power saving methods, new to servos

Archiver

I'm thinking of building a battery powered device where I wan't the
stamp to take measurements from other ICs and move servos perhaps
once a day. To save power I'll put the stamp in sleep mode, and i'd
like to cut power off to the other components when they are not in
use. My first thought is to use a transistor triggered from a stamp
pin to control power to the extra devices, but the sleep command will
momentarily interupt any output signal going to the transistor every
2.3 seconds. Could I put a capacitor at the output so that the
transisotr wouldn't see the momentary interuption? Any better ideas
on how to cut power to the extra parts when they are not in use?

Also, this is my first time to use hobby servos with the pulseout
command, when I stop sending the pulseout command, will the servo
stay where it is or will it go back to center?

thanks,
Stew

Archiver

The servo will act as though it is unpowered once the signal
is taken away. This means that the servo will return to the
position that has the least amount of force on it.
--
Regards

Dave Evartt
American Hovercraft

Archiver

At 05:21 PM 11/7/03 +0000, you wrote:
>I'm thinking of building a battery powered device where I wan't the
>stamp to take measurements from other ICs and move servos perhaps
>once a day. To save power I'll put the stamp in sleep mode, and i'd
>like to cut power off to the other components when they are not in
>use. My first thought is to use a transistor triggered from a stamp
>pin to control power to the extra devices, but the sleep command will
>momentarily interupt any output signal going to the transistor every
>2.3 seconds. Could I put a capacitor at the output so that the
>transisotr wouldn't see the momentary interuption? Any better ideas
>on how to cut power to the extra parts when they are not in use?
>
>Also, this is my first time to use hobby servos with the pulseout
>command, when I stop sending the pulseout command, will the servo
>stay where it is or will it go back to center?
>
>thanks,
> Stew


I have done this in the past... basically you have the right idea.
Assuming that any of the external circuits will not need power as
long as the stamp is sleeping. Connect a bias resistor 100K or so
across the BE junction of your transistor(s) so that a "floating"
state on any of the stamp I/O's will be pulled to ground and keep
your transistor off. Then, instead of "cutting" power to the
device from your stamp, "supply" power to the device by powering
the stamp I/O pin. Don't forget your current limiting resistor
between the Stamp pin and the Base of the transistor.


-Beau Schwabe

Archiver

>I'm thinking of building a battery powered device where I wan't the
>stamp to take measurements from other ICs and move servos perhaps
>once a day. To save power I'll put the stamp in sleep mode, and i'd
>like to cut power off to the other components when they are not in
>use. My first thought is to use a transistor triggered from a stamp
>pin to control power to the extra devices, but the sleep command will
>momentarily interupt any output signal going to the transistor every
>2.3 seconds. Could I put a capacitor at the output so that the
>transisotr wouldn't see the momentary interuption? Any better ideas
>on how to cut power to the extra parts when they are not in use?
>
>Also, this is my first time to use hobby servos with the pulseout
>command, when I stop sending the pulseout command, will the servo
>stay where it is or will it go back to center?
>
>thanks,
> Stew


Hi Stew,

The capacitor idea works fine for me. On the most of the Stamps, the
interruption is about 18 milliseconds, so the capacitor has to hold
the transistor ON (or OFF as the case may be) for that length of
time. (The interruption on the BS2pe is only 0.1 millisecond, in
contrast to the other Stamps). I usually use an IC voltage regulator
for this purpose, instead of a transistor. The LT1121 turns off
when its "shutdown" line is pulled low, and turns on when SD\ is
pulled high or left floating.

-- Tracy

Archiver

Thanks guys for the help. I like the second regular method the best
I think. I'm using a BS2p so the capacitor won't have to be too big.

thanks,
stew

>
> Hi Stew,
>
> The capacitor idea works fine for me. On the most of the Stamps,
the
> interruption is about 18 milliseconds, so the capacitor has to hold
> the transistor ON (or OFF as the case may be) for that length of
> time. (The interruption on the BS2pe is only 0.1 millisecond, in
> contrast to the other Stamps). I usually use an IC voltage
regulator
> for this purpose, instead of a transistor. The LT1121 turns off
> when its "shutdown" line is pulled low, and turns on when SD\ is
> pulled high or left floating.
>
> -- Tracy