Hello!
Is it possible to use a doorbell as a button but still have the 12V light still work?
Obviously, I have a 12VDC supply to use (also a 9VAC transformer).
Any questions/answers?
@anon44338819
Yes, a question. Is the light separate from the switch? Or is the light and the switch parallel so the light stays on, but dimmer, when you push the switch?
Why do you need to have the light?
The illuminated doorbell buttons have the lamp across the contacts. This is why on button press the lamp extinguishes. You would do better just to buy an illuminated button. A simple Google of "illuminated 12 volt button switch" will bring up dozens of examples.
Ron
[quote="Paul_KD7HB, post:2, topic:1026812]
Yes, a question. Is the light separate from the switch? Or is the light and the switch parallel so the light stays on, but dimmer, when you push the switch?
[/quote]
The light is parallel to the switch. When I press it, it goes dimmer.
It gives it more of a doorbell vibe 
Also, it's easier to see in the dark.
What's the point of buying a button when you can use what you already have (for now)?
And if you have a normal doorbell system, it is AC powered and uses a transformer to get the lower voltage. Beware, older homes have 24 volt doorbell transformers. Found out the hardway with the lights burning out after a week.
The point of buying a button is with the existing doorbeel button the lamp is in parallel with the switch, I am surprised it goes dim and does not extinguish when the button is pressed. These doorbells are designed to offer illuminition in poorly lit areas at night so a visitor can see the button. If the existing button will do what is wanted and meets expectations then by all means use it. However there are very nice illuminated buttons using LED and are inexpensive so if a better suited button can be found at a low cost then go with it.
Also, most older doorbells of this type used an AC transformer to reduce mains voltage (240 VAC or 120 VAC) to between about 8 to 16 VAC. The lamps were incandescent type. New illuminated buttons use LED and are not designed for AC.
Ron
LEDs work just fine on AC. As LEDs have a relatively low reverse breakdown voltage you would want to use them back to back to prevent destruction on 24 VAC. Select the current limit resistor based on the AC peak.
Leds connected to AC as you suggest will give a perceptible flicker
Not to my eye.
This is a red LED in parallel with a back biased 1N4148 and a series 2.2k resistor. It is driven by a 24VAC HVAC transformer.
Articles on the web alleging to show flicker don't take into account aliasing from the video camera. Most human eyes can't detect a 60Hz "flicker".
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I can't, been there and tried it. I can't even detect 50 Hz flicker. Really don't know what my "flicker threshold" actually is. 
Then too, a good many people claim they can notice or detect it at 50 & 60 Hz. Beats me.
Ron
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Terrible pun! 
Serialy though, film movies were shot at 24fps with barely discernible flicker.
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So if I power a LED with 50 or 60 Hz square wave and I use my DSLR camera to photograph it with my exposure set for 1/1000 sec the odds are 50/50 that while the LED always seems on to my eye I can catch it off or on.
Ron
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Only if there is a cat in the frame, Schrödinger.
I'm not sure what the odds would be but I'm confident you could catch it when it was off.
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Well figure with a square wave at 60 Hz it's on for 8.3 mSec and off for 8.3 mSec and at 50 Hz it's on for 10 mSec and off for 10 mSec so with each shutter release I should have 50/50 odds of on or off. That's my guess.
Ron
Are you triggering the shutter by hand? I can envision synchronizing pressing the shutter release so that, with practice, you could hit either state a majority of the time. Even though the cycle time is fast, you could develop a rhythm that would synchronize eventually.
My thought is based on photographing displays and catching them in all sorts of states. The 1/1000th shutter speed would make the results different than slower speeds but I'm not convinced it would be 50/50. on the other hand, I found my Probability and Statistics class in college pretty counterintuitive at times.
I'm looking more for a circuit.
I believe that a doorbell switch relies on the fact that the light + solenoid coil has a low enough impedance to permit it to pass sufficient current to light the light but not activate the solenoid. Your load might not satisfy this criteria. A lighted pushbutton as suggested in post #3 has a separate circuit for the light and may be more appropriate for your application.
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