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Illuminated Push Buttons

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Do you have a link to your illuminated PB switch specifications?
From the specs, his lamp was a bare LED, so he needed the diode to convert AC to pulsating DC, and the resistor to limit the current the the LED.

Ken
 
So it's an LED, setup with an internal resistor for 24VDC. If your intent is to power it from 120Vac, you will need the diode and a 10K-1W resistor. Remember that the resistor will be dissipating 1/2W of power as heat.

Ken
 
Hi,

I agree with Ken in that the resistor will dissipate almost 1/2 watt which means it might get a little hot.
You might also want to use a diode in reverse across the LED connections to protect against reverse surges.

However, there are other ways to drive an LED from the AC line. One of these ways is to use a capacitor and resistor instead of just
the resistor. The capacitor limits the current without the power loss of a single resistor so nothing gets hot.
If you are interested i'll post details or a link.
 
Hi,

Here's a quick circuit. Some other circuits use a full wave rectifier for a little more brightness. That's also possible.
 
Thank you Al for the nice schematic but my knowledge in electronics is very limited.

Starting from the left on your schematic we got the 120VAC black wire going to a 0.5 capacitor and thru a resistor then there is a line with a diode which goes where?

Then there is another diode and a line with a 100u capacitor and this line is going where?

I will assume that one of the lines in question is the white wire for the 120VAC load and the other line must be for the LED but not sure

Is it possible to mark your schematic what each line is for?

Thanks
 
Hi,

You mean the ground symbols? Those dual lines with a line leading to them are what is called a ground. That's not really earth ground though, just a common connection so all those parts with the ground symbol connect to the white wire of the line, and the black wire of the line goes to the capacitor on the left side. The capacitor is 0.5 microfarad that's what the little 'u' means: microfarad.

If this still isnt clear i'll draw some more lines.
 
No need to draw a new one Al, thanks anyway

I know about the ground symbol but what I mean is to clarify just the vertical lines on your schematic. So starting from the left we have the 120VAC line coming in, then the 2nd vertical line I guess represents the return line to load to complete the on/off switch function.

Then the 3rd and 4th vertical lines must be the connection to the switch

Is this correct?
 
oskar270 said:
No need to draw a new one Al, thanks anyway

I know about the ground symbol but what I mean is to clarify just the vertical lines on your schematic. So starting from the left we have the 120VAC line coming in, then the 2nd vertical line I guess represents the return line to load to complete the on/off switch function.

Then the 3rd and 4th vertical lines must be the connection to the switch

Is this correct?
Click to expand...

Hi,

The dark 'arrowhead' looking symbols are diodes. The lead with the short thick line is the cathode, the side with the back of the arrowhead is the anode. There are two diodes in this circuit and they have to be rated for 400v or better (because of the line reversal and the cap voltage when it is charged up.)

THe "120vac" round circle with the squiggle in the center is the AC line voltage drawn as a source.
The line comes out of the top and then turns right, and then goes to a 'vertical line' and that is the left side of the capacitor. The lead connects to one leg of the capacitor. Then the right side of the capacitor is another short vertical line, and the lead coming out of that side connects to the resistor R1 on the left. R1 on the right then connects to a point (node) that connects both to the upper diode anode and the lower diode cathode. The lower diode anode goes to ground. The upper diode cathode goes to both the LED and to C2 the other cap if you use that other cap. It goes to the LED anode and the LED cathode goes to ground. The upper diode cathode also goes to the top of C2 which is a narrow horizontal line, and the other narrow horizontal line is the other plate of the capacitor and that connects to ground via it's other lead.
All the ground connections (there are a total of four of them, one being the white AC line) go to the 120vac white wire.

Just to recap the capacitor is a 0.5 microfarad capacitor and it must have a rating that is rated for AC line voltage operation. This means in the data sheet it will say "rated for constant AC line voltage" or something like that. It might not even have a DC rating like many caps do.
I think people also use ceramic caps for this purpose.

Just to note again, the resistor R1 should not get hot because it only has to dissipate on average about 110 milliwatts, which is less than half it's power rating.

You might also want to note that the connection for the 'other' diode (lower diode here) is not the same as when using a resistor alone because it has to conduct when the incoming line voltage goes negative. In a resistor only circuit that diode goes on the other side of the upper diode and conducts only when there is a surge of a relatively small current though the upper diode capacitance. No need to worry too much about that here as long as the circuit is wired as is.

As another small note, when the circuit is unplugged there is a chance that the cap C1 can stay charged up to 170v or so, so some people connect a 1 megohm resistor across that cap so that it discharges faster. You can do that too if you like but probably dont need it in this app because the circuit is probably not going to be unplugged.
 
Last edited:
panic mode said:
Oskar,
24V (DC/AC) and 120V (AC) buttons are very common. they are used everywhere. you can add contacts if you need.

for example check this out:
https://www.automationdirect.com/ad...lluminated_Pushbuttons_Flush_-a-_Extended/LED
Click to expand...

Thanks for the link but all push buttons there are momentary and I need latching push on/off. I have a very hard time to get the push buttons I want and spent so far $50.00 and still dont have what I want LOL. Looks like that most of the switches on eBay are momentary or are the small round ones and I wanted to have the large round ones (I think they are 24 or 27mm).

Finally I had to settle for the ones I describe on this post which are the small round ones and still have to do all this soldering with the resistors / diodes which I dont like. I will never understand why a large round latching push button with the light and at various voltage is so hard to find

Thanks for your time
 
I was thinking about them but my preference is the round latching ones.

Perhaps in the future I may go with this type

Thank you
 
Hi,

The right part for the job? How boring is that :)
 
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