PIR motion sensing LED light

This LED light was purchased in late 2014 in a supermarket. It is battery-supplied, and comprises a passive-infrared (PIR) motion sensor, so that it lights up only when somebody passes next to it.

PIR motion sensing LED ligth

The bottom of the light provides access to the battery holders. The number of batteries is surprising: 8xAAA dry cells are needed, in two sections. Batteries were included. Turns out, while the cells within a section are connected in series as usually - providing cca 6V supply voltage - the two sections are in parallel (connected through diodes, so should one section contain discharged batteries, the diodes prevents them from loading the other section with fresh batteries). The probable reason for this solution was to provide a similar lifetime as the other similar product, which was sold at the same time, and had half the number of LEDs.

PIR motion sensing LED ligth

In between the two battery holding sections, there is a removable plastic holder plate, which could be wall-mounted using standard screws (not included) or a double-sided tape (included). The lamp then can be snapped on the holder, and removed when batteries need replacing.

PIR motion sensing LED ligth

After removing the top cover, a metalized plastic layer is revealed, which serves as a reflector for the LEDs, enhancing the light output in the desired direction.

PIR motion sensing LED ligth

Below that, the PCB is visible, where the LEDs (E), the PIR sensor (C) (which had an opaque platic cap (A) fitted on its top, to widen its "viewing angle") and an ambient light sensor (phototransistor) (D) is mounted. Two bulky electrolytic capacitors (B) which did not fit on the "SMD-side" of the PCB, are also visible here.

PIR motion sensing LED ligth

The PCB is single-sided, as is the norm in this sort of products, and as it is adequate enough to provide all the needed interconnections. There are no high frequency, low-level signals, nor high power lines in this circuit.

schematics of PIR motion sensing LED ligth

The circuitry is not that different from an older-generation generic PIR sensor/light. The major difference here is the usage of a dedicated integrated circuit instead of generic op-amps, providing both the analog amplification and the subsequent timing.


This is a nice example of a product with well balanced cost-to-utility ratio. Using a higher level of integration helps to cut the cost down to the bones. As a consequence of the fact that this kind of products is produced exclusively in Asia these days, the related integrated circuits (and their documentation) are mostly unavailable in the "western" world.


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