Computing stuff tied to the physical world

TD – KAKU remote switch

In Hardware on Mar 13, 2012 at 00:01

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:

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

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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:

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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:

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

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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:

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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!

  1. You are correct on the overheating protection although it’s not a PTC. It’s actually a thermal cutoff fuse. These components can either be on or off where a PTC can be in an analog state between R0 and Rmax.

    The first two pictures in your post indicate that the units contain one of those. The third symbol from the left in the first picture is a symbol used for these components.

  2. I wonder if the first symbol from the left (CE mark) had something to do with the inclusion of the thermal fuse?

    • That is correct, without the thermal fuse they would not have received the CE mark! The thermal fuse is in there to reduce the chance of fire if the unit is overloaded or shortcycled. The relay contacts are the weak point of the system and will overheat first. If the unit were to shortcycle the contacts heat up and the fuse would cut off the load at 130 deg C, below the flash point of the plastic. It must be in series with only the control mains as it is only rated for 2 A, if it were in series with the mains going back out to the recepticle it would trip with 5 amps through it.

  3. There is no sign of a resonator or crystal; would that explain the sometimes flakey behavior? One of those units I own is particularly annoying in that it doesn’t switch by the remote control; an RFX unit picks up the signal, the home automation kicks in and re-transmits the command through the RFX, which eventually leads to the unit doing what it is supposed to be doing in the first place: switch. Tuning the coil might be an option?

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