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Wiring a Switch (yes I’m embarrassed)  


Notace
(@notace)
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Total noob here. I was a programmer in my working life (now happily retired) but have little or no electronics knowledge. But I can follow instructions. I’m building an ATX power supply following your YouTube video. I intend to use it to provide accessory power for the model railroad I’m building. I’ve breadboarded the project and got it working OK. I’m going to 3D print an enclosure which I’ll attach to the power supply. 

I’ve decided I want a rocker switch for power and ideally I’d like to use an illuminated switch. I’m embarrassed to ask this but how do I wire this up so the switch illuminates when the circuit is on. This would be instead of using the power LED in your design. The terminals are just marked 1, 2 and 3 but I’m not sure what to connect to what.

Please excuse the noob question, and thanks for your videos. 


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Pugwash
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I am no electrician but it is time to get the multimeter out.

I have some KDC1-201 switches lying around and I haven't got the to light up either. After reading your post I thought it is time to get them out again. Not sure whether I had been duped and that they don't light up, I did a BigClive on one. Once I got one apart I was expecting an LED and resistor but found a small filament bulb.

I hadn't been duped!

You need to measure the resistance between the various pins, where you find virtually zero resistance, this is the route of the power line.

Assume pins 1-2 = 0Ω, 2-3 = 40Ω and 3-1 = 40Ω. My guess is that the middle pin will be connected to the rated voltage, so if you connect pin 1 to ground you will short the circuit but connecting 2 - 3 will light up the switch when on. Might help if you have a bench power supply to start at a low voltage and slowly increase to the rated voltage.

Sorry, I can't be of more help, but it is unlikely you will kill yourself at these low voltages, but you may end up sacrificing a switch.


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Notace
(@notace)
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Hi Pugwash.

Thanks for the reply. In this application, the switch doesn’t really connect the power. It just connects the green wire to ground, which tells the power supply to “turn on”, so no real load goes through that circuit. 

My (very limited) understanding of these switches is that the load is directed through the switch and that some of that voltage is used to power the lamp. Of course, it’s very possible that I’ve got that completely wrong.

Ron


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Pugwash
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Update:

Five minutes later I got my switch to light up!

Thanks for making me think about the problem and there is certainly no need to be embarrassed. My father was a mathematical genius and after he retired, he studied with the Open University and attained a Master's Degree but he couldn't put a shelf on a wall that stayed up for very long. ? 


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Pugwash
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