@mnementh I also looked at one of these calculator kits last year and decided against it, however I may just review that decision to break the boredom up.
Well... that was satisfying, but not nearly long enuf. All the actual "make"-ery is done... now it's just assembly. I might mod it with a an old camera Li-Ion cell tho; it appears to have a backlit LCD & I don't imagine CR2032s will last long. Still... def worth the pittance they charge to occupy a afternoon.
mnem
Yeh, it does make you wonder as to why they didn't include a power socket and make the batteries rechargeable, shouldn't add all that much to the kits cost?
Seeing it all sitting there now, kinda makes me wish I had one to build to... I may have to pull the trigger on one myself soon
Ugghhh... no runsies on single LiPo. While STC15W408AS processor runs down to 2.4V, the cheap 1602A LCD still requires min 4.7V to operate. That explains the choice of 2 CR2032s as power source. While everything does run off a 7550-1 5V LDO which can easily be powered with a 2S LiPo, then BMS becomes a bit more complicated, as the tiny micro-USB all-in-one BMS boards only do a single cell. They do make 2S versions, but much larger and I only have the 1S version on hand.
Trying to decide if I really give even half a rat's ass on this toy... Measured total current draw is 16.5mA operating, 9-10uA quiescent. Figuring approx 160-170mAH capacity on a CR2032 (down to 2.8V*2 or so for the 5V LDO) that's still a solid 2 years standby give or take, which seems pretty good... except the operating draw is aboot 100x the CC a CR2032 is designed for, and more than twice the expected pulse current.
I'm still looking for some actual stats at a 16mA draw; everything with useful figures has been for pulse loading in the uS-mS range, not continuous for many seconds or minutes at a time. At this point, no idea how such a high current draw will affect actual capacity in mAH... but I would be surprised if actual yield is more than double-digits.
mnem
"It's always somethin'..." ~Rosanne Rosanna-Danna