Yup, the most frequent comment on Hackaday, “You could have used a 555 for that”. Well, I did. In fact, I used a pair of 555s …but probably not the sort you’re thinking of.
A few years back (see date-code photo, below), I found these batteries in a local equivalent of the “Dollar Store”. They only came in pairs, which made them more than twice as expensive as the normal, no-name AA alkaline cells, but with that branding I had to get at least one pack.
I used them (probably in one of my PIC projects back then) and then forgot about them, until I was scrambling to find some not-quite-so-dead batteries to check an ESP01S project a couple of weeks back and found them at the back of a drawer.
I popped the DVM probes on them (unloaded, of course) and was very surprised to see a healthy 1.5v reading.
Well okay, lets fire this thing up and see what happens! What happened was that the ESP01S blue LED flashed, then …nothing. Turning one of them upside-down, the date code reminded me that it was very many moons ago that I last used them.
They certainly didn’t owe me anything, but I wondered what the voltage had gone down to under load. Having had lots of experience with these el-cheapo batteries, I wasn’t at all surprised to see that the voltage across the cell swung well into negative territory when I held down the “On” switch. What still surprised me was that the voltage swung almost straight back to that “healthy” 1.5v reading once the load was removed. Usually these cells are hard-pressed to register a no-load voltage of 0.9 ~ 1.1v in their fully depleted states.
Maybe these we’re just catching their “second wind” …or maybe they do have a 555 hidden inside them after all!
The ESP01S board wouldn’t stay powered with these batteries in the pack, so I had to hold down the “On” switch long enough to snap the photo.
No ESP01S modules were harmed in the production of this blog post, but it probably didn’t do my poor little 555s much good.