Issues with Touch Sensitive (On/Off) Lamps

Quick article on a seemingly simple problem that took weeks of dabbling and researching before I was able to resolve this problem.

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Word of Caution:  This involves working with electricity.  Before attempting any such work, unplug the power cord to the bulb and/or turn off the breaker to the outlet you’re working with.

Touch on/off lamps were all the rage years ago when the idea of body capacitance to control fixtures was introduced. This is the fact that your body can act as a capacitor and allow a simple switch to vary the brightness of a bulb or to turn it off/on.  This capacitance forms the foundation of the instrument called a Theremin which makes the spooky “woo woo” sounds in the Beach Boys’ song Good Vibrations.

Touch sensitive lamps are simply lamps with an add-on “box” that detects when you touch a common wire and it then varies the brightness of a bulb from off, to usually three levels of brightness and then back to off again.  This wire is must be connected to a metal object, often the base of a lamp or the hinges on a curio cabinet.

The problem I was experiencing was related to a curio cabinet that used the hinges to provide contact from your body to the touch sensitive features.  I became aware of this issue while installing Apple Home Kit devices, in my case using Phllips Hue Light Bulbs (I have a forthcoming article on my experiences setting up HomeKit with such devices).

In any case, what I found is that the Hue lightbulb in my cabinet would simply switch off after a matter of time.  For this light bulb, I had to set the brightness to the max (three consecutive touches) because at the lowest level there was simply not enough power to for the circuitry in the bulb, and it would flash to warn me of this condition.   After programming the light and linking to the other cabinet light (which had no issues) it would simply turn off after a few minutes.

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Capacitive Touch Light Control Diagram

After some research I concluded that the actual light control box (labeled TP-01 in the diagram) must have been damaged from a power surge (which is common).  So I ordered a replacement device (a Westek Replacement Kit Touch Dimmer – $10.24 from Amazon and installed it.  The installation was relatively simple.

I switched on the lamp by touching the hinge and then blip, it went off just like before.

Skip this next two paragraphs if you’re not interested in the things I tried before I stumbled on to the solution.

Okay, so then I surmised there may be an issue with my Hue bulb.  I swapped out the bulb and blip, it went off.  Alright, so maybe it’s an issue with HomeKit bulbs in general, so I put in a 40-watt incandescent bulb and, blip, it went off as well.  Sooo… I re-read the instructions and noted they indicated that the large-prong wire from the wall had to go to a specific wire on the box.  I used my trusty voltmeter and followed the large prong wire to the dimmer box and yes, it had been swapped be me.  I swapped it back to the correct configuration, turned on the bulb and blip, it went off.

Great… so then I disconnected the touch portion of the box and turned on the bulb manually and…it stayed on!  Hmmm…  I checked the other cabinet, where there was no issue, and removed the hinge on that cabinet to make sure there wasn’t something I had missed in the wiring of the capacitor wire to the hinge.  There wasn’t.   I then followed the working-cabinet-light wire to the wall and found that it plugged right into the outlet.  I followed the non-working cabinet wire and it plugged into…an outlet multiplier!  I then moved the plug into a direct connection to the outlet.

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A typical outlet multiplier.  Not the one I have.  Also known as a power strip, for larger adaptations.

I had discovered the root cause of the issue! Apparently, plugging the capacitive (dimming) light into an outlet multiplier relies on the wiring in the multiplier to correctly convey the ground signal.  In my case, this outlet multiplier was apparently not doing its job.   Perhaps it was damaged, or perhaps a more rugged version might work properly.  After switching the cabinet lamp to a direct connection to the wall, the light has remained on ever since.  In fact, I’ve not been able to turn it off.  That last sentence is not exactly true.

So at least I have a new capacitive touch box on my left cabinet light, quite a brag I must say!  But I could have saved $10 and a lot of hassle by simply moving the plug.

Hope this helps anyone with a similar problem.  If you discover other oddities about this setup, please comment below!

 

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