@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. ![Grin ;D](https://www.eevblog.com/forum/Smileys/default/xgrin.gif.pagespeed.ic.QVVz6XIT20.png)
mnem
![](https://www.eevblog.com/forum/testgear/test-equipment-anonymous-(tea)-group-therapy-thread/?action=dlattach;attach=1099846;image)
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 ![ThumbsUp :-+](https://www.eevblog.com/forum/Smileys/default/icon_smile_thumbsup.gif.pagespeed.ce._JElyJQqdB.gif)
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.
![Roll Eyes ::)](https://www.eevblog.com/forum/Smileys/default/rolleyes.gif.pagespeed.ce.XcUK202Yqt.gif)
![](https://www.eevblog.com/forum/testgear/test-equipment-anonymous-(tea)-group-therapy-thread/?action=dlattach;attach=1160626;image)
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.
![Tongue :P](https://www.eevblog.com/forum/Smileys/default/xtongue.gif.pagespeed.ic.J5mTe0A2NA.png)
mnem
"It's always somethin'..." ~Rosanne Rosanna-Danna