Building an H Bridge
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I need to get my new PIC chips to control some motors. I have asked a
question similar to this before, but last night when I was playing around
with my BSII and the PIC, trying to get them to communicate with each other
serially, I though about my robot's potential drive system. I had been
envisioning a transistor accepting input from a dedicated drive control PIC
and connecting vss to the motor. When I output a PWM from the PIC it should
cause the transistor to switch on and off rapidly (it is going to be a
high-speed switching transistor), making the motor go at variable speeds.
Does that sound workable so far? It does to me... Then I remembered that I
want to be able to make it go in reverse too. In the back of my mind I had
been thinking that I would only need another transistor on the +6VDC line to
the motor. Even minimal scrutiny of that idea will reveal that it has some
problems... such as not reversing the polarity of the input current (I don't
know if that is the right term, but it makes sense). So what I need to do
is build or buy an H bridge. I found a couple in Digi-Key's magazine, but I
am afraid that they won't offer a high enough switching speed to work with a
PWM. So I want to build my own. I can't seem to quite get the curcuit
diagrammed. I think I need 3 transistors and some diodes to control the
direction of the electricity. Is it true that a transistor will only
operate if the electricity is going in a certain direction? If it acts like
a diode, that would simplify my curcuit a lot. I am using NPN transistors,
btw. Not that I know the difference between NPN and PNP or anything...
everyone else uses them [noparse]:)[/noparse] If you feel like giving me a little help with
this, please do!
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Sign up at http://www.mail.com/?sr=signup
question similar to this before, but last night when I was playing around
with my BSII and the PIC, trying to get them to communicate with each other
serially, I though about my robot's potential drive system. I had been
envisioning a transistor accepting input from a dedicated drive control PIC
and connecting vss to the motor. When I output a PWM from the PIC it should
cause the transistor to switch on and off rapidly (it is going to be a
high-speed switching transistor), making the motor go at variable speeds.
Does that sound workable so far? It does to me... Then I remembered that I
want to be able to make it go in reverse too. In the back of my mind I had
been thinking that I would only need another transistor on the +6VDC line to
the motor. Even minimal scrutiny of that idea will reveal that it has some
problems... such as not reversing the polarity of the input current (I don't
know if that is the right term, but it makes sense). So what I need to do
is build or buy an H bridge. I found a couple in Digi-Key's magazine, but I
am afraid that they won't offer a high enough switching speed to work with a
PWM. So I want to build my own. I can't seem to quite get the curcuit
diagrammed. I think I need 3 transistors and some diodes to control the
direction of the electricity. Is it true that a transistor will only
operate if the electricity is going in a certain direction? If it acts like
a diode, that would simplify my curcuit a lot. I am using NPN transistors,
btw. Not that I know the difference between NPN and PNP or anything...
everyone else uses them [noparse]:)[/noparse] If you feel like giving me a little help with
this, please do!
______________________________________________
FREE Personalized Email at Mail.com
Sign up at http://www.mail.com/?sr=signup
Comments
Bob Blick's H-bridge http://www.bobblick.com/bob/projects/hbridge/index.html
or
a group of pages titles 'Using MOSFETs Page' that include 4 different
H-bridges starting at http://www.cadvision.com/blanchas/hexfet/.
Hope this helps
Daniel McGlothin
Original Message
From: Yanroy [noparse]/noparse]mailto:[url=http://forums.parallaxinc.com/group/basicstamps/post?postID=s675h23gBFpn_4qWyCfQPJqbu9R5Z8Ub5E2K2SPu51-7Mt7AHruuzAyJKXn-SCekzYOg_Q]yanroy@u...[/url
Sent: Friday, February 02, 2001 8:40 AM
To: basicstamps@yahoogroups.com
Subject: [noparse][[/noparse]basicstamps] Building an H Bridge
I need to get my new PIC chips to control some motors. I have asked a
question similar to this before, but last night when I was playing around
with my BSII and the PIC, trying to get them to communicate with each other
serially, I though about my robot's potential drive system. I had been
envisioning a transistor accepting input from a dedicated drive control PIC
and connecting vss to the motor. When I output a PWM from the PIC it should
cause the transistor to switch on and off rapidly (it is going to be a
high-speed switching transistor), making the motor go at variable speeds.
Does that sound workable so far? It does to me... Then I remembered that I
want to be able to make it go in reverse too. In the back of my mind I had
been thinking that I would only need another transistor on the +6VDC line to
the motor. Even minimal scrutiny of that idea will reveal that it has some
problems... such as not reversing the polarity of the input current (I don't
know if that is the right term, but it makes sense). So what I need to do
is build or buy an H bridge. I found a couple in Digi-Key's magazine, but I
am afraid that they won't offer a high enough switching speed to work with a
PWM. So I want to build my own. I can't seem to quite get the curcuit
diagrammed. I think I need 3 transistors and some diodes to control the
direction of the electricity. Is it true that a transistor will only
operate if the electricity is going in a certain direction? If it acts like
a diode, that would simplify my curcuit a lot. I am using NPN transistors,
btw. Not that I know the difference between NPN and PNP or anything...
everyone else uses them [noparse]:)[/noparse] If you feel like giving me a little help with
this, please do!
______________________________________________
FREE Personalized Email at Mail.com
Sign up at http://www.mail.com/?sr=signup
with success. You might try using a low pass filter on the BS2's
output, this will generate a level of DC voltage instead of pulses
(most small DC motors run better on pure DC). Feed this voltage into
an opamp and on to your power transistor. Use a DPDT relay between
the motor and transistor to control motor direction via the BS2.
Remember, DC motors don't like to be reversed at high speed or under
load. It shortens the life of the magnets. Dave Thompson
--- In basicstamps@y..., Yanroy <yanroy@u...> wrote:
> I need to get my new PIC chips to control some motors. I have
asked a
> question similar to this before, but last night when I was playing
around
> with my BSII and the PIC, trying to get them to communicate with
each other
> serially, I though about my robot's potential drive system. I had
been
> envisioning a transistor accepting input from a dedicated drive
control PIC
> and connecting vss to the motor. When I output a PWM from the PIC
it should
> cause the transistor to switch on and off rapidly (it is going to
be a
> high-speed switching transistor), making the motor go at variable
speeds.
> Does that sound workable so far? It does to me... Then I
remembered that I
> want to be able to make it go in reverse too. In the back of my
mind I had
> been thinking that I would only need another transistor on the
+6VDC line to
> the motor. Even minimal scrutiny of that idea will reveal that it
has some
> problems... such as not reversing the polarity of the input current
(I don't
> know if that is the right term, but it makes sense). So what I
need to do
> is build or buy an H bridge. I found a couple in Digi-Key's
magazine, but I
> am afraid that they won't offer a high enough switching speed to
work with a
> PWM. So I want to build my own. I can't seem to quite get the
curcuit
> diagrammed. I think I need 3 transistors and some diodes to
control the
> direction of the electricity. Is it true that a transistor will
only
> operate if the electricity is going in a certain direction? If it
acts like
> a diode, that would simplify my curcuit a lot. I am using NPN
transistors,
> btw. Not that I know the difference between NPN and PNP or
anything...
> everyone else uses them [noparse]:)[/noparse] If you feel like giving me a little
help with
> this, please do!
>
>
> ______________________________________________
> FREE Personalized Email at Mail.com
> Sign up at http://www.mail.com/?sr=signup
http://www.cs.uwa.edu.au/~mafm/robot/blanch-h-bridge.html
--- In basicstamps@y..., Yanroy <yanroy@u...> wrote:
> I need to get my new PIC chips to control some motors. I have
asked a
> question similar to this before, but last night when I was playing
around
> with my BSII and the PIC, trying to get them to communicate with
each other
> serially, I though about my robot's potential drive system. I had
been
> envisioning a transistor accepting input from a dedicated drive
control PIC
> and connecting vss to the motor. When I output a PWM from the PIC
it should
> cause the transistor to switch on and off rapidly (it is going to
be a
> high-speed switching transistor), making the motor go at variable
speeds.
> Does that sound workable so far? It does to me... Then I
remembered that I
> want to be able to make it go in reverse too. In the back of my
mind I had
> been thinking that I would only need another transistor on the
+6VDC line to
> the motor. Even minimal scrutiny of that idea will reveal that it
has some
> problems... such as not reversing the polarity of the input current
(I don't
> know if that is the right term, but it makes sense). So what I
need to do
> is build or buy an H bridge. I found a couple in Digi-Key's
magazine, but I
> am afraid that they won't offer a high enough switching speed to
work with a
> PWM. So I want to build my own. I can't seem to quite get the
curcuit
> diagrammed. I think I need 3 transistors and some diodes to
control the
> direction of the electricity. Is it true that a transistor will
only
> operate if the electricity is going in a certain direction? If it
acts like
> a diode, that would simplify my curcuit a lot. I am using NPN
transistors,
> btw. Not that I know the difference between NPN and PNP or
anything...
> everyone else uses them [noparse]:)[/noparse] If you feel like giving me a little
help with
> this, please do!
>
>
> ______________________________________________
> FREE Personalized Email at Mail.com
> Sign up at http://www.mail.com/?sr=signup