9 May
2011
9 May
'11
7:26 p.m.
hi,
here v0.8 : https://gsm.tsaitgaist.info/SIMtrace/v0.8/
Compared to v0.7+, I added 2 1n4148 after the parallel voltage regulator
outputs.
I wanted to avoid the regulators to fuzz each other, but I don't know if
it's right. Maybe an additional zener diode is also required.
Now I'm looking for the parts and footprints.
Kevin
9 May
9 May
9:07 p.m.
Hi Kevin,
On Mon, May 09, 2011 at 07:26:58PM +0200, Kevin Redon wrote:
here v0.8 :
https://gsm.tsaitgaist.info/SIMtrace/v0.8/
Compared to v0.7+, I added 2 1n4148 after the parallel voltage regulator
outputs.
I wanted to avoid the regulators to fuzz each other, but I don't know if
it's right. Maybe an additional zener diode is also required.
I understand the intention, but I doubt it's a good idea. First, the
1N4148 is quite low-power/low-current, i.e. it will be the weakest
element in the chain. Second, it's a silicium diode and thus causes a
voltage drop of 0.7V, i.e. we will have 3.3-0.7= 2.6V only, which is
really bad.
I think you should just leave them out. You could simplify the design
by removing the DC/DC converter (SC120) and simply attach the battery
connector to the +5V input. The TPS73633 is a ultra-low-drop regulator,
i.e. from voltages >= 3.375V on it will provide a stable 3.3V output.
This means a battery pack with 3 or 4 1.2V cells should do just fine.
What do you think? We can save the step-up regulator and loose the
design risk of leaking power from the USB into the step-up regulator at
the same time...
Regards,
Harald
--
- Harald Welte <laforge(a)gnumonks.org> http://laforge.gnumonks.org/
============================================================================
"Privacy in residential applications is a desirable marketing option."
(ETSI EN 300 175-7 Ch. A6)
9:11 p.m.
Hallo Kevin.
here v0.8 :
https://gsm.tsaitgaist.info/SIMtrace/v0.8/
Compared to v0.7+, I added 2 1n4148 after the parallel voltage regulator
outputs.
I wanted to avoid the regulators to fuzz each other, but I don't know if
it's right. Maybe an additional zener diode is also required.
Hmm. The diodes will cause a voltage loss of about 0,7V ;-/ Maybe you
will need something more tricky or just add a little switch. I think
nobody will change the power supply method every minute.
regards.
Philipp
--
______________________________________
Philipp Fabian Benedikt Maier
philipp.maier(a)runningserver.com
Funk: DO5DXT
http://www.runningserver.com
http://www.diskettenschlitz.de
______________________________________
9:18 p.m.
Hi!
Or maybe you could do this:
3xMigon ----->|------+ +--------+
| | |
+----------+ 3,3V +--------
| | Reg. |
USB 5V ----->|------+ +---+----+
|
_|_
Simple, but effective ;-) And you need only one regulator.
regards.
Philipp
--
______________________________________
Philipp Fabian Benedikt Maier
philipp.maier(a)runningserver.com
Funk: DO5DXT
http://www.runningserver.com
http://www.diskettenschlitz.de
______________________________________
10 May
10 May
9:57 a.m.
then it would be 4xAAA/AA (3xAA will only work if fully charged)
the other idea would be :
0.7-4.5 --- VREG 5V --->|----+
|
+--- VREG 3.3V
|
USB 5V ---------------->|----+
or another nice idea (like the arduino does for the 5v) :
BATT --- VREG 3.3V ---+
|
FDN304 -- 3.3V
|
VUSB --- VREG 3.3V ---+
as you wish,
Kevin
On 09.05.2011 21:18, Philipp Fabian Benedikt Maier wrote:
Hi!
Or maybe you could do this:
3xMigon ----->|------+ +--------+
| | |
+----------+ 3,3V +--------
| | Reg. |
USB 5V ----->|------+ +---+----+
|
_|_
Simple, but effective ;-) And you need only one regulator.
regards.
Philipp
5:11 p.m.
Hi Kevin,
On Tue, May 10, 2011 at 09:57:29AM +0200, Kevin Redon wrote:
then it would be 4xAAA/AA (3xAA will only work if
fully charged)
fine with me. I honestly don't care about the number of batteries...
and the PCB will not be smaller than 4x AAA/AA anyway.
the other idea would be :
0.7-4.5 --- VREG 5V --->|----+
|
+--- VREG 3.3V
|
USB 5V ---------------->|----+
that should work, but you should use something like a 1N4001 as the
diode, to cope with more current. However, I would want to have that
tested on a breadboard before sending the gerber off for PCB
manufacturing, just to make sure the power supply side is working. We
still have a problem if somebody decides USB _and_ the battery power
supply :/
In fact, now that I'm thinking off it, we should use one of those jacks
which disconnnect one contact when plugging in the power supply. This
way we can actually interrupt the USB 5V once a power supply plug has
been plugged in. This should be done independent of the decision on the
voltage regulator.
or another nice idea (like the arduino does for the
5v) :
looks not that trivil to me, as you don't only need the FDN304 but also
the LM358 op-amp and external circuitry. Probably a bit overkill.
So I think we should route the 5V USB via the power plug, and simply use
a low-drop-out 3.3V regulator, like in the current schematics. This way
the LDO input will be USB 5V _until_ somebody plugs in an external power
supply or battery pack, which will have to provide at least 3.4V for
stable operation.
Regards,
Harald
--
- Harald Welte <laforge(a)gnumonks.org> http://laforge.gnumonks.org/
============================================================================
"Privacy in residential applications is a desirable marketing option."
(ETSI EN 300 175-7 Ch. A6)
12 May
12 May
10:14 a.m.
I'm back.
I was looking around for a solution for such a trivial task (power
switching), and there is no easy answer.
not effective.
agree
that is the decision I took. Simple, cost effective, saves place.
the other idea
would be :
0.7-4.5 --- VREG 5V --->|----+
|
+--- VREG 3.3V
|
USB 5V ---------------->|----+
In fact, now that I'm thinking off it, we should use one of those jacks
which disconnnect one contact when plugging in the power supply. This
way we can actually interrupt the USB 5V once a power supply plug has
been plugged in. This should be done independent of the decision on the
voltage regulator.
most dc jack can provide such a solution, but I think the USB 5v should
be used if the two sources are connected. USBVCC is more stable,
moreover if the user leaves it connected the battery will be drained.
Another point is that the normally closed circuit uses the barrel
(normally the jack is used to plug wall power, cutting the board battery
line). Having +5v on the barrel is not common (if the user has an
of-the-self power adaptor).
or another nice idea (like the arduino does for
the 5v) :
looks not that trivil to me, as you don't only need the FDN304 but also
the LM358 op-amp and external circuitry. Probably a bit overkill.
So I think we should route the 5V USB via the power
plug, and simply use
a low-drop-out 3.3V regulator, like in the current schematics. This way
the LDO input will be USB 5V _until_ somebody plugs in an external power
supply or battery pack, which will have to provide at least 3.4V for
stable operation.
yes, I also like this solution, but has drawbacks (see above)
I found two other solutions :
- using a automatic power switching mux (TPS2115). too expensive and
take to much space.
- using a manual switch to select the power source
then it would be 4xAAA/AA (3xAA will only work if
fully charged)
fine with me. I honestly don't care about the number of batteries...
and the PCB will not be smaller than 4x AAA/AA anyway.
that should work, but you should use something like a
1N4001 as the
diode, to cope with more current
1N5819 allows 1A, it should be enough.
1N4001 has a forward voltage of 1.0V, 1N5819 only 0.6-0.7V.
here the schema : https://gsm.tsaitgaist.info/SIMtrace/v0.9/
I now an doing the BOM. I'm half-way through, but it takes time.
Kevin
5268
days inactive
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6 comments
3 participants
participants (3)
-
Harald Welte -
Kevin Redon -
Philipp Fabian Benedikt Maier