I have a small ATtiny84 running a simple project. Nothing amazing.
However, this project is powered by a shared 5v supply from a 230v to 5v PSU module.
I would like to design some kind of PCB that would charge a backup battery from this 5v supply, and switchover to it seamlessly if that 5v drops out.
Rather than some boost converter bodge or similar, I was looking to actually design a single pcb with maybe a NimH battery on board (rather than a temperamental fire hazard LiPo).
Thoughts? I have had a Google and drawn a blank so far on suitable circuits or IC's.
There is an IC I have used before for the switching ( ICL7673CBAZA). Maybe that is a starting point.
I imagine I either charge a larger voltage battery with some kind of boosting circuit, then drop that to a nice 5v, or I charge a samller capacity battery and boost it.
No. It needs 5v. Might get away with 4.5v if it runs OK on that (no particular load on the processor), but the OLED 128x32 screen attached is 5v (but it would run on 4.5v I imagine).
There is a circuit on the datasheet for the ICL7673. Not sure what components it needs for charging the battery.
You won't even need a super capacitor I don't think, how long does it take to write to EEPROM? Less than a second I think. Probably 4700μF would be plenty.
This Oled appears to be 5v only... can't see a regulator.
I don't want it to cut it super fine (as in a second or so). Also, it would have been nice to have a bit longer to maybe deduce why the original 5v has been lost in the first place.
I will have a play
I don't really want to dismantle the project just to get the screen out. Even if there is a regulator under the screen side (which is glued down), I am not starting to modify the screens to get over the power supply issue.
I have some other 128x64 screens here that do have the reg on the back. But it's not on the back of this 128x32
I was trying to configure the 'Typical circuit' on the first page to use a 5v supply to trickle charge a pair of Nimh batteries.
Therefore the battery pack it would be charging consists of 2x 1.2v 4.5Ah NimH cells (The batteries have to be at least 1.5v lower than the supply).
The cells I have here are 420mA x 16hrs for trickle charging.
Setting PGM0 and PGM1 is obvious enough (number of cells).
Not sure what R1 is supposed to be (High thermal limit trip?).
Not sure I understand the RSense value either. Would love to understand this stuff!
Especially annoying that the spec sheet says it's an easy to use IC. Not for me!
After a couple of years experience, you will probably understand it.
A lot of such devices are designed to be built into equipment by experienced electronic engineers. The designers\manufacturers of such devices rarely produce easy to follow tutorials.
