Battery LED PIR Lights

[Jimk]

Does it matter? At a fiver each is anyone really going to make their own?

[Jimk]

Ahh... gotcha! :-)

[Dave Liquorice]

Having seen the thread about how useful battery powered LED PIR lights where during a power cut decided that a couple would be useful here. Fosicked about on Amazon, reviews variable. Wish Listed a few options at about a tenner for three exc AAA batteries.

Shopping in Aldi, Hexham on Friday spotted their "Lightway", 15 LED SMD, 120 lm, PIR, battery lights at £4.99 each inc 3 x AA batteries. Bought a couple. Trying out they are very bright, spots before the eyes bright, too bright for a "see where you're going" light during a power cut. They would also come on when the room lights where on, so a fairly high light level.

Opened one up (4 small screws) traced out circuit. All 15 LEDs are in parallel fed via a single 2R4 resistor. SPDT switch connects battery

-ve either to this resistor (for ON) or the source of a FET, the drain goes to the resistor (for AUTO). The FETs gate is connected to pin 5 of an unmarked 8 pin chip. Ambient light level detection is a photodiode in series with a 820K resistor across a 3.3 V regulated supply. The juction between photodiode and 820K resistor is high with the photodiode illuminated and falls with light level and is connected to pin 6 of the chip. A PIR module is across the 3.3 V supply and its output goes to pin 7 of the chip. PIR module output goes high for about a second when it detects movement. Pins 4 and 8 of the chip are connected to -ve. Pin 1 +3.3 V. Pins 2 and 3 don't appear to be connected to anything either visually or trying continuity from them to elsewhere on the board.

Two simple mods bring the brightness down and make the "dark level" lower. Brightness is just replacing the 2R4 with something higher. I used 100R, might be a bit too big but still enough light to see by and with AA rather than AAA batteries they should last a very long time. "Dark level" I swapped the 820K for 1M, they no longer come on when the room lights are on.

Slight niggle is that the photodiode is partly shaded by the plastic tunnel for one of the LEDs so ambient light sensitivity is directional. Light sensitivity is also very quick to react. At lowish ambient light level waving an arm/hand nearby but not shadowing the photodiode the light doesn't switch on. Let the arm/hand shadow pass quickly over the photodiode and it does. I guess a small capacitor across the 1M resistor would slow the response down if this becomes an annoyance.

[newshound]

Excellent, a real DIY post!

[Graham.]

Agreed.

Who needs to sit a 20min Big Clive teardown, when you've got a quality write-up like this?

[Brian Gaff (Sofa)]

This sounds a bit like an led version of some Altai models I used to have that used torch bulbs, which meant battery life and brightness were none too good back in the day. Brian

[Dave W]

From such a detailed description I drew the circuit, but I have some queries.

What chip provides the stabilised 3.3V?

I can't find anything about how long the light stays on when triggered, but a similar one by Amtech says 20 minutes. So presumably the unmarked chip contains a digital timer, but there must be a capacitor associated with that. So what other components are visible?

I looked for a timer IC but did not find one with appropriate pins. The 555 timer has -Vcc on pin 1 and +Vcc on pin 8, the opposite of yours, so I'm wondering if you are counting pins in the wrong direction?

[Dave Liquorice]

An unmentioned LDO 3.3 V SMD regulator marked 662K with decoupling capacitor between output and GND.

Only other things I didn't mention is a 10 K to GND from pin 5 (drive to the FET) and a 0 ohm resistor in the battery supply to the regulator, presumably to get the singled sided board layout to work. I've also tried to track down what the chip is without success. The on time is about 15 seconds. Neither of the resistor changes has altered that. The only capacitor is the decoupling one for the regulator.

Pin 1 is by the dot or other mark isn't it? B-)

[spuorgelgoog]

Usually, but that wouldn't stop the Chinese making use of a run of chips that went backwards into the marking machine.

Owain

[Dave Liquorice]

Hum, the mark is moulded hollow rather than a blob if ink.

Having had another look for any sort of chip that even vaguely matches the traced out connections (GND, +ve) and rescuing the intial layout sketch from the bin (with components in the orientation they are on the board and position). Pin 1 is +ve and 4 & 8 gnd. Almost everything I've loooked at has pins 4/8, gnd/+ve.

I've looked at D flip-flops, J-K flip-flops, watchdog timers, programable supervisors, op amps. A PIC12F683 sort of fits has +v, gnd, comparator inputs and an output on the correct pins, internal oscillator but seems over kill and expensive for a device selling at £4.99...

[Dave W]

RS Components sells it for £1.10! If it is a microcontroller then theoretically you could reprogram it to anything you want.

[Dave W]

Yes. The 662K on the regulator equates to the Torex XC6206 3.3V ±2%

200mA max o/p. If it's that accurate I would guess that it could well be supplying a microcontroller. You say that the latter is unmarked, but I've seen marking that is only apparent when the light source and your eye both make the same angle to the surface, as if it was a mirror.

[Dave Liquorice]

Microcontroller still seems over the top and expensive even at £1, that's a fifth of the total selling cost. Most retail markups are

100% or more so cost price has to be down at £2.50 or lower...

I looked at various angles of both light source and eye with a magnifying glass not hint of any markings. No sign of them being ground off either.

[Dave W]

What about black paint which might be removable?

[Dave Liquorice]

Here, have this straw. B-)

Probably not but if it is a microcontroller one assumes that the comparator switching point and light on time are variables or hard coded. *If* one could extract the code, patch it and reload...

"out of the box" these Aldi lights are very bright, perhaps if the microcontroller has an analoge out the switching FET could be not driven fully on/off, though the manual on would still be full brightness. The level of light that it considers "dark" is rather highand the on time on the short side. This is when using them as a power outage "emergency light" rather than their intended purpose of a cupboard or night time "see to pee" light. There is also the issue of the fast "dark" response and a passing shadow triggering them.

[Dave W]

It would be a bit hit-and-miss to try and half-switch the FET on. The microcontroller could output a variable on/off mark/space ratio to do dimming.