A weird idea for Boebot add-on
I was swapping out some dead AAs for a 9v on my BOE the other day and I
had an idea that it'd be nice to be able to have both the AAs and a 9v connected
and have some kind of "detector" to see when one gets low then automatically
switch over to the other.
I'm pretty much a newbie at electronics, but I think this would be kinda nice to
have and pretty cheap to make. It'd require a custom PCB but I think it'd be
worth it.
Basicly I think a voltage trigger... like those used to control BEAM bots with
a few transistors should be enough to detect when a battery is getting low
(say, below 5.5v or whatever would be too low for a BOE's voltage regulator
to convert into a stable +5v) and automatically break connection with that
battery then switch to the other.
This would allow you to double the lifespan of the average BOE application.
A high farad (Maybe 3300uF or something along those lines) capacitor could
make the switch-over seamless so that the stamp doesn't reset.
Since the 9v and barrel jack are "Mechanically seperated" by the fact that
you can't fit both on at once, you'd need to have it plug into both and
have two jacks of its own on-board.
Anyways, it was just an idea. What do you guys think?
had an idea that it'd be nice to be able to have both the AAs and a 9v connected
and have some kind of "detector" to see when one gets low then automatically
switch over to the other.
I'm pretty much a newbie at electronics, but I think this would be kinda nice to
have and pretty cheap to make. It'd require a custom PCB but I think it'd be
worth it.
Basicly I think a voltage trigger... like those used to control BEAM bots with
a few transistors should be enough to detect when a battery is getting low
(say, below 5.5v or whatever would be too low for a BOE's voltage regulator
to convert into a stable +5v) and automatically break connection with that
battery then switch to the other.
This would allow you to double the lifespan of the average BOE application.
A high farad (Maybe 3300uF or something along those lines) capacitor could
make the switch-over seamless so that the stamp doesn't reset.
Since the 9v and barrel jack are "Mechanically seperated" by the fact that
you can't fit both on at once, you'd need to have it plug into both and
have two jacks of its own on-board.
Anyways, it was just an idea. What do you guys think?
Comments
A simpler system would be to use a 6V AAA battery pack for the "backup" supply and a 7.2V NiMH battery pack (6 cells) for the primary supply. Each would have a Shottky diode in series with the (+) lead so the battery with the highest voltage would supply the BoeBot, but you wouldn't lose too much voltage in the diodes. NiMH batteries tend to keep their voltage stable until the are nearly exhausted, so the NiMH battery pack would supply the BoeBot until nearly exhausted, then its voltage would rapidly drop to below the 6V of the "backup" supply which would take over to supply the BoeBot. The BoeBot could monitor its input supply voltage (see www.emesystems.com for an example) and switch to a low power mode when the input voltage dropped to 6V.
I really kind of wanted a self-contained unit though. I wouldn't want to take up more I/O pins than needed... I'm assuming
by the www.emesystems.com example you meant the RCTIME section (Which was amazing by the way).
I knew about the NiMH batteries keeping their voltage up then suddenly dropping right before they die. That's kinda what I
was counting on. When they started that sudden drop, the circuit would switch to the backup, using a capacitor to keep the
BS2 and all attached devices running for the few ms needed to switch power supplies over.
This was just an ideal thought and I don't have nearly enough knowledge of electronics to attempt this. I just thought I'd
toss the idea out to whoever might be able to actually use it.
I'd actually like to see something like this sold by parallax. I know they don't really push Stamp-based products anymore,
but it would help those of us who do own a BOE.
I'd buy one [noparse]:)[/noparse]
If you don't want to use I/O pins for a voltage monitor, you can easily build a battery monitor that will light an LED or sound a buzzer when the main battery voltage drops below a set threshold (www.elecfree.com/electronic/low-voltage-battery-monitor-by-lm339/). I just found this by doing a Google search with "battery monitor". You can find all sorts of other battery monitor circuits the same way. Here's one that can even do the switching itself of up to 150mA (www.intersil.com/cda/deviceinfo/0,0,ICL7673.html). It comes in a PDIP package and you might be able to get samples. Download and read the datasheet. It shows sample circuits. You could easily wire this up on the BOE breadboard.
My robot is now currently working off the 2 9-V and a 7.6 RC battery. It should not be that hard to construct a current switch to enable a new battery.
Hey, a new idea for a project !