"The schematic is unambiguous. In fact, the my observations about W-, B- and RLED are nicely concentrated on page 2, in the "Virtual Ground Power Supply" schematic fragment."
I apologize, the schematic is indeed unambiguous, the problem occurs somewhere in the chain after the schematic, after my eyeballs, likely in the eyeball to back of head transfer process. But hey! I'm learning, right?
"You can trace this out on the board layout image. The only difference is that the "V-" logical signal label never appears."
That was the picture, sign, AND guy in a lab coat pointing that I needed since this where my blockhead phenomenon was kicking in.
"I've updated the board layout image to the current version. Previously I had a v0.5 image up there. There are only small differences between the two. I decided to update it more to remove a source of uncertainty than to fix a problem."
Great, I already printed it, I'll watch for an updated version. Thank you for the updates!
"I'm going to ignore those measurements until you confirm you're measuring against the real V-, or re-measure. You don't need to post them if they turn out to be spot-on after all."
Me too.
"Please show your work, Miss Engelstad.
"
Ha! I did on paper, I just didn't post it. I should have because I knew I was off by some factor of ten. Here is where my error was:
I used 85 instead of 0.085 because the part selection guide reads:
"The trickle charge current shouldn’t be more than 0.1C for NiMH cells. (E.g. 70 mA for 700 mAh cells.)" If I'd worked the formula there, I would have seen how to properly work the problem with different values. I blew past it the first time because didn't think I'd ever need to because I have very little experience with rechargeables and didn't even know they come in different mAh values. I got lazy. Here was my calculation:
R13 = (18 - 1.4) / 85 = .19
That didn't make any sense, so I tried recreating what might have been used with other battery.charger combos and got:
R13 = (16 - 1.4) / 70 = .2085
R13 = (12 - 1.4) / 70 = .1514
So, from that... I don't know what the hell I was thinking.
"So, a 200 or 220 ohm resistor would be the smallest I'd use. The stock 1K resistor you replaced would still have been okay, it would have just taken ~5x as long to fully trickle charge the battery that way. In practice, that's not going to be a problem in most cases. The trickle charger exists more to keep the battery topped up if you leave it connected to the charger overnight, so it's 100% ready to go when you unplug it to use it on battery the next day.
...
If you don't want to desolder this resistor again or don't have anything in the low hundreds on hand, a quick and easy option is to solder tack the 1K you removed on top of it, giving ~900 ohms."
I'm okay desoldering.... now. After many tears and frustrations and monies spent on desoldering guns and many destroyed boards, I finally learned to use braid. They key was your liquid flux. That's how I'm able to rework so much of my stuff. I build boards, look at them, get all obsessive, then decide, "CHANGES!" and redo them... I really like your boards, they are actually reworkable, the traces don't just lift off the boards like tinfoil. Man, I hate that. End digression.
"In an analog circuit, V- and ground are almost always different things. LNMP is no exception."
Well that nicely illustrates how much I know. I had that concept Perfectly Backwards.
"Your biggest clue was the IG pad hanging off that plane, which you can see from the schematic doesn't connect to V-."
I'll keep that in mind in the future, thanks.
Thank you Tangent. You get the prize today.