Sense 120VAC

[ronsimpson]

I like the resistors the way you did it. People think "120 VAC" and "GND" will all wise be that way. I find that "line" and "neutral" get switched around. This way if and when your meter or scope probe shorts out you are some what isolated from the power line, both sides.

With the 4 diodes (not one) the current into OK1 is most of the time. (not 45%) So the capacitor needs to work only about 10% of the time.
On the output the time constant is R3 C1.
On the input the R is complicated. It is the impedance of OK1 LED.
If I was making a PCB I would make a place for two caps. But probably only use one.

 

[Externet]

Could you suggest a pair of specific parts?

Any neon bulb superglued to a LDR or phototransistor in black shrink tube will do it.

I drew the schematic for my probe and it is not that simple. Two opamps.

Here is another way for the sniffer probe:

 

[Pommie]

Just play with the opto and then sort out any short comings.

No need for anything radical that involves superglue.

Mike.

 

[KeepItSimpleStupid]

You really want to use a reactive suppy to avoid resistor power dissipation.

There are ICs that can also do bbetter detection.

 

[jack0987]

You really want to use a reactive suppy to avoid resistor power dissipation.

There are ICs that can also do bbetter detection.

Please tell me more.

 

[jack0987]

I like the idea of the neon bulb and phototransistor set up for two reasons:
1. No filtering of the line with a bridge, cap and resistors
2. Possibly less danger of a lightning strike damaging the gear.

Using a 110VAC neon bulb for light on the LDR, I have come up with two designs that may work well with some minor modification. Please see following images.

There seem to be many types of LDR.
What specific part may work well with these designs?
Here are some possibilities (https://www.allelectronics.com/category/467/photocells/photoresistors/1.html).

I do not have any BC547. How about 2n3904 instead?

 

[jack0987]

Here is another way for the sniffer probe:

This is very interesting using a copper strip.
Is the copper strip used as a light detector or in another way?

 

[ronsimpson]

Is the copper strip used as a

Probably the copper strip and the wire makes a capacitor. (very small) AC on the wire will cause a small amount of current in the base of the transistor.

 

[KeepItSimpleStupid]

See fig #2 and Fig #4 here: https://electronics.stackexchange.com/questions/92517/how-to-drive-a-led-strip-from-ac-power-supply

 

[jack0987]

See fig #2 and Fig #4 here: https://electronics.stackexchange.com/questions/92517/how-to-drive-a-led-strip-from-ac-power-supply

Thank You.

 

[AnalogKid]

If this went by in the thread, I missed it: How quickly do you need to know that AC is on, and how quickly do you need to know that AC is off?

ak

 

[jack0987]

If this went by in the thread, I missed it: How quickly do you need to know that AC is on, and how quickly do you need to know that AC is off?

ak

For me, within a second or two would be good enough.

 

[eTech]

Hi

I used this on an AC lamp driver board. You could use the same approach as an input to a micro-controller.

eT