Stand by power WP 34s & HP 35s

[abaldoni]

(09-09-2014 07:10 PM)pito Wrote:  There is an another design "feature" with hp30b/wp34s/wp31s - the two cr2032 batteries are wired in parallel, without any isolation diodes. It means the "stronger" battery will always discharge itself into the "weaker" one.. And there are none two batteries equal..

Yes, however a diode drop would probably worsen the situation.
I didn't analyze the circuit, but from the behaviour while measuring currents, it seems to me that HP 35s actively switch from one battery to another every couple of seconds while on and idle (but stood on the same while running the loop program). I don't know what's happening in off state, probably it has normal diodes to power the processor enough for waking up and bypass them when on.

Best regards,
(Mr.) Andrea Baldoni