Cheap but useful device, simple case…cracked easily
…It started when I needed for a cheap device that can light up parts of home when it’s dark automatically detecting presence and turning off in some time.
Found pretty slick device cheaply on Ali. Seems lot is still alive:
Device arrived in few weeks. Exactly as advertised.
Left bottom — ambient light sensing photo-resistor.
Upper right — omnidirectional PIR sensor
Pretty bright white LED — right in the center, surrounded by the reflector.
The only problem - lighting period was about 30 seconds. I wanted more. So the investigation started.
We see same sensors, key transistors to light up the LED, two current shunt resistors and the rudimentary brain of the whole device — BISS0001 IC.
Finding datasheet was an easy task. Few moments later I’ve got a URL and started to read:
So yes, PIR motion detector, some features and capabilities described. But I need to understand how timings work for that little thing.
Spent some time using oscilloscope probing IC pins, found that Pin 2 (V0) is low when LED is turned off and high when it’s on. No discharge typical for RC’s so it’s already trigger output. Ok, let’s see what’s related to that in datasheet.
Bingo, here it is:
Pin 2 is detector output with active high, indeed. And timing for keeping light on can be set using:
I need only Tx. Don’t care about Ti.
Now let’s find reference schematic:
Same formula: Tx=24576 x R10 x C6 found. Now need to find matching to R10 and C6 components on a PCB I have.
R2 on PCB is R10 on reference schematic.
C1 on PCB is C6.
C1- 10n (0.01uF)
Putting values into formula — ~29.5 seconds (didn’t try to make it in right UOM scale and it doesn’t matter)
So yes. This is timing RC chain. Since I’ve already had 39.9n capacitors in 0805 case — few seconds later and with the help of my precious in all senses JBC (DDE series with PA120-A microtweezers) soldering station…
…capacitor replaced (from 10n to 39.9n).
Now assembling the device back, testing — now it emits light exactly 4 times longer.
Hope you’ve enjoyed device price and practicality and how simple is to tune it up for your needs.