Mosfet and Board of Education
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Need some help with a Mosfet.
I'm preparing to enter a fire fighting contest using
my Board of Education. The Bot rolls navigates the
rooms just fine, but I don't have an extinguisher.
My plan is to add a motor and propeller to put out the
fire. My bot is powered by a 9.7 volt Makita battery.
It is this power though a Radio Shack Mosfet that I
plan to use for the motor.
I've wired the mosfet with Vin to the Drain and Vss to
the Source of the mosfet. The gate is triggered by
pin 11. The bot has two futaba servos triggered by
pins 12 and 13.
Here is my problem. When I activate the mosfet to
power the propeller, both servos spin too. My
program is simple.
start:
Low 11
pause 2000
high 11
pause 2000
goto start
I'm stumped. Any help will be appreciated.
Dave Cousins.
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I'm preparing to enter a fire fighting contest using
my Board of Education. The Bot rolls navigates the
rooms just fine, but I don't have an extinguisher.
My plan is to add a motor and propeller to put out the
fire. My bot is powered by a 9.7 volt Makita battery.
It is this power though a Radio Shack Mosfet that I
plan to use for the motor.
I've wired the mosfet with Vin to the Drain and Vss to
the Source of the mosfet. The gate is triggered by
pin 11. The bot has two futaba servos triggered by
pins 12 and 13.
Here is my problem. When I activate the mosfet to
power the propeller, both servos spin too. My
program is simple.
start:
Low 11
pause 2000
high 11
pause 2000
goto start
I'm stumped. Any help will be appreciated.
Dave Cousins.
__________________________________________________
Do You Yahoo!?
Get email at your own domain with Yahoo! Mail.
http://personal.mail.yahoo.com/
Comments
dropping too low, the Basic Stamp will reset itself. Perhaps when the motor
runs, it is drawing too much current, and that is causing the brownout. Do
you have an independent battery for the BS2?
Paul
> Here is my problem. When I activate the mosfet to
> power the propeller, both servos spin too. My
> program is simple.
first post because I didn't think it was important.
Keep in mind that the BOE powers the servos using a direct feed of
the 9.7 volt Makita battery. This voltage powers the servos nicely,
so, I thought that it could handle the little 12 volt motor. BTW, the
motor doesn't currently have a propeller, so it's running free. Is
that a concern with a Brownout?
--- In basicstamps@y..., Paul Verhage <pverhage@s...> wrote:
> Is the Basic Stamp experiencing a brownout? If the voltage supply
is
> dropping too low, the Basic Stamp will reset itself. Perhaps when
the motor
> runs, it is drawing too much current, and that is causing the
brownout. Do
> you have an independent battery for the BS2?
>
> Paul
>
> > Here is my problem. When I activate the mosfet to
> > power the propeller, both servos spin too. My
> > program is simple.
Dave
> the 9.7 volt Makita battery. This voltage powers the servos nicely,
> so, I thought that it could handle the little 12 volt motor. BTW, the
> motor doesn't currently have a propeller, so it's running free. Is
> that a concern with a Brownout?
If it's a brownout, it doesn't hurt the BS2. But it will continually
restart the program. Use a seperate battery for the BS2, or add a 3300uF
cap between powert and ground, close to the BS2, to act as a temporary
battery. Whenever the motor starts up, it is drawing too much current, the
battery can't keep the voltage up.
Paul
both systems? Sorry for the very basic questions. I'm a Civil
Engineer. Also, do you think my other problem will be solved?
> Here is my problem. When I activate the mosfet to
> power the propeller motor, both servos and the motor spin.
Thanks,
Dave
--- In basicstamps@y..., Paul Verhage <pverhage@s...> wrote:
> If it's a brownout, it doesn't hurt the BS2. But it will
continually
> restart the program. Use a seperate battery for the BS2, or add a
3300uF
> cap between powert and ground, close to the BS2, to act as a
temporary
> battery. Whenever the motor starts up, it is drawing too much
current, the
> battery can't keep the voltage up.
>
> Paul
> both systems? Sorry for the very basic questions. I'm a Civil
> Engineer. Also, do you think my other problem will be solved?
Yep, connect the grounds. Don't worry about basic questions, I still ask
them, myself.
If the problem is brownout, then this should take care of the resets.
Paul
> > power the propeller motor, both servos and the motor spin.
What I suspect is happening is that the prop motor draws down the voltage so
much that the BS2 resets. Once it resets, the signal to the MOSFET goes
low, turning it off. The prop motor now shuts off, letting the voltage come
back up. Now the BS2 can restart. The BS2 begins by executing the first
instruction, which I imagine is the commands to operate the servos. But
once the propellor motor starts up, it will reset the BS2 and begin the
process over again.
You could do this experiment. Put a pause (say 5 sec) before operating the
prop motor. Now the BOE-BOT will operate properly for 5 seconds longer
before browning out.
If you try to operate the prop motor and servos early in the code, then the
BOE-BOT will continually spin both, but never accomplish anything because it
is reseting itself.
Paul
> > > Here is my problem. When I activate the mosfet to
> > > power the propeller motor, both servos and the motor spin.
>
> You could do this experiment. Put a pause (say 5 sec) before
operating the
> prop motor. Now the BOE-BOT will operate properly for 5 seconds
longer
> before browning out.
> If you try to operate the prop motor and servos early in the code,
then the
> BOE-BOT will continually spin both, but never accomplish anything
because it
> is reseting itself.
>
> Paul
Paul,
Some kind of magic is happening. My code is very basic. The entire
program is 6 lines:
start:
low 11 ' mosfet gate
pause 4000
hi 11 ' mosfet gate
pause 4000
goto start
The servos are wired, but the code does not address them. I'm hoping
that the two batteries will solve this problem too.
Dave
The servos are seeing short pusles and responding. I've seen this myself.
Go with the second battery.
Paul
> Some kind of magic is happening. My code is very basic. The entire
> program is 6 lines:
>
> start:
> low 11 ' mosfet gate
> pause 4000
> hi 11 ' mosfet gate
> pause 4000
> goto start
>
> The servos are wired, but the code does not address them.
> I'm hoping
> that the two batteries will solve this problem too.
brownout, but I still have the problem of the mosfet driving the BOE
servos. I have a powerpoint sketch which shows my circuit. How can
I
get this to you. I don't show the circuit for the servos, which use
p12 and p13. Both of them are being driven in the same direction,
but
only when the mosfet is switch Hi. I did notice that when they run,
they are running intermittent.
--- In basicstamps@y..., Paul Verhage <pverhage@s...> wrote:
> I'll bet it still the reset. Once the BS2 resets, its glitching
the
pins.
> The servos are seeing short pusles and responding. I've seen this
myself.
> Go with the second battery.
>
> Paul
>
> > Some kind of magic is happening. My code is very basic. The
entire
> > program is 6 lines:
> >
> > start:
> > low 11 ' mosfet gate
> > pause 4000
> > hi 11 ' mosfet gate
> > pause 4000
> > goto start
> >
> > The servos are wired, but the code does not address them.
> > I'm hoping
> > that the two batteries will solve this problem too.
browning out now because the prop motor isn't taking current from the main
battery. However, when you high and then low the mosfet for the prop motor,
the servos roll the BOE-BOT forward, even though, there is no code
concerning the servos. Ummmm......
Let me think about this.
Let's look at software issues. If you put a pause before the low 11, does
the BOE-BOT (BB) stay stationary? I want to make sure it's happening
because the mosfet is being turned on and off. Next, have you tried looping
the program so that all the BS2 does is keep pin 11 high? I want to see if
the BB behaves if the mosfet is kept continually on or off.
I have powerpoint in the classroom. You can send it as an attachment to
pverhage@s...
*****
I just thought of something. What if it's the mosfet that's drawing too
much current. Is there a current limiting resistor on the gate of the
mosfet? There should be a resistor between pin 11 and the gate of the
mosfet. This keeps the mosfet from drawing too much current from the BS2.
Try a 1k (brown, black,red) or 10k (brown, black, orange) resistor.
*****
Paul
> Here's the latest. I added the second battery, which eliminated the
> brownout, but I still have the problem of the mosfet driving the BOE
> servos. I have a powerpoint sketch which shows my circuit. How can
> I
> get this to you. I don't show the circuit for the servos, which use
> p12 and p13. Both of them are being driven in the same direction,
> but
> only when the mosfet is switch Hi. I did notice that when they run,
> they are running intermittent.
>
> --- In basicstamps@y..., Paul Verhage <pverhage@s...> wrote:
> > I'll bet it still the reset. Once the BS2 resets, its glitching
> the
> pins.
> > The servos are seeing short pusles and responding. I've seen this
> myself.
> > Go with the second battery.
> >
> > Paul
> >
> > > Some kind of magic is happening. My code is very basic. The
> entire
> > > program is 6 lines:
> > >
> > > start:
> > > low 11 ' mosfet gate
> > > pause 4000
> > > hi 11 ' mosfet gate
> > > pause 4000
> > > goto start
> > >
> > > The servos are wired, but the code does not address them.
> > > I'm hoping
> > > that the two batteries will solve this problem too.
>
>
>
>
> Your use of Yahoo! Groups is subject to
http://docs.yahoo.com/info/terms/
mosfet on and off, but don't have the prop motor attached. Now see if the
BB acts oddly. If it does, then the mosfet is drawing too much current from
the BS2.
Paul
turning in the same direction and they are mounted opposite.
Regarding the pause before the "low 11", once the program loops,
then it effectively has a pause before the low 11. I'm not sure
how to answer your question, but the servos mimic the propeller
motor exactly. If the prop motor is on, then the servos are running.
Regarding a continous loop through the "pin 11 hi", no I haven't
tried that. I'll try it tonight.
Since it seems that a signal is back driving the boe pin 15, would it
be helpful to add a diode between the mosfet gate and pin 15?
--- In basicstamps@y..., Paul Verhage <pverhage@s...> wrote:
> battery. However, when you high and then low the mosfet for the
prop motor,
> the servos roll the BOE-BOT forward, even though, there is no code
> concerning the servos. Ummmm......
>
> Let me think about this.
>
> Let's look at software issues. If you put a pause before the low
11, does
> the BOE-BOT (BB) stay stationary? I want to make sure it's
happening
> because the mosfet is being turned on and off. Next, have you
tried
looping
> the program so that all the BS2 does is keep pin 11 high? I want
to
see if
> the BB behaves if the mosfet is kept continually on or off.
>
> I have powerpoint in the classroom. You can send it as an
attachment to
> pverhage@s...
>
> *****
> I just thought of something. What if it's the mosfet that's
drawing
too
> much current. Is there a current limiting resistor on the gate of
the
> mosfet? There should be a resistor between pin 11 and the gate of
the
> mosfet. This keeps the mosfet from drawing too much current from
the BS2.
> Try a 1k (brown, black,red) or 10k (brown, black, orange) resistor.
> *****
>
> Paul
>
> > Here's the latest. I added the second battery, which eliminated
the
> > brownout, but I still have the problem of the mosfet driving the
BOE
> > servos. I have a powerpoint sketch which shows my circuit. How
can
> > I
> > get this to you. I don't show the circuit for the servos, which
use
> > p12 and p13. Both of them are being driven in the same direction,
> > but
> > only when the mosfet is switch Hi. I did notice that when they
run,
> > they are running intermittent.
solve the problem if indeed the mosfet is drawing to much power.
Dave
--- In basicstamps@y..., Paul Verhage <pverhage@s...> wrote:
> Here's how to test the mosfet. Disconnect the prop motor. Still
turn the
> mosfet on and off, but don't have the prop motor attached. Now see
if the
> BB acts oddly. If it does, then the mosfet is drawing too much
current from
> the BS2.
>
> Paul
> be helpful to add a diode between the mosfet gate and pin 15?
I don't think that's th eproblem. I think the BS2 is resetting itself.
Paul
copy of the schematic.
Paul
I figured it out. I replaced the radio shack motor with a light bulb and then
a different motor and found both to work without the servo feedback. Thus I
now believe the problem to be EMI or electro magnetic interference. Can you
think of a reason that this is not the case. When I added the reed solenoid, I
deduced that the two circuits were completely separated. The only conduction
would be electromagnetic.
Thanks for all your help. Look forward to hearing any final thoughts. You've
be a great help.
One final question. How can I modify the cheep RS motor to prevent it from
emitting the EMI?
Dave
--- Paul Verhage <pverhage@s...> wrote:
> > Since it seems that a signal is back driving the boe pin 15, would it
> > be helpful to add a diode between the mosfet gate and pin 15?
>
> I don't think that's th eproblem. I think the BS2 is resetting itself.
>
> Paul
>
>
>
>
> Your use of Yahoo! Groups is subject to http://docs.yahoo.com/info/terms/
>
>
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the motor terminals, tight against the motor, short leads. Some use a
scheme that is supposed to be better; They use caps from each motor
terminal to motor frame, again, tight against the motor.
Ray McArthur
>
> One final question. How can I modify the cheep RS motor to prevent it
from
> emitting the EMI?
> Dave
>
often do this on RC cars and kids motorized toys.
Original Message
> One final question. How can I modify the cheep RS motor to prevent it
from
> emitting the EMI?
> I figured it out. I replaced the radio shack motor with a
> light bulb and then
> a different motor and found both to work without the servo
> feedback.
Haahhhhh, indeed. Very good.
I wish I thought of that. I've only seen that once, but it was the servo
chattering, there was no rotation. Physical seperation is one way to reduce
that. They also make a ferrite bead that you might try.
Good catch.
Paul
> ceramic cap across
> the motor terminals,
The cap sends AC to ground, thus filtering it out. It's recommended for
ICs.
Paul
a +/- direction required, with respect to positive voltage?
--- In basicstamps@y..., Paul Verhage <pverhage@s...> wrote:
> > RC models (like electric boats and planes) use a 0.1 uf
> > ceramic cap across
> > the motor terminals,
>
> The cap sends AC to ground, thus filtering it out. It's recommended
for
> ICs.
>
> Paul
stops a constant AC. There's no + or - if you don't use electrolytic caps.
The 0.1 uF is small enough that there are no electrolytics.
Paul
>
Original Message
> From: cuz_hsv@y... [noparse]/noparse]mailto:[url=http://forums.parallaxinc.com/group/basicstamps/post?postID=7844kr32vIdDXjD_Hsvo0Ceb9Sp_JMN3u25vbLvi0mE2ihL8weCnAWWqow-bbMXc1-hupT2mhfZ27A]cuz_hsv@y...[/url
> Sent: Monday, March 05, 2001 8:46 AM
> To: basicstamps@yahoogroups.com
> Subject: [noparse][[/noparse]basicstamps] Re: Mosfet and Board of Education
>
>
> With the added cap, can I still change the motor direction? Is there
> a +/- direction required, with respect to positive voltage?
>
> --- In basicstamps@y..., Paul Verhage <pverhage@s...> wrote:
> > > RC models (like electric boats and planes) use a 0.1 uf
> > > ceramic cap across
> > > the motor terminals,
> >
> > The cap sends AC to ground, thus filtering it out. It's
> recommended
> for
> > ICs.
> >
> > Paul
>
>
>
>
> Your use of Yahoo! Groups is subject to
> http://docs.yahoo.com/info/terms/
>
>
frequencies. They are not polarized, so the motor can be run in either
direction.
Ray McArthur
Original Message
From: <cuz_hsv@y...>
To: <basicstamps@yahoogroups.com>
Sent: Monday, March 05, 2001 10:46 AM
Subject: [noparse][[/noparse]basicstamps] Re: Mosfet and Board of Education
> With the added cap, can I still change the motor direction? Is there
> a +/- direction required, with respect to positive voltage?
>