First stab with my DSO Quad – 12v dimmer experiments

In our living room we have some ikea cable lights and we replaced their transformer based driver with a switching one.. I forget what model it is but it looks a lot like a laptop power brick. Anyways, we’ve had it for years, but i always got the feeling that it wasn’t as bright as it should be.

I just got a Digital storage oscilliscope, so I decided to take a look and see what the deal was.

In this case i knew the RMS voltage is 12v, which is a peak-to-peak voltage of around 35v. I checked, and my scope can handle up to 80v.

There are 2 main components to the lighting system:
* wall dimmer, which is an insteon 6 button keypad
* 12v driver, which is up in the attic and takes the 120v from the switch and drives 12v to the lights.

I am pretty sure the wall dimmer is the kind that chops the AC waveform at the leading edge, so i expected to see the waveform in the scope be sort of a truncated SIN wave.

What i saw when i started was a truncated sin wave, but it also itself was made up of a nice sin wave. That must be a function of the 12v controller. Curious indeed.

As i increased the brightness, the overall sin shape returned almost all the way, but the sub-wave remained. The main sin wave never became fully ‘on’.. I think this is caused by the wall-dimmer i have.

check out the traces:

The last trace is zoomed in more than the previous 3.


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