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

Today’s episode is about the “KlikAanKlikUit” remotely controlled AC mains switches, a.k.a. KAKU.

I’m going to look at two different units, the older/smaller/cheaper PAR-1000 supporting 16 different addresses, and the newer YC-3500 supporting up to 256 different addresses and switching up to 3500W:

Here’s the PAR-1000, once opened (you need a TX9 torque screwdriver for both units):

There’s a .22 µF X2 cap as transformer-less power supply, in series with a 100 Ω resistor (hidden in black heat shrink tubing, bottom right, next to it). According to this calculator, you can get up to 12.2 mA out of that, when using a bridge rectifier (which is under the cap, using discrete 1N4007 diodes).

The measured power consumption is 0.58 W. Note that due to the way these transformer-less power supplies work, this power is always consumed, whether the relay is turned on or not.

There’s an interesting post-production “mod” in this unit, on the relay, i.e. top middle in the above image. After removing the tiewrap and glue, this interesting part emerges – in series with AC mains:

I’m guessing some sort of overheating protection for the relay, a PTC resistor?

Here’s the copper-side of the PAR-1000’s PCB, with what looks like lots of solder flux residue:

And here’s the YC-3500, in a slightly larger enclosure and using a relay which can switch up to 16A:

Same 100 Ω resistor but beefier 0.33 µF X2 cap, bringing the maximum current to 18.2 mA. Measured power consumption is 0.81 W – what a waste for an always-on device which is merely switching another device!

Here’s the underside of the YC-3500’s PCB:

Both single-sided non-epoxy PCB’s have SMD’s on one side and through-hole parts on the other, but the amount of solder on the SMD side suggests to me that everything has either been soldered on by hand or glued on and wave-soldered. The extra solder on the left increases the PCB’s current carrying capacity, BTW.

These 433 MHz units respond to simple packets using the On-Off-Keying (OOK) protocol. There’s no way to control them directly, other than via RF – and even if there were, there would be no way for a home automation system to know their state since these units are receive-only. The relay is off after power loss. There’s an LED to indicate the actual on/off state. The choice of 24V relays is wise – needs much less current than 5V and 12V ones.

Note the 433 MHz antenna – a single loop of copper wire in one case, and a loop plus coil in the other!