PWM
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Posts: 46,084
I need help to a project where I need to have a stamp capable to generate 3
square wave frequencies:
20Hz, 150 Hz and 5 KHz with duty cycle 50% .I did the inputs part but I can
not have the frequencies
at 50% duty cycle. I have the right pulse ON but the OFF period between the
pulses is very short, which make like 90% duty cycle and not 50%.
Help please
Thank you
Ion
square wave frequencies:
20Hz, 150 Hz and 5 KHz with duty cycle 50% .I did the inputs part but I can
not have the frequencies
at 50% duty cycle. I have the right pulse ON but the OFF period between the
pulses is very short, which make like 90% duty cycle and not 50%.
Help please
Thank you
Ion
Comments
I have BS2p. Tryyed an alternate code to make a dc gearhead go first one
way for 120 degrees, pause, then return to its spot, pause, ectc....
Willlater incorpoarate sensor code..... but I digress
I am using an h brdige from HVW technologies.............
(L298, i believe)
any who......i wrote a code that was non, PWM, and I don't think it worked,
So I have pin 0 as grnd
pin 1 as forward
and pin 2 as backward..
how in the hellena do i write this code????
johnny be stupid
why with an hbridge motor contoller,
if i use the following instruction PWM 0,16,25 it slow down my motor,
and if i had this intruction PWM 2,16,25 then boths motors go back
to high speed, i'm using an BS2
surely there's something that i dont understand about PWM
thanks
John
johneck790@s... writes:
> hi,
> why with an hbridge motor contoller,
> if i use the following instruction PWM 0,16,25 it slow down my motor,
> and if i had this intruction PWM 2,16,25 then boths motors go back
> to high speed, i'm using an BS2
> surely there's something that i dont understand about PWM
>
> thanks
>
> John
I did not see your original post but.....
An H bridge is a convenient way to reverse the motor direction (polarity of
voltage applied to motor)
I don't know if you are driving the motor directly with the stamp or
not....but the H bridge will also use less "drive" current from the stamp.
The H bridge is not needed if the motor direction will always be the same.
H bridge or not, it is always a good idea to drive the motor with a MOSFET of
some kind to reduce the current needed by the stamp to drive the motor...
[noparse][[/noparse]Non-text portions of this message have been removed]
my hbridge works fine, the problem is how to program the BS2 to make it work
motor by motor PWM works, it's when i try both motors at the same time that
doesnt!
rightfwd con 0
leftfwd con 2
rightbck =0
leftbck =0
pwm rightfwd, 16,25
pwm leftfwd, 16,25
what's wrong with this program?
John
Original Message
From: basicstamps@yahoogroups.com
Date: June 23, 2003 11:43:23 AM
To: basicstamps@yahoogroups.com
Subject: Re: [noparse][[/noparse]basicstamps] PWM
In a message dated 6/23/2003 6:36:16 AM Pacific Daylight Time,
johneck790@s... writes:
> hi,
> why with an hbridge motor contoller,
> if i use the following instruction PWM 0,16,25 it slow down my motor,
> and if i had this intruction PWM 2,16,25 then boths motors go back
> to high speed, i'm using an BS2
> surely there's something that i dont understand about PWM
>
> thanks
>
> John
I did not see your original post but.....
An H bridge is a convenient way to reverse the motor direction (polarity of
voltage applied to motor)
I don't know if you are driving the motor directly with the stamp or
not....but the H bridge will also use less "drive" current from the stamp.
The H bridge is not needed if the motor direction will always be the same.
H bridge or not, it is always a good idea to drive the motor with a MOSFET
of
some kind to reduce the current needed by the stamp to drive the motor...
[noparse][[/noparse]Non-text portions of this message have been removed]
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.
[noparse][[/noparse]Non-text portions of this message have been removed]
generate an analog voltage through an RC filter. We will be releasing an
accessory module called the PWMPAL that mounts under the Stamp and will let you
create (background) PWM streams (up to four) that can run motors.
-- Jon Williams
-- Parallax
In a message dated 6/23/2003 2:15:52 PM Central Standard Time,
johneck790@s... writes:
> Thanks,
>
> my hbridge works fine, the problem is how to program the BS2 to make it work
>
> motor by motor PWM works, it's when i try both motors at the same time that
> doesnt!
>
> rightfwd con 0
> leftfwd con 2
>
> rightbck =0
> leftbck =0
> pwm rightfwd, 16,25
> pwm leftfwd, 16,25
>
> what's wrong with this program?
>
> John
>
[noparse][[/noparse]Non-text portions of this message have been removed]
specific about what kind of bridge circuit you are using?
Keep in mind that the Stamp's PWM command only generates PWM for a fixed
duration. If you want up to 8 continuous PWM outputs, have a look at
http://www.al-williams.com/pak5.htm
Al Williams
AWC
* Floating point A/D
http://www.al-williams.com/awce/pak9.htm
>
Original Message
> From: John Courtney [noparse]/noparse]mailto:[url=http://forums.parallaxinc.com/group/basicstamps/post?postID=g_mwCyt3-tGim60KJit6StiN0vMprn8srmw2eMhIs2Al3xC4olE2XUCgd2IuTHibVuYWWqVlh0_hsosMtC-vMANm]johneck790@s...[/url
> Sent: Monday, June 23, 2003 2:14 PM
> To: basicstamps@yahoogroups.com
> Subject: Re: [noparse][[/noparse]basicstamps] PWM
>
>
> Thanks,
>
>
>
> my hbridge works fine, the problem is how to program the BS2
> to make it work
>
>
> motor by motor PWM works, it's when i try both motors at the
> same time that doesnt!
>
>
>
> rightfwd con 0
>
> leftfwd con 2
>
>
>
> rightbck =0
>
> leftbck =0
>
> pwm rightfwd, 16,25
>
> pwm leftfwd, 16,25
>
>
>
> what's wrong with this program?
>
>
>
> John
>
>
>
>
Original Message
>
>
>
> From: basicstamps@yahoogroups.com
>
> Date: June 23, 2003 11:43:23 AM
>
> To: basicstamps@yahoogroups.com
>
> Subject: Re: [noparse][[/noparse]basicstamps] PWM
>
>
>
> In a message dated 6/23/2003 6:36:16 AM Pacific Daylight Time,
>
> johneck790@s... writes:
>
>
>
> > hi,
>
> > why with an hbridge motor contoller,
>
> > if i use the following instruction PWM 0,16,25 it slow down
> my motor,
>
> > and if i had this intruction PWM 2,16,25 then boths motors go back
>
> > to high speed, i'm using an BS2
>
> > surely there's something that i dont understand about PWM
>
> >
>
> > thanks
>
> >
>
> > John
>
>
>
> I did not see your original post but.....
>
>
>
> An H bridge is a convenient way to reverse the motor
> direction (polarity of
>
> voltage applied to motor)
>
> I don't know if you are driving the motor directly with the stamp or
>
> not....but the H bridge will also use less "drive" current
> from the stamp.
>
>
>
> The H bridge is not needed if the motor direction will always
> be the same.
>
>
>
> H bridge or not, it is always a good idea to drive the motor
> with a MOSFET of
>
> some kind to reduce the current needed by the stamp to drive
> the motor...
>
>
>
>
>
> [noparse][[/noparse]Non-text portions of this message have been removed]
>
>
>
>
>
> 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/
.
[noparse][[/noparse]Non-text portions of this message have been removed]
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Soon is right now. The PWMPAL is in stock and ready for shipment. The
product ships with printed documentation that will help you get familiar
with this new device. It requires a BASIC Stamp of the 24 pin variety
(sold separately).
For more information please visit the PWMPAL product page at this link -
http://www.parallax.com/detail.asp?product_id=28020
Sincerely,
Erik Wood
ewood@p...
Parallax, Inc.
599 Menlo Dr., Suite #100
Rocklin, CA 95765
(916) 624-8003 Fax
(888) 512-1024 Sales
http://www.parallax.com
Check out our BASIC Stamp Courses!
http://www.parallax.com/html_pages/edu/courses/registration.asp
Original Message
From: Jon Williams (AOL)
Sent: Monday, June 23, 2003 12:27 PM
To: basicstamps@yahoogroups.com
Subject: Re: [noparse][[/noparse]basicstamps] PWM
The Stamp's PWM command is NOT designed for motor control; it is
designed to
generate an analog voltage through an RC filter. We will be releasing
an
accessory module called the PWMPAL that mounts under the Stamp and will
let you
create (background) PWM streams (up to four) that can run motors.
-- Jon Williams
-- Parallax
In a message dated 6/23/2003 2:15:52 PM Central Standard Time,
johneck790@s... writes:
> Thanks,
>
> my hbridge works fine, the problem is how to program the BS2 to make
> it work
>
> motor by motor PWM works, it's when i try both motors at the same time
> that doesnt!
>
> rightfwd con 0
> leftfwd con 2
>
> rightbck =0
> leftbck =0
> pwm rightfwd, 16,25
> pwm leftfwd, 16,25
>
> what's wrong with this program?
>
> John
>
[noparse][[/noparse]Non-text portions of this message have been removed]
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basicstamps-unsubscribe@yahoogroups.com
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This message has been scanned by WebShield. Please report SPAM to
abuse@p....
Thx.
designed to be filtered in order to create an analog output. It is
different from PWM outputs that are used to drive DC motors.
-- Jon Williams
-- Applications Engineer, Parallax
-- Dallas Office
Original Message
From: alexetouioui3 [noparse]/noparse]mailto:[url=http://forums.parallaxinc.com/group/basicstamps/post?postID=ID4JQ6toPzVal09nbFniiIPnoRluWFiC6h3UoctoiC6pNFLf2Vs8CXJShY-UmUPWJQCqTeVjazUiY-noX-H01G_d]alexetouioui@h...[/url
Sent: Tuesday, June 01, 2004 4:45 AM
To: basicstamps@yahoogroups.com
Subject: [noparse][[/noparse]basicstamps] PWM
Who can explain me how the PWM command works?
Thx.
>
>Thx.
There is an extra explanation at <http://www.emesys.com/BS2PWM.htm>.
> >Who can explain me how the PWM command works?
> >
> >Thx.
>
> There is an extra explanation at < http://www.emesys.com/BS2PWM.htm >.
Good write up. The old manual under Basic Stamp 1 App notes, says
that using the circuit, they got up to about 15 minutes of an output
for a single burst of PWM. Your notes say seconds.
Any idea why the difference ?
does changing the pin state after a burst have any effect on the
duration of the sigal ?
Dave
opamp buffer as shown on Tracy's web site.
-- Jon Williams
-- Applications Engineer, Parallax
-- Dallas Office
Original Message
From: Dave Mucha [noparse]/noparse]mailto:[url=http://forums.parallaxinc.com/group/basicstamps/post?postID=F6mMxJGJTjZmEK9YLq491E8fLbVoyaAsPZR9tQ1UT0wGvfHYuwUdd099QmD3363bsX3taCalCW3uvyV3]davemucha@j...[/url
Sent: Tuesday, June 01, 2004 11:21 AM
To: basicstamps@yahoogroups.com
Subject: [noparse][[/noparse]basicstamps] Re: PWM
--- In basicstamps@yahoogroups.com, Tracy Allen <tracy@e...> wrote:
> >Who can explain me how the PWM command works?
> >
> >Thx.
>
> There is an extra explanation at < http://www.emesys.com/BS2PWM.htm >.
Good write up. The old manual under Basic Stamp 1 App notes, says
that using the circuit, they got up to about 15 minutes of an output
for a single burst of PWM. Your notes say seconds.
Any idea why the difference ?
does changing the pin state after a burst have any effect on the
duration of the sigal ?
Dave
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abuse@p....
With a good CMOS input op-amp, the hold time can indeed be minutes.
There is a leakage current which depends on the op-amp, the BASIC
Stamp input, the capacitor and also on how clean and dry your circuit
board is.
The falloff in voltage with time is usually called "droop" and it
might be millivolts per second. If it only needs to hold within 0.1
volt, the acceptable time will be much longer than if it needs to
hold within 1 millivolt. You can easily measure it with a voltmeter
on the output of the op amp.
Pay attention to the business mentioned in my web writeup, about
interaction (clock feedthrough) between adjacent channels. PWM to
p0 and then PWM to p1, the value on p0 will change under some
conditions. The web page write-up shows how to get around that by
using a snubber capacitor.
Also you have to be aware that a PWM value that holds a voltage near
the Stamp input switching threshold will cause the Stamp to draw
excess current. That is in the nature of the CMOS digital input,
which is not really designed to be used in the linear mode near that
threshold. (It is great! that it works though). The excess current
will be about 1.5 milliamps per pin held near 1.5 volts.
You can see this spike of current on a millamp-meter monitoring the
Stamp current as it sweeps filtered PWM through the threshold.
Any command that addresses the same 8-bit port on which PWM is
operating, may cause the PWM value to shift slightly. For example,
if you have PWM output on p0 and p1, and you have a shiftout command
on p3 to p5 on the same 8-bit port, that will cause the PWM values
held on p0 and p1 to shift slightly. There is the clock feedthrough
effect mentioned above that can be snubbed, but also there is another
effect when p0 or p1 are held near the switching threshold. It is as
if the pins briefly become outputs during the read-modify-write cycle
on the port. I can not be too clear about that, because I don't
understand exactly what is going on. But it is one of those little
things that might surprise you if you are not expecting any
interaction at all. Those effects can make the PWM'd value to droop
or increase, depending...
-- best regards,
Tracy
>--- In basicstamps@yahoogroups.com, Tracy Allen <tracy@e...> wrote:
>> >Who can explain me how the PWM command works?
>> >
>> >Thx.
>>
>> There is an extra explanation at < http://www.emesys.com/BS2PWM.htm >.
>
>
>Good write up. The old manual under Basic Stamp 1 App notes, says
>that using the circuit, they got up to about 15 minutes of an output
>for a single burst of PWM. Your notes say seconds.
>
>Any idea why the difference ?
>
>does changing the pin state after a burst have any effect on the
>duration of the sigal ?
>
>Dave
>