pins.
You could build a small H-bridge from 6 dirt-cheap transistors if you
wanted. I think there was a link about this in one of the replies you got
last week. Here is another (schematic of the Furby) -- note the two
combinations of three transistors used to drive the motor. You could use
2N3904/2N3906, or any other cheap switching transistors.
http://www.hackfurby.com/schematic.html
Randy
www.glitchbuster.com
Original Message
From: "Jonathan Peakall" <jpeakall@m...>
To: <basicstamps@yahoogroups.com>
Sent: Thursday, July 03, 2003 12:15 PM
Subject: Re: [noparse][[/noparse]basicstamps] Latching valve and back EMF spikes
> Jim,
>
> Ok, that sounds good. I had kind of hoped to run it directly off two Stamp
> pins. The current is slightly higher than the pin rating, but it for 500mS
> or so, so I thought I might get away with it. Is there anyway to protect
> from EMF in this situation?
>
> Thanks very much,
>
> Jonathan
>
>
Original Message
> From: "Jim Forkin" <jjf@p...>
> To: <basicstamps@yahoogroups.com>
> Sent: Thursday, July 03, 2003 12:55 PM
> Subject: RE: [noparse][[/noparse]basicstamps] Latching valve and back EMF spikes
>
>
> > The transistors in each leg of the h-bridge have a reverse diode which
> > protects it no matter which direction the current is flowing as only two
> of
> > the transistors are on at any given time.
> >
> > Jim
> > http://www.geocities.com/jimforkin2003/
> >
> >
> >
Original Message
> > From: Jonathan Peakall [noparse]/noparse]mailto:[url=http://forums.parallaxinc.com/group/basicstamps/post?postID=TiWvk97kWYkv3fQrwlMTfF4ig_vjQzZC6dC-nyCD6Ex_Hm03LTaaEptHT4gimlw2WaCglVY6k4q-GNb1piU]jpeakall@m...[/url
> > Sent: Thursday, July 03, 2003 1:41 PM
> > To: basicstamps@yahoogroups.com
> > Subject: [noparse][[/noparse]basicstamps] Latching valve and back EMF spikes
> >
> >
> > Hi All,
> >
> > I am wondering how I protect the Stamp from EMF spikes. I can't just put
a
> > diode across the coil in the usual manner, as it would prevent operation
> in
> > one direction. Any ideas?
> >
> > Thanks,
> >
> > Jonathan
> >
> > www.madlabs.info
> >
> >
> >
> >
> >
> >
> > To UNSUBSCRIBE, just send mail to:
> > basicstamps-unsubscribe@yahoogroups.com
> > from the same email address that you subscribed. Text in the Subject
and
> > Body of the message will be ignored.
> >
> >
> > Your use of Yahoo! Groups is subject to
http://docs.yahoo.com/info/terms/
> >
> >
> >
> > To UNSUBSCRIBE, just send mail to:
> > basicstamps-unsubscribe@yahoogroups.com
> > from the same email address that you subscribed. Text in the Subject
and
> Body of the message will be ignored.
> >
> >
> > Your use of Yahoo! Groups is subject to
http://docs.yahoo.com/info/terms/
> >
> >
> >
> >
> >
>
>
> To UNSUBSCRIBE, just send mail to:
> basicstamps-unsubscribe@yahoogroups.com
> from the same email address that you subscribed. Text in the Subject and
Body of the message will be ignored.
>
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>
>