Computing stuff tied to the physical world

TD – Solar light

In Hardware on Apr 24, 2012 at 00:01

Welcome to the Tuesday Teardown series, about looking inside the technology around us.

The other day, Ard Jonker pointed me to this item available at the Dutch Lidl stores for €12.95:

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A solar LED light you put in the floor outside, which automatically lights up when it gets dark.

It’s about 14 cm in diameter, and 6 cm deep – let’s have a look inside:

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A solar cell, with two white LEDs, held in place by two screws yearning to be removed:

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The red leads connect to an on/off switch which can be accessed from outside. The batteries are 800 mAh, according to the specs, and look like standard replaceable AAA cells. The PCB has a chip on the other side:

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Hey – not bad, two NiCad NiMH’s and a little chip to drive the LEDs. This could easily accommodate a JNµ!

The DIP-8 chip in there seems to have logic for turning the LEDs on only when it’s dark (weak solar cell voltage, I assume). It does a bit more though, as this scope trace of one of the LED shows:


Probably some sort of charge-pumping, to drive the LEDs beyond the 2.5V supplied by the batteries. The power consumption is about 9.5 mA, so these lights should last through the night if there is enough sunlight during the day to fully recharge the batteries.

Neat. This could make an excellent power source plus enclosure for a JeeNode Micro, but note that the big metal ring is essential – it presses the glass and rubber seal tight against the rest of the enclosure “cups”.

  1. Ugh, they still sell NiCads? I thought they were all NiMH by now. So bad for the environment, most people will just chuck these lights in the trash when they don’t want them anymore…

  2. The 3rd picture is not visible. I am not sure is it just me or there is something you could fix at your end. – this link seems broken.

  3. I’ve made a similar “power supply” with a solar light. I’m using it to supply a jeenode (weather station with an sht11).

    I draw a graph of Ni-mH cells here (yellow trace) :

    It works nice since a year now although lake a sun , for 2 or 3 weeks -> raining and raining :-(

    The PCB in the solar light was an oscillator to supply the led with a pulsed current (modulated by an LDR light-dependent resistor). I have removed that function and just kept the diode (between the solar cell and accus)

  4. Looks almost like the one I’m working one. It’s easily able to power one LuxPlug reading per minute and one RFM12b transmit every 5minutes. Even with some cloudy days the batteries stay fully charged through the night:

    Some more details about my solar light:

  5. Have you found out anything about the chip?

    From the functionality I first thought it might be a PR4403 (, which is designed for exactly this use case, but the PR’s switching frequency is five times higher than what you’ve measured, and it would only need a single cell.

    BTW, are the two cells connected in series or parallel?

    BTW2, I’ve been using the PR4403’s little brother PR4401 in SOT-23 package to power a single white LED from AAA cells that had been declared empty by the devices they were used in before. Each of the cells ran the LED for several nights, before it was really empty.

    • Added a picture – the chip is marked “5253” and “1101” (1st week 2011). Batteries are in series.

  6. It’s certainly a boost convertor chip (the clue is the silkscreen marking L1) but I fail to find a reference to 5253. Perhaps a shot of the underside would clarify the pinouts?

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