Introduction: the problem
I really like the IKEA MOLGAN led light, a cheap (~6 Eurodollars) 3xAAA battery powered motion activated night light. I have a bunch of these, basically to illuminate from the bedroom all the way to downstairs.
However, it's a classic example of good idea, lousy execution:
- 1. It devours batteries; dead after 3 weeks. measured current: 112mA initially. This problem is exacerbated by a nighttime roaming feline insomniac.
- 2. Stays on for far too long: about 30 seconds. Way too long to get up out of bed and traverse the bedroom, hallway etc.
- 3. Emits cold creepy light from cheap white LEDs. This messes with my night time vision and easily wakes up my GF. Not...good...no waking up GF...no no no!
Clearly, some hacking is in order. We'll be replacing the LEDs with red ones, and adjust the timing to 10 seconds. Measured current after the hack was 74mA. All other things being equal, the battery lifetime will improve with a factor of (30s x 112mA)/(10s x 74mA) = 4.5, in other words, good for about 3 weeks x 4.5 or 3 months, without battery replacement. Acceptable. Empirically, this has been verified.
First off: you need to know how to hold a screwdriver and how to solder and unsolder SMD components. The usual tools are in order.
To perform the mod these parts are needed (per light):
- 5x 150 ohm 0805 resistor
- 5x high-efficiency red LEDs (5mm is ok)
- 1x 1M ohm 0805 resistor
- 1x 150k ohm 0805 resistor
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Step 1: Disassembly
To disassemble the light, first remove the batteries. Then prod (don't cut) with a box-cutter around the rim where the 'dome' top meets the bottom of the housing. It should open quite easily. Remove the two screws holding the PCB. Then melt the solder of one battery clip, while lifting that corner of the PCB upward. Repeat for the other corner and take the PCB out.
Step 2: Replace the White LEDs
Desolder the white LEDs by heating one end, then lifting the LED, then heating the other end. Unfortunately, I couldn't salvage them, as the plastic melted right away. Observe that IKEA was so kind as to put a '+' sign on the pad where the LED anode (usually the round side of 5mm LEDs) goes. I used regular 5mm reds from ali express. Clip the leads fairly short, as everything needs to fit under the plastic dome. If you can find or have SMD LEDs that fit, that's even better.
Step 3: Replace the Resistors
Replace 5 resistors (R12-R16) with 150ohm 0805.
Replace R2 with 1Mohm 0805 (Disaster struck as I was out of 1Mohms, so I put in 2x 470kohm in series).
Replace R11 with 150kohm.
Note that these values aren't really critical. If you want to change/adapt/calculate the timings, please read the datasheet of the BISS0001 chip that controls the thing. The circuit in the datasheet is practically identical to that of the MOLGAN light.
Step 4: Check, Reassemble and Enjoy!
Check with a power supply at 4.5V or battery in a holder that it works. Then reassemble the device. You might have to bend the LEDs sideways a bit, depending on how tight you clipped the leads. Insert batteries and enjoy your nightly excursions to the fridge without waking up the house or busting the bank for batteries!