What enables 50G to power over USB?
DrPop
information. Perhaps someone on here knows this?
What exactly is different about the 50G that allows it to accept an
incoming power over the USB port, that the 49G+ cannot? I have this
idea I'd like to try for an accessory...but it may only work with the
50G.
Also, from the documentation, it appears that the 50G's serial port
has a "power" level connection at the serial port. Do all the 49
series serial ports work this way too? I mean, have a pin for power
out/in on their serial ports as well, or is this a new feature of the
50G alone? I'm thinking 49G, 48gII and 50G?
I realize the original 48S/SX G/GX all have only 4 pins, and no
obvious way to connect to the battery (I would love to be enlightened
about this, but after looking at the pinout diagram, I just don't see
how we can tap into the battery easily on the original 48 series.)
Thank you for any discussion on this.
bokubob
> What exactly is different about the 50G that allows it to accept an
> incoming power over the USB port, that the 49G+ cannot? I have this
> idea I'd like to try for an accessory...but it may only work with the
> 50G.
I'm not sure quite what your after, but maybe something on my page
about hacking the usb power on the 49g+ would help you out?
http://sites.google.com/site/jeisch/hp-49gplus
-Jonathan
Andreas Möller
> What exactly is different about the 50G that
> allows it to accept an incoming power over the
> USB port, that the 49G+ cannot?
It is a hardware feature that is not available in the HP 49G+.
> to accept an incoming power over the USB port
Note that the machine must be “off” for switching to USB power.
If you install my ROM enhancement (aka MLP aka Multi Lingual Pack) and
activate the enhanced status screen you will also see the current
status of the battery or USB if the cable is plugged in and active.
Here is an example showing the battery status in the status screen of
the German version, this feature is available in all language versions
(English, Italian, Spanish, French and German):
HP 50G Multi Lingual Pack Deutsch
http://www.youtube.com/watch?v=FBEs6ReIJOE
> the 50G's serial port
Note that it is not a true RS-232 interface.
> Do all the 49 series serial ports work this way too?
On all ARM based machines the serial port comes from SAMSUNG's
ARM920T, so they are all the same.
Regards,
Andreas
http://www.software49g.gmxhome.de
Joel Koltner
news:54721872-a8da-447f...@m20g2000prc.googlegroups.com...
> I realize the original 48S/SX G/GX all have only 4 pins, and no
> obvious way to connect to the battery (I would love to be enlightened
> about this, but after looking at the pinout diagram, I just don't see
> how we can tap into the battery easily on the original 48 series.)
The "ground" (pin 4) on the HP-48's serial port is actually the battery's
positive rail! -- The transmitted data line, then, actually swing between
battery ground and... something like +7.5V -- some higher voltage they already
had to create to drive the LCD -- so that a connected device sees (more or
less) +/-3V.
---Joel
John H Meyers
> Also, from the documentation, it appears that the 50G's serial port
> has a "power" level connection at the serial port. Do all the 49
> series serial ports work this way too? I mean, have a pin for power
> out/in on their serial ports as well, or is this a new feature of the
> 50G alone? I'm thinking 49G, 48gII and 50G?
The original 49G (Saturn CPU, not ARM emulated),
in early production runs (such as both of mine),
had a fundamental circuit error in its serial port,
dubbed the "serial port bug."
I don't quite remember, but seem to dimly recall
that _both_ battery leads might go to that connector,
and that if so, some unfortunate poking around
in the recesses of that connector might provoke some fireworks.
The "buggy" serial ports also had signal voltage or current levels
which were out of spec -- some robustly engineered
serial devices could still work with it,
while others could not communicate at all.
Documents about the 49G Serial Port Bug,
thanks to Eric Rechlin's great site and its contributors:
http://www.hpcalc.org/search.php?query=serial+port+bug&hp49=1
-[ ]-
DrPop
especially the part about the ground pin on the 48 series going to the
battery. I don't want to get too far ahead of myself, but I have some
ideas of a project for charging the batteries in a unique way...so the
accessory must connect to the power source - also, I would like ot
design something that uses power as well, so if I could tap into the
on board batteries as well, it would be simpler to create.
What I'm still not certain of, is why can the HP50G get a power in
over the USB, and the 49G+ cannot? I don't understand what is unique
about the 50G that lets it do this.
Al Borowski
> What I'm still not certain of, is why can the HP50G get a power in
> over the USB, and the 49G+ cannot? I don't understand what is unique
> about the 50G that lets it do this.
Without a circuit diagram I'm only guessing, but there are a few ways
to do this.
The easiest way would be to use a pair of low voltage drop diodes,
joined at the cathode, to power the calculator. The anode of one goes
to the AAA batteries, the other to the +5V USB supply. Whatever supply
is higher powers the calculator. This is a pretty bad idea because you
are now losing a diode drop of supply when running normally (say
goodbye to maybe 10% of your battery life for a feature only 1% of
people will use).
A more intelligent way is to use electronics to actively switch from
one supply to the other. The calculator knows when it is plugged into
a USB port. What I'd do is use a handful of transistors to let the
calculator decide where it wants to be powered from. When the
calculator is first turned on power flows from the batteries, through
a diode, to a switchmode supply. The processor then says 'Yep, I want
to run on batteries' and turns on a P-channel FET which has been
placed in parallel with that diode, shorting it out and reducing the
voltage drop to insignificant levels. Later on someone plugs it into a
USB port. The battery FET first turns off, then a little while later
another FET turns on and connects the switchmode supply to the USB
rail. The battery diode prevents the batteries being charged with the
wrong voltage.
If you want I can sketch up a schematic later. I can probably think of
a much better way later as it's midnight and I've only put 30 seconds
thought into it.
Cheers,
Al