What I have discovered so far. The "5000mAh" pack contains the following components.
1) The USB LiPo Charger IC with the designation SC9017S
Probably a variant of this SE9017.2) The "blinkenlights" chip, unmarked. This is probably a common low power microcontroller which blinks a few LEDS and has an A/D pin to measure the state of charge. It could also be an off the shelf part designed to do the same job.
Pressing the "Power" button, simply wakes up this chip, to get it to blink the lights. The battery pack is actually permanently powered on, so sadly I can't simply hook in to the "magic power button" to switch the pack on and off, and thus control the camera.
3) An identical LiPo charge protection circuit to the NB-4L clone I talked about previously. This is also used in numerous other LiPo batteries, and consists of...
DW01 Plus One cell Lithium-ion/Polymer battery protection IC
8205A Dual mosfet Configured with the DW01 Plus, as per the DW01 Plus reference design.
4) Two
PT1301 High Efficiency Low Voltage Step-up DC/DC Converters (one for each of the USB outputs).
Note: The PT1301 chips are probably being driven quite hard, as they both look to be configured to produce 1A at 5V, contrary to the label printed on the case, which states one is 500mA and the other is 1A
Furthermore the 5V USB outputs have a tendency to shut down when I attach a camera + buck regulator to them, if the battery is anything less than fully charged. Since the camera may well draw >1.5A at startup this is not a great surprise.
5) A LiPo pack, which *may* be 5000mAh, but is suspiciously unmarked.
For my next trick, I need to tap in to the battery directly, as I don't actually need the 5V output, since I can power an Ixus directly from the 3.7V of the Lipo. This will extend the usable output time of the pack (currently it lasts about 4 to 5 times as long as a fully charged NB-4l). In theory if the NB-4L is 750mAh, I should be able to get about 6 to 7 times the running time of an NB-4L.
To do this initially I intend to solder a wire to the +Ve (red) battery terminal, and another to the solder pads on the ground plane next to the "power" button. This output will then be connected to a suitable socket on the pack, and a lead run from there to the dummy battery in the Ixus.
As I previously suggested, soldering directly to the -Ve output of the LiPo (the black wire) would be a bad move, as we would be on the wrong side of the mosfets used to protect the battery against over charge and discharge.
A future enhancement would be to add some sort of mosfet switch, opto switch or relay in line to allow a logic level signal to control the output. This would allow a microcontroller, pir or whatever to switch the camera on and off. This would let me preserve the battery by switching off the camera when not in use. This should allow for much longer running times, theoretically tens or even hundreds of times longer.
I think I may investigate using the
same dual mosfet as it seems to be perfect for switching at low voltages, and is available for a few pence.
EDIT: I bought a bunch of
these mosfets, so watch this space while I figure out how best to use them to switch the camera on and off. It'll probably be week or two before they arrive, and the "solar batteries" will in all probability be delivered first. Judging simply by the spec. of the dual mosfets, it should be a breeze to switch them on and off with anything >1.5V. They should be good for anything up to 20V, so 3v3 or 5v logic levels, from an arduino clone, or the output from a PIR should do the trick. Alternatively, the alarm signal from a digital alarm clock should also work.
If I can devise some feedback from the camera (switching on one of the LEDs being the obvious candidate), and OR the two signals together, I should be able to make an external event switch on the camera, and then let the camera decide when to switch itself back off again.
