I’m working on a simple little project (ESP01S-based) right now which needs to be able to sense a warm body nearby, so naturally I turned to my stock of IKEA OLEBY sensor lights (having hacked several in the past and having been impressed with their all round, mmm …cheapness). For such a bargain price, it was almost worth buying them just for the battery holder, but an ancient grey-beard like me really needed a couple for their intended purpose …to light the way to the toilet at 02:00. So I bought a small stock of them (not enough, as it turned out), ripped out all of the white LEDs and replaced them with a single, yellow one and added a CDS sensor on pin 9 of the BSS0001 chip to ensure that they only switch on at night. A couple of them have been sitting (out of kicking range) on the stairs for several years now and are worth their weight (without batteries) in gold.
Anyway, when the need came up for the warm-body-sensor, I immediately thought of the depleted stock of OLEBYs sitting in the drawer, still in their original packaging. As I mentioned above, I wanted the sensor to interface with an ESP01S, so that I could MQTT the heck out of any warm bodies that came into range in the middle of the night (I’m totally screwed if the intruder happens to be a zombie of course). The reason the OLEBY and ESP01S are such a good fit is that the sensor will be working in the middle of a field …and the bodies in question (zombies or not) may not always be human shaped. The field in question is outside of mains-extension-cable range, but is still fairly close to our house; close enough for an ESP to be able to piggy-back off our WiFi network. The idea is that the OLEBY will trigger as usual, but instead of turning on a bunch of LEDs, it’ll turn on the ESP8266 instead. The ESP will boot, latch the power switch on (as the OLEBY will time out if not re-triggered) and then quietly send an alert message to our MQTT server, which we can then act upon depending upon how close to harvest time it is (lights, noises, hand grenades, dynamite or 200W rendition of Slade’s “Merry Christmas” …no, you’re right, that last one is probably banned by the Geneva convention).
So, poking about in the (fairly manky) guts of a dismembered OLEBY (don’t they have any de-fluxing solution in the middle kingdom?) trying to find where the trace from pin-2 went before it hits the LED switching transistor/FET, I discovered something interesting. The brand-new batteries I’d just slotted into the thing measured a pretty reasonable 4.83 volts …but the output from pin-2 measured 5.1v. Eh?!?
In all of the times I’d had the backs off these things, I’d never really looked closely at anything very much beyond the BSS0001 chip or the LEDs, but it seemed like there was something quite interesting going on here. There’s no mention of a charge-pump in the BSS0001 datasheet, so what was happening?
The answer appears to be in that clump of components across at the left-hand side of the board, away from the sensitive BSS0001, where an electrolytic capacitor sits on the reverse (LED) side of the PCB. Something needs a little bit of smoothing (first clue). Now that I get the magnifier out, I can see that a three-pinned device which I’d assumed was a transistor driver for the LEDs is actually labelled as “U1” (second clue). And there, hidden in plain view right next to U1, are a fairly chunky diode and another component labelled as “L1”. Well, who’d have guessed it …the humble (and don’t forget cheap) OLEBY has a fixed-voltage, boost regulator inside it. No wonder the things never seem to lose any sensing range, no matter how dead the batteries get.
U1 is something of an enigma. There are no particularly legible markings (“E502”?) on the chip itself and, until today, I would have been willing to bet that there was no such beast as a three-pin boost regulator chip. To begin with, I was working on the assumption that it was probably a transistor being driven by a clock signal from the BSS0001. However, a Gewgull search first turned up the ON Semi NCP1402, five-pin, micropower regulator, where one pin is marked as “NC” (no connection …hah, maybe the “NCP” part of the NCP1402 stands for Non-Connected-Pins!) and yet another, the chip-enable pin, can be permanently tied to the output pin, so we have at least a theoretical three-pin boost regulator after all. A little more searching through supplier product listings produced a couple of entries for SOT23-3 devices, like the TI TPS613222. So there is such a thing as a three-pin, SMD, boost regulator chip after all. Not only that, but the link to the TI datasheet above will open at an example circuit which seems to be a perfect match for the OLEBY layout (although the actual pin assignments for the TPS613222 don’t match U1).
I’ve just checked the on-line IKEA catalogue for the OLEBY sensor light and, here in Japan anyway, they still have them in stock (although the colours seem to be limited to black, white and red …and the price seems to have gone up, too), but it may still be worthwhile picking up a few the next time you’re in your local store buying some kitchen cabinets, coz’ now you know you’ll be getting a handy-dandy, micropower regulator for your battery-driven projects as part of the deal (oh, and lots of extra flux, too).
If the non-zombie detector ever gets to the decent working prototype stage, I’ll publish another article with the details and link to it from this page (but don’t hold your breath).