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I want to build a bathroom mirror frame with integrated LED spot lights. Current comes out of the wall, there are already two on/off switches which control that single outlet. That is why I „believe“ I cannot simply replace (one of) the switches with a turn knob dimmer.

The frame is only 2cm thick where I want to place the knob for dimming. The knob itself does not need to provide on/off functionality, only control the dimming.

The lamps have more room and there would be room for a separate trafo. I have not purchased any electronics, yet, so I would be flexible.

To my surprise I have difficulty searching the net for setups like this, including this site. It sounds simple, but all parts I find are much too thick or it is unclear whether I could use them.

Can someone recommend a part that I can use for the knob and the electronics that follow that decision? (dimmer with input for that knob, plus LEDs) Most LED Spots I find have the driver already included and then just claim to be dimmable. They are either for 12V or 220V, but I don‘t care.

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closed as off-topic by winny, Michel Keijzers, Voltage Spike, Finbarr, Harry Svensson Apr 23 '18 at 18:59

This question appears to be off-topic. The users who voted to close gave this specific reason:

If this question can be reworded to fit the rules in the help center, please edit the question.

  • \$\begingroup\$ Seeing as you changed it to a shopping request, this makes it now off topic for this site unfortunately. To make it on topic, you could maybe change the question to say what you are confused about when choosing a device (what specs to look out for etc) and ask what considerations should be made? \$\endgroup\$ – MCG Apr 17 '18 at 10:46
  • \$\begingroup\$ Thanks for helping me change the question to be on-topic. \$\endgroup\$ – stippi Apr 17 '18 at 11:01
  • \$\begingroup\$ The wording in my last paragraph is a bit unfortunate. I should have asked "Can someone recommend what sort of device I should use to implement the knob..." I did think of a potentiometer, but didn't know if that would work and how. That's why I marked the answer below as helpful, since it contains just the info that I need to go further. \$\endgroup\$ – stippi Apr 18 '18 at 13:33
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Last time I needed to adjust the brightness of a LED lamp, I opened up the device to access the driver PCB, identified the main constant-current driver IC, looked up it's data sheet, then desoldered the sense resistors it used to set the LED current and replaced them with a suitable value - I could have replaced them with wires to a potentiometer with an appropriate resistance range and located the potentiometer somewhere useful.

In my case the device PCB looked like this:

light PCB

I traced the circuit schematic from the PCB:

schematic

simulate this circuit – Schematic created using CircuitLab

The sense resistors are "R3" and "R4".

"U1" is a SM2082D constant-current driver IC, It's data sheet tells you what resistance values to use to set the current and hence the brightness.

A 15 ohm resistor in series with a 200 ohm potentiometer would have done the job.

potentiometer

You could make the same sort of investigation and find out if a similar change to the circuit would achieve what you want. Any electronics component distributor (Farnell, Mouser, etc) will have an online catalogue where you can find a suitable potentiometer for your needs.


If you don't want to do electronics design and just want to know how to wire-up a specific make and model of 120 VAC dimmer to a three-way switch setup for a specific make and model of light fitting, that would be a question for diy.stackexchange.com. Note that they also don't do shopping advice (what make and model product should I buy, from where) for the usual reasons.

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  • \$\begingroup\$ Thanks, this is useful info. Does that imply I need to use LED spots that don‘t have an in-built driver but instead a single external driver? \$\endgroup\$ – stippi Apr 17 '18 at 11:11
  • \$\begingroup\$ @stippi, It is a lot easier to modify the DC side of a separate external driver than to modify the circuitry inside an Edison-style LED light-bulb. The appropriate method depends on what LED lights you use, you might select LED strips based on the amenability of their driver circuit to this sort of change or based in their in-built dimming. Lots of different ways to do this. \$\endgroup\$ – RedGrittyBrick Apr 17 '18 at 11:27

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