Feeding the PAK-VIIIa from a different power source?
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Posts: 46,084
I've been trying to cobble together a robotic arm. Using my bs2,
I've been able to move servos, but I'm concerned that the number of
servos I intend to run will draw too much current and blow my stamp.
I read this group avidly, and Al Williams' PAK-VIIIa seemes like the
perfect thing to run multiple servos and free up my stamp to do other
things.
I'm very new to all this, so I'm sure that there's a simple answer to
my question: How do I use a different power source to power my
servos while using the PAK-VIIIa? I'd email Al directly, but I know
he posts here, and this chip does seem like something other stampers
would enjoy seeing info about.
Using only stamp power, I have gotten the PAK to blink an led at
different rates, so I know it works.
Let me go into more detail. My setup is pretty simple. I have a bs2
w/ board of education. I'm powering that with a 9v battery. I have
an adjustable power supply that I purchased from Radio Shack. When I
set that to 4.5v, it meters closer to 5. I tried putting the +/-
from that to my servo, while attaching the pulse line from the PAK
powered by the stamp .. but the servo reacted sluggishly (not like
powering it directly by the stamp), so I'm sure something's wrong
with that. I tried powering the pak from the power supply and having
the stamp only connected to the data lines, but that doesn't seem to
work.
Any suggestions for this poor novice?
I've been able to move servos, but I'm concerned that the number of
servos I intend to run will draw too much current and blow my stamp.
I read this group avidly, and Al Williams' PAK-VIIIa seemes like the
perfect thing to run multiple servos and free up my stamp to do other
things.
I'm very new to all this, so I'm sure that there's a simple answer to
my question: How do I use a different power source to power my
servos while using the PAK-VIIIa? I'd email Al directly, but I know
he posts here, and this chip does seem like something other stampers
would enjoy seeing info about.
Using only stamp power, I have gotten the PAK to blink an led at
different rates, so I know it works.
Let me go into more detail. My setup is pretty simple. I have a bs2
w/ board of education. I'm powering that with a 9v battery. I have
an adjustable power supply that I purchased from Radio Shack. When I
set that to 4.5v, it meters closer to 5. I tried putting the +/-
from that to my servo, while attaching the pulse line from the PAK
powered by the stamp .. but the servo reacted sluggishly (not like
powering it directly by the stamp), so I'm sure something's wrong
with that. I tried powering the pak from the power supply and having
the stamp only connected to the data lines, but that doesn't seem to
work.
Any suggestions for this poor novice?
Comments
Are the two power supplies grounds tied together?
Jonathan
www.madlabs.info
Original Message
From: <robots@t...>
To: <basicstamps@yahoogroups.com>
Sent: Saturday, January 25, 2003 8:08 AM
Subject: [noparse][[/noparse]basicstamps] Feeding the PAK-VIIIa from a different power source?
> I've been trying to cobble together a robotic arm. Using my bs2,
> I've been able to move servos, but I'm concerned that the number of
> servos I intend to run will draw too much current and blow my stamp.
> I read this group avidly, and Al Williams' PAK-VIIIa seemes like the
> perfect thing to run multiple servos and free up my stamp to do other
> things.
>
> I'm very new to all this, so I'm sure that there's a simple answer to
> my question: How do I use a different power source to power my
> servos while using the PAK-VIIIa? I'd email Al directly, but I know
> he posts here, and this chip does seem like something other stampers
> would enjoy seeing info about.
>
> Using only stamp power, I have gotten the PAK to blink an led at
> different rates, so I know it works.
>
> Let me go into more detail. My setup is pretty simple. I have a bs2
> w/ board of education. I'm powering that with a 9v battery. I have
> an adjustable power supply that I purchased from Radio Shack. When I
> set that to 4.5v, it meters closer to 5. I tried putting the +/-
> from that to my servo, while attaching the pulse line from the PAK
> powered by the stamp .. but the servo reacted sluggishly (not like
> powering it directly by the stamp), so I'm sure something's wrong
> with that. I tried powering the pak from the power supply and having
> the stamp only connected to the data lines, but that doesn't seem to
> work.
>
> Any suggestions for this poor novice?
>
>
> 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/
>
>
>
>
the stamps ground? If there's a potential differnce between grounds,
could that be a bad thing? Also, one of the reasons I'm so
interested in using different power sources is, from what I've read
posted in this group, running servos and motors creates a lot of
noise on the line. Wouldn't tying the grounds together allow noise
to cross to the other electronics I'm trying to isolate (for now,
just the bs2 in this case)?
By the way Jonathan, great site you have there. I was just surfing
it on Friday. I went and bought some of the magnets you mention at
Forcefield.
Josh
--- In basicstamps@yahoogroups.com, "Jonathan Peakall"
<jpeakall@m...> wrote:
> Hi Josh,
>
> Are the two power supplies grounds tied together?
>
> Jonathan
>
> www.madlabs.info
>
>
>
Original Message
> From: <robots@t...>
> To: <basicstamps@yahoogroups.com>
> Sent: Saturday, January 25, 2003 8:08 AM
> Subject: [noparse][[/noparse]basicstamps] Feeding the PAK-VIIIa from a different power
source?
>
>
> > I've been trying to cobble together a robotic arm. Using my bs2,
> > I've been able to move servos, but I'm concerned that the number
of
> > servos I intend to run will draw too much current and blow my
stamp.
> > I read this group avidly, and Al Williams' PAK-VIIIa seemes like
the
> > perfect thing to run multiple servos and free up my stamp to do
other
> > things.
> >
> > I'm very new to all this, so I'm sure that there's a simple
answer to
> > my question: How do I use a different power source to power my
> > servos while using the PAK-VIIIa? I'd email Al directly, but I
know
> > he posts here, and this chip does seem like something other
stampers
> > would enjoy seeing info about.
> >
> > Using only stamp power, I have gotten the PAK to blink an led at
> > different rates, so I know it works.
> >
> > Let me go into more detail. My setup is pretty simple. I have a
bs2
> > w/ board of education. I'm powering that with a 9v battery. I
have
> > an adjustable power supply that I purchased from Radio Shack.
When I
> > set that to 4.5v, it meters closer to 5. I tried putting the +/-
> > from that to my servo, while attaching the pulse line from the PAK
> > powered by the stamp .. but the servo reacted sluggishly (not like
> > powering it directly by the stamp), so I'm sure something's wrong
> > with that. I tried powering the pak from the power supply and
having
> > the stamp only connected to the data lines, but that doesn't seem
to
> > work.
> >
> > Any suggestions for this poor novice?
> >
> >
> > 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/
> >
> >
> >
> >
I'm no expert, just an experimenter. But the potential difference shouldn't
be a problem, I have done a dual power supply many times with my Stamp, as
often what I want to run is well beyond the Stamp's current or voltage
capability. And I have run into problems as you describe from a loose ground
wire. As far as noise, well, if the grounds have to be connected, and the
connected devices make noise, then you have to deal with
isolating/eliminating the noise.
Try hooking up the PAK to blink the LEDs like you did off the Stamp's
supply, but use both power supplies with the common ground and see what
happens. Then if noise creates problems later, you will know that it
fundamentally works.
Glad you liked the website, motivates me to catch up and post a bunch of
stuff that has been pending!
Jonathan
www.madlabs.info
Original Message
From: <robots@t...>
To: <basicstamps@yahoogroups.com>
Sent: Saturday, January 25, 2003 8:10 PM
Subject: [noparse][[/noparse]basicstamps] Re: Feeding the PAK-VIIIa from a different power
source?
> No. So, I should just run a wire from the power supply's ground to
> the stamps ground? If there's a potential differnce between grounds,
> could that be a bad thing? Also, one of the reasons I'm so
> interested in using different power sources is, from what I've read
> posted in this group, running servos and motors creates a lot of
> noise on the line. Wouldn't tying the grounds together allow noise
> to cross to the other electronics I'm trying to isolate (for now,
> just the bs2 in this case)?
>
> By the way Jonathan, great site you have there. I was just surfing
> it on Friday. I went and bought some of the magnets you mention at
> Forcefield.
>
> Josh
>
> --- In basicstamps@yahoogroups.com, "Jonathan Peakall"
> <jpeakall@m...> wrote:
> > Hi Josh,
> >
> > Are the two power supplies grounds tied together?
> >
> > Jonathan
> >
> > www.madlabs.info
> >
> >
> >
Original Message
> > From: <robots@t...>
> > To: <basicstamps@yahoogroups.com>
> > Sent: Saturday, January 25, 2003 8:08 AM
> > Subject: [noparse][[/noparse]basicstamps] Feeding the PAK-VIIIa from a different power
> source?
> >
> >
> > > I've been trying to cobble together a robotic arm. Using my bs2,
> > > I've been able to move servos, but I'm concerned that the number
> of
> > > servos I intend to run will draw too much current and blow my
> stamp.
> > > I read this group avidly, and Al Williams' PAK-VIIIa seemes like
> the
> > > perfect thing to run multiple servos and free up my stamp to do
> other
> > > things.
> > >
> > > I'm very new to all this, so I'm sure that there's a simple
> answer to
> > > my question: How do I use a different power source to power my
> > > servos while using the PAK-VIIIa? I'd email Al directly, but I
> know
> > > he posts here, and this chip does seem like something other
> stampers
> > > would enjoy seeing info about.
> > >
> > > Using only stamp power, I have gotten the PAK to blink an led at
> > > different rates, so I know it works.
> > >
> > > Let me go into more detail. My setup is pretty simple. I have a
> bs2
> > > w/ board of education. I'm powering that with a 9v battery. I
> have
> > > an adjustable power supply that I purchased from Radio Shack.
> When I
> > > set that to 4.5v, it meters closer to 5. I tried putting the +/-
> > > from that to my servo, while attaching the pulse line from the PAK
> > > powered by the stamp .. but the servo reacted sluggishly (not like
> > > powering it directly by the stamp), so I'm sure something's wrong
> > > with that. I tried powering the pak from the power supply and
> having
> > > the stamp only connected to the data lines, but that doesn't seem
> to
> > > work.
> > >
> > > Any suggestions for this poor novice?
> > >
> > >
> > > 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/
>
>
>
>
I'm not sure that I understand why it worked though. Anyone know of
a good reference explaining this that I can go buy?
Josh
--- In basicstamps@yahoogroups.com, "Jonathan Peakall"
<jpeakall@m...> wrote:
> Josh,
>
> I'm no expert, just an experimenter. But the potential difference
shouldn't
> be a problem, I have done a dual power supply many times with my
Stamp, as
> often what I want to run is well beyond the Stamp's current or
voltage
> capability. And I have run into problems as you describe from a
loose ground
> wire. As far as noise, well, if the grounds have to be connected,
and the
> connected devices make noise, then you have to deal with
> isolating/eliminating the noise.
>
> Try hooking up the PAK to blink the LEDs like you did off the
Stamp's
> supply, but use both power supplies with the common ground and see
what
> happens. Then if noise creates problems later, you will know that it
> fundamentally works.
>
> Glad you liked the website, motivates me to catch up and post a
bunch of
> stuff that has been pending!
>
> Jonathan
>
> www.madlabs.info
>
>
>
Original Message
> From: <robots@t...>
> To: <basicstamps@yahoogroups.com>
> Sent: Saturday, January 25, 2003 8:10 PM
> Subject: [noparse][[/noparse]basicstamps] Re: Feeding the PAK-VIIIa from a different
power
> source?
>
>
> > No. So, I should just run a wire from the power supply's ground
to
> > the stamps ground? If there's a potential differnce between
grounds,
> > could that be a bad thing? Also, one of the reasons I'm so
> > interested in using different power sources is, from what I've
read
> > posted in this group, running servos and motors creates a lot of
> > noise on the line. Wouldn't tying the grounds together allow
noise
> > to cross to the other electronics I'm trying to isolate (for now,
> > just the bs2 in this case)?
> >
> > By the way Jonathan, great site you have there. I was just
surfing
> > it on Friday. I went and bought some of the magnets you mention
at
> > Forcefield.
> >
> > Josh
> >
> > --- In basicstamps@yahoogroups.com, "Jonathan Peakall"
> > <jpeakall@m...> wrote:
> > > Hi Josh,
> > >
> > > Are the two power supplies grounds tied together?
> > >
> > > Jonathan
> > >
> > > www.madlabs.info
> > >
> > >
> > >
Original Message
> > > From: <robots@t...>
> > > To: <basicstamps@yahoogroups.com>
> > > Sent: Saturday, January 25, 2003 8:08 AM
> > > Subject: [noparse][[/noparse]basicstamps] Feeding the PAK-VIIIa from a different
power
> > source?
> > >
> > >
> > > > I've been trying to cobble together a robotic arm. Using my
bs2,
> > > > I've been able to move servos, but I'm concerned that the
number
> > of
> > > > servos I intend to run will draw too much current and blow my
> > stamp.
> > > > I read this group avidly, and Al Williams' PAK-VIIIa seemes
like
> > the
> > > > perfect thing to run multiple servos and free up my stamp to
do
> > other
> > > > things.
> > > >
> > > > I'm very new to all this, so I'm sure that there's a simple
> > answer to
> > > > my question: How do I use a different power source to power
my
> > > > servos while using the PAK-VIIIa? I'd email Al directly, but
I
> > know
> > > > he posts here, and this chip does seem like something other
> > stampers
> > > > would enjoy seeing info about.
> > > >
> > > > Using only stamp power, I have gotten the PAK to blink an led
at
> > > > different rates, so I know it works.
> > > >
> > > > Let me go into more detail. My setup is pretty simple. I
have a
> > bs2
> > > > w/ board of education. I'm powering that with a 9v battery.
I
> > have
> > > > an adjustable power supply that I purchased from Radio Shack.
> > When I
> > > > set that to 4.5v, it meters closer to 5. I tried putting the
+/-
> > > > from that to my servo, while attaching the pulse line from
the PAK
> > > > powered by the stamp .. but the servo reacted sluggishly (not
like
> > > > powering it directly by the stamp), so I'm sure something's
wrong
> > > > with that. I tried powering the pak from the power supply and
> > having
> > > > the stamp only connected to the data lines, but that doesn't
seem
> > to
> > > > work.
> > > >
> > > > Any suggestions for this poor novice?
> > > >
> > > >
> > > > 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/
> >
> >
> >
> >
Remember that a circuit has to be complete for it to work. In order for the
Stamp to send a signal to the PAK, it has to have a complete circuit from
positive to negative. So basically, you were sending a signal from the Stamp
that had no place to go. Tying the grounds together made a complete circuit.
Draw it out and follow the flow, that often helps me.
Why did it work at all? Well, I'm not qualified to explain that, but it is
because of the internal circuitry of the Stamp and the PAK. Maybe someone
who knows more about hardware can jump in and explain this all better.
Anyway, at least it all works so you can have fun :-)
Jonathan
www.madlabs.info
Original Message
From: <robots@t...>
To: <basicstamps@yahoogroups.com>
Sent: Sunday, January 26, 2003 11:14 AM
Subject: [noparse][[/noparse]basicstamps] Re: Feeding the PAK-VIIIa from a different power
source?
> Connecting the grounds worked. Thanks. [noparse]:)[/noparse]
>
> I'm not sure that I understand why it worked though. Anyone know of
> a good reference explaining this that I can go buy?
>
> Josh
>
nice).
As an analogy, think of a pitcher and a catcher standing on separate
platforms that move up and down. The goal is to throw the ball between
platforms. The problem is the catcher can only catch the ball when it is
in "the strike zone" -- say from neckline to waistline. The pitcher is
good at throwing, so on the ground, they'd hit every time. But the
pitcher is blindfolded, so all he can do is throw straight ahead.
Now, as the platforms move, the pitcher winds up and throws. Most of the
time, the catcher will be above or below him. So the ball just whizzes
past and nothing happens. Every once in a while the platforms are lined
up close enough to correct that the catcher gets the ball, but not
often.
The platforms in this example are the ground potentials. Say the Stamp's
ground looks like -4V compared to the PAK's. Then when the Stamp puts
out 5V, the PAK would see 1V, which is not enough. When you tie the
grounds together you are forcing the platforms to synchronize.
Ground loops occur when you have different potentials on grounds that
are tied together. That can happen because we think wires are perfect
conductors but they are not. More importantly, they conduct differently
at different frequencies (which is very important for noise
suppression). So if a long ground wire has a resistance of .1 ohm, there
will be a definite difference between ground at one end and ground at
the other end which causes current to flow in the ground. This leads to
all sorts of problems and is something you want to avoid.
One strategy is to try to run grounds in a star pattern, so that the
losses can't build up. There are other ways to approach it, but this is
mostly a problem where grounding is poor (small wire, bad connections)
or in systems with long wires. Google on ground loops for more (Google
is a verb, right?).
Al Williams
AWC
* Special sale almost over...
http://www.al-williams.com/awce
>
Original Message
> From: Josh Holcomb <robots@t...>
> [noparse]/noparse]mailto:[url=http://forums.parallaxinc.com/group/basicstamps/post?postID=8KyIrAQNA46fyBsclaOLr4RO6KTixkwR4JyC7XSx2fhpnkjNZMIuYNdk0rARjZQnDUGpNkeAD5XKGSy7F93j_yPm]robots@t...[/url
> Sent: Sunday, January 26, 2003 1:14 PM
> To: basicstamps@yahoogroups.com
> Subject: [noparse][[/noparse]basicstamps] Re: Feeding the PAK-VIIIa from a
> different power source?
>
>
> Connecting the grounds worked. Thanks. [noparse]:)[/noparse]
>
> I'm not sure that I understand why it worked though. Anyone know of
> a good reference explaining this that I can go buy?
>
> Josh
>
>
> --- In basicstamps@yahoogroups.com, "Jonathan Peakall"
> <jpeakall@m...> wrote:
> > Josh,
> >
> > I'm no expert, just an experimenter. But the potential difference
> shouldn't
> > be a problem, I have done a dual power supply many times with my
> Stamp, as
> > often what I want to run is well beyond the Stamp's current or
> voltage
> > capability. And I have run into problems as you describe from a
> loose ground
> > wire. As far as noise, well, if the grounds have to be connected,
> and the
> > connected devices make noise, then you have to deal with
> > isolating/eliminating the noise.
> >
> > Try hooking up the PAK to blink the LEDs like you did off the
> Stamp's
> > supply, but use both power supplies with the common ground and see
> what
> > happens. Then if noise creates problems later, you will
> know that it
> > fundamentally works.
> >
> > Glad you liked the website, motivates me to catch up and post a
> bunch of
> > stuff that has been pending!
> >
> > Jonathan
> >
> > www.madlabs.info
> >
> >
> >
Original Message
> > From: <robots@t...>
> > To: <basicstamps@yahoogroups.com>
> > Sent: Saturday, January 25, 2003 8:10 PM
> > Subject: [noparse][[/noparse]basicstamps] Re: Feeding the PAK-VIIIa from a different
> power
> > source?
> >
> >
> > > No. So, I should just run a wire from the power supply's ground
> to
> > > the stamps ground? If there's a potential differnce between
> grounds,
> > > could that be a bad thing? Also, one of the reasons I'm so
> > > interested in using different power sources is, from what I've
> read
> > > posted in this group, running servos and motors creates a lot of
> > > noise on the line. Wouldn't tying the grounds together allow
> noise
> > > to cross to the other electronics I'm trying to isolate (for now,
> > > just the bs2 in this case)?
> > >
> > > By the way Jonathan, great site you have there. I was just
> surfing
> > > it on Friday. I went and bought some of the magnets you mention
> at
> > > Forcefield.
> > >
> > > Josh
> > >
> > > --- In basicstamps@yahoogroups.com, "Jonathan Peakall"
> > > <jpeakall@m...> wrote:
> > > > Hi Josh,
> > > >
> > > > Are the two power supplies grounds tied together?
> > > >
> > > > Jonathan
> > > >
> > > > www.madlabs.info
> > > >
> > > >
> > > >
Original Message
> > > > From: <robots@t...>
> > > > To: <basicstamps@yahoogroups.com>
> > > > Sent: Saturday, January 25, 2003 8:08 AM
> > > > Subject: [noparse][[/noparse]basicstamps] Feeding the PAK-VIIIa from a different
> power
> > > source?
> > > >
> > > >
> > > > > I've been trying to cobble together a robotic arm. Using my
> bs2,
> > > > > I've been able to move servos, but I'm concerned that the
> number
> > > of
> > > > > servos I intend to run will draw too much current and blow my
> > > stamp.
> > > > > I read this group avidly, and Al Williams' PAK-VIIIa seemes
> like
> > > the
> > > > > perfect thing to run multiple servos and free up my stamp to
> do
> > > other
> > > > > things.
> > > > >
> > > > > I'm very new to all this, so I'm sure that there's a simple
> > > answer to
> > > > > my question: How do I use a different power source to power
> my
> > > > > servos while using the PAK-VIIIa? I'd email Al directly, but
> I
> > > know
> > > > > he posts here, and this chip does seem like something other
> > > stampers
> > > > > would enjoy seeing info about.
> > > > >
> > > > > Using only stamp power, I have gotten the PAK to blink an led
> at
> > > > > different rates, so I know it works.
> > > > >
> > > > > Let me go into more detail. My setup is pretty simple. I
> have a
> > > bs2
> > > > > w/ board of education. I'm powering that with a 9v battery.
> I
> > > have
> > > > > an adjustable power supply that I purchased from Radio Shack.
> > > When I
> > > > > set that to 4.5v, it meters closer to 5. I tried putting the
> +/-
> > > > > from that to my servo, while attaching the pulse line from
> the PAK
> > > > > powered by the stamp .. but the servo reacted sluggishly (not
> like
> > > > > powering it directly by the stamp), so I'm sure something's
> wrong
> > > > > with that. I tried powering the pak from the power supply and
> > > having
> > > > > the stamp only connected to the data lines, but that doesn't
> seem
> > > to
> > > > > work.
> > > > >
> > > > > Any suggestions for this poor novice?
> > > > >
> > > > >
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> > > > >
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> > > > >
> > >
> > >
> > > 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/
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> > >
> > >
> > >
>
>
> 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/