I've read quite a bit this afternoon about replacing the battery on an A4000D with a CR-2032 and general consensus of opinion seems to be that it doesn't work because by the time you have the lower (3v) battery in the first place, and then the forward voltage drop of a diode to prevent charging the resultant voltage is too borderline for the RTC chip to maintain it's memory.
So I looked at the schematics for the 4000-CR and that shows a standard 1N4148 diode fitted in the event that a Lithium battery is used and the data sheet for the RTC gives a minimum voltage requirement to store of 2.2v, so those two things back that up (3v - 0.65 = 2.35v = barely enough).
So then I figured 2 x CR2032 = 6v, but that's too much as although the absolute max for the RTC is 7v, that's a momentary 7v, not sustained.
Is there anything wrong however with simply using 2 x CR2032 in series + 1 x 1N4148 and of course the 1N4148 that is already in place to give me round about a 4.7v supply to the RTC. Seems fair to me but am I over looking anything? I would also be reducing the internal resistance of the overall battery pack as well so in theory the drop off didn't ought to be quite as severe as it's known to be on CR2032's either, though I'm not overly concerned about that.
---------- Post added at 16:17 ---------- Previous post was at 16:12 ----------
Oh, just to pre-empt the "why don't I just buy a 3.6v battery" question...
Can't buy anything like that around here and I'd have to order it in. I already have CR2032's, holders, 1N4148 diodes and indeed, IF I need it (don't think I do), breadboard all to hand.
So I looked at the schematics for the 4000-CR and that shows a standard 1N4148 diode fitted in the event that a Lithium battery is used and the data sheet for the RTC gives a minimum voltage requirement to store of 2.2v, so those two things back that up (3v - 0.65 = 2.35v = barely enough).
So then I figured 2 x CR2032 = 6v, but that's too much as although the absolute max for the RTC is 7v, that's a momentary 7v, not sustained.
Is there anything wrong however with simply using 2 x CR2032 in series + 1 x 1N4148 and of course the 1N4148 that is already in place to give me round about a 4.7v supply to the RTC. Seems fair to me but am I over looking anything? I would also be reducing the internal resistance of the overall battery pack as well so in theory the drop off didn't ought to be quite as severe as it's known to be on CR2032's either, though I'm not overly concerned about that.
---------- Post added at 16:17 ---------- Previous post was at 16:12 ----------
Oh, just to pre-empt the "why don't I just buy a 3.6v battery" question...
Can't buy anything like that around here and I'd have to order it in. I already have CR2032's, holders, 1N4148 diodes and indeed, IF I need it (don't think I do), breadboard all to hand.
