Device on/off

Archiver

I am using an BS2pe to acquire a GPS position every hour. To save
battery power the unit sleeps between fixes. I also plan to use a
reed switch to power the unit up. So I have incorporated the
suggested circuit given here:
http://www.angelfire.com/wizard/y2kbc/STAMPS/lps.gif

This works with a BS2 but I am having problems with both a BS2p and a
BS2pe. Is this something to do with the current draw? Do I need
different transistors?
Also, when the unit sleeps the I/O pin goes low and switches the
power off. I have tried putting a 10uF cap between the I/O and
ground but this does not seem to help. I have also tried a 4K7 pull-
up resistor but then the Stamp cannot switch itself off.

Any suggestions?

Thanks,
Helen

Archiver

Hi Helen

referring to:
>http://www.angelfire.com/wizard/y2kbc/STAMPS/lps.gif


That circuit with the capacitor on the i/o pin to hold it on would
work if you substitute a mosfet like the VN10 for the 2N1304 npn
transistor. As it is, the 2.2k and the base circuit drains off the
capacitor too fast. The circuit might work as it is if you
substitute a 100k resistor for the 2.2k, and include a >~1uF
capacitor on the pin. Also, I suggest that you leave out the second
transistor labeled "to other supplies", because it robs base current
from the 2N3906 that is supposed to supply current to the Stamp. {If
you do use two transistors like that, glue them together so they will
be at the same temperature and attempt to match their Vbe's.}

Some voltage regulators have a shutdown pin that can be used in this
manner. For example, there is an 8-pin LT1121 regulator on the
recent stamp modules, and that regulator turns off if its pin 5 is
pulled low by a resistance less than about 50kohms.

Note that the wake-up glitch (where the pins turn briefly to inputs)
is much shorter on the BS2pe than it is on the other Stamps, and thus
much easier to filter out. 0.1 millisecond as opposed to 16
milliseconds.

-- Tracy


>I am using an BS2pe to acquire a GPS position every hour. To save
>battery power the unit sleeps between fixes. I also plan to use a
>reed switch to power the unit up. So I have incorporated the
>suggested circuit given here:
>http://www.angelfire.com/wizard/y2kbc/STAMPS/lps.gif
>
>This works with a BS2 but I am having problems with both a BS2p and a
>BS2pe. Is this something to do with the current draw? Do I need
>different transistors?
>Also, when the unit sleeps the I/O pin goes low and switches the
>power off. I have tried putting a 10uF cap between the I/O and
>ground but this does not seem to help. I have also tried a 4K7 pull-
>up resistor but then the Stamp cannot switch itself off.
>
>Any suggestions?
>
>Thanks,
>Helen

Archiver

At 02:17 PM 2/13/04 +0000, you wrote:
>I am using an BS2pe to acquire a GPS position every hour. To save
>battery power the unit sleeps between fixes. I also plan to use a
>reed switch to power the unit up. So I have incorporated the
>suggested circuit given here:
>http://www.angelfire.com/wizard/y2kbc/STAMPS/lps.gif
>
>This works with a BS2 but I am having problems with both a BS2p and a
>BS2pe. Is this something to do with the current draw? Do I need
>different transistors?
>Also, when the unit sleeps the I/O pin goes low and switches the
>power off.

Helen,
I'm confused... The whole idea of this circuit is so that the
Stamp can turn itself off. You should not be using the sleep command.
The ONLY way that the Stamp should turn itself on in this configuration
is from an external source.

Perhaps I should explain the "second" 2N3906 with the label "To Other
Supplies" more clearly. This is to power ANYTHING else that may be connected
through an I/O to the stamp. By doing this you can avoid any parasitic
supply voltage that could enter the stamp through an I/O when it is off. As
it is, the GROUND parasitic helps to keep the 2N3904 "off".

-Beau Schwabe

> I have tried putting a 10uF cap between the I/O and
>ground but this does not seem to help. I have also tried a 4K7 pull-
>up resistor but then the Stamp cannot switch itself off.
>
>Any suggestions?
>
>Thanks,
>Helen

Archiver

Hi Tracey,

Thanks for the help. I removed the second transistor and it is now
working with a 10uF cap. I am already using the LT1121 as the power
supply to the GPS receiver - it is a really useful device.

Thanks again,
Helen

--- In basicstamps@yahoogroups.com, Tracy Allen <tracy@e...> wrote:
> Hi Helen
>
> referring to:
> >http://www.angelfire.com/wizard/y2kbc/STAMPS/lps.gif
>
>
> That circuit with the capacitor on the i/o pin to hold it on would
> work if you substitute a mosfet like the VN10 for the 2N1304 npn
> transistor. As it is, the 2.2k and the base circuit drains off the
> capacitor too fast. The circuit might work as it is if you
> substitute a 100k resistor for the 2.2k, and include a >~1uF
> capacitor on the pin. Also, I suggest that you leave out the
second
> transistor labeled "to other supplies", because it robs base
current
> from the 2N3906 that is supposed to supply current to the Stamp.
{If
> you do use two transistors like that, glue them together so they
will
> be at the same temperature and attempt to match their Vbe's.}
>
> Some voltage regulators have a shutdown pin that can be used in
this
> manner. For example, there is an 8-pin LT1121 regulator on the
> recent stamp modules, and that regulator turns off if its pin 5 is
> pulled low by a resistance less than about 50kohms.
>
> Note that the wake-up glitch (where the pins turn briefly to
inputs)
> is much shorter on the BS2pe than it is on the other Stamps, and
thus
> much easier to filter out. 0.1 millisecond as opposed to 16
> milliseconds.
>
> -- Tracy
>
>
> >I am using an BS2pe to acquire a GPS position every hour. To save
> >battery power the unit sleeps between fixes. I also plan to use a
> >reed switch to power the unit up. So I have incorporated the
> >suggested circuit given here:
> >http://www.angelfire.com/wizard/y2kbc/STAMPS/lps.gif
> >
> >This works with a BS2 but I am having problems with both a BS2p
and a
> >BS2pe. Is this something to do with the current draw? Do I need
> >different transistors?
> >Also, when the unit sleeps the I/O pin goes low and switches the
> >power off. I have tried putting a 10uF cap between the I/O and
> >ground but this does not seem to help. I have also tried a 4K7
pull-
> >up resistor but then the Stamp cannot switch itself off.
> >
> >Any suggestions?
> >
> >Thanks,
> >Helen

Archiver

Hi Beau,

Just to clarify - the unit sleeps between hourly GPS fixes but also
needs to be able to switch itself off if it receives a command from
the RS232 connection. I removed the second transistor and put a 10
uF cap on the I/O and the system is now working fine.

Thanks for the help.
Helen

--- In basicstamps@yahoogroups.com, "Beau Schwabe" <bschwabe@a...>
wrote:
> At 02:17 PM 2/13/04 +0000, you wrote:
> >I am using an BS2pe to acquire a GPS position every hour. To save
> >battery power the unit sleeps between fixes. I also plan to use a
> >reed switch to power the unit up. So I have incorporated the
> >suggested circuit given here:
> >http://www.angelfire.com/wizard/y2kbc/STAMPS/lps.gif
> >
> >This works with a BS2 but I am having problems with both a BS2p
and a
> >BS2pe. Is this something to do with the current draw? Do I need
> >different transistors?
> >Also, when the unit sleeps the I/O pin goes low and switches the
> >power off.
>
> Helen,
> I'm confused... The whole idea of this circuit is so that
the
> Stamp can turn itself off. You should not be using the sleep
command.
> The ONLY way that the Stamp should turn itself on in this
configuration
> is from an external source.
>
> Perhaps I should explain the "second" 2N3906 with the
label "To Other
> Supplies" more clearly. This is to power ANYTHING else that may be
connected
> through an I/O to the stamp. By doing this you can avoid any
parasitic
> supply voltage that could enter the stamp through an I/O when it is
off. As
> it is, the GROUND parasitic helps to keep the 2N3904 "off".
>
> -Beau Schwabe
>
> > I have tried putting a 10uF cap between the I/O and
> >ground but this does not seem to help. I have also tried a 4K7
pull-
> >up resistor but then the Stamp cannot switch itself off.
> >
> >Any suggestions?
> >
> >Thanks,
> >Helen