Make signal lights for the AC outlet

[ningole]

Hello guys!
If this post is in the wrong place, please let me know and I will move it to the appropriate place or delete it.
I'm an electronics newbie and want to make an indicator light for an outlet but I'm not familiar with circuits, so I hope you can help!
My need is to make a 110/220V AC power indicator light:
AC power source -> A plug -> connected to 1 outlet.
On the outlet, choose 1 of 2 options:
1. Use 2 LEDs: 1 red and 1 green. The red LED corresponds to the left outlet pin, and the green LED corresponds to the right pin. If the hot wire is on the right pin, the green LED is on and the red LED is off. Conversely, if the hot wire is on the left, the green LED is off and the red LED is on.

2. Use only one 3-pin blue and red LED. If the hot wire is on the right, the LED should light up green. Conversely, if the hot wire is on the left, the LED should light up red.

I have read about ways to prevent reverse polarity, diode bridge, or using mosfet... but most of them are used for DC. With limited knowledge, I don't understand much.
So I would like to ask whether at least one of the above two options is feasible and if so, how can the circuit be designed? Hope you guys can help!
Thanks in advance!

 

[Tony Stewart]

You would be better off getting a cheap DVM than trying to build this idea, for a one time 1 second use.

 

[ningole]

You would be better off getting a cheap DVM than trying to build this idea, for a one time 1 second use.

Hi Tony, thanks for your response and your advice! This idea will be useful to me in some cases, and I'm only doing this in a single outlet. I think it would be better if I could find the position of the hot wire immediately instead of using a DVM, and I just need to know that.

 

[rjenkinsgb]

"Socket testers" are a common, standard item, eg.

https://www.aliexpress.com/item/1005004798480250.html

To run an LED from 120V or 240V AC, you can use a capacitive dropper. They use the AC impedance of a capacitor:
1 / (2 x PI x F x C)
in place of a high value, high power resistor

A 0.22uF capacitor has an impedance of around 12000 Ohm at 60 Hz.

That would give about 9mA at 110V, or 19mA at 230V

With a bridge rectifier that's the current the LED would get; with just a parallel reverse diode, it would average half of that.

You also add a relatively low value resistor to limit surge current for when the circuit is powered on.

It's a very common circuit principle, in things that can be totally insulated so there is no possibility of anyone touching the parts - they are live at lethal voltages!

The image below is an example I found on google, though I think they have calculated the current incorrectly.

You would need that twice, one for each LED.

Connect the resistor input to the live or neutral pin, and the lower connection to the ground pin.

Preferably use X or Y type capacitors, or one rated at least twice the maximum AC voltage, for reliability.

 

[alec_t]

Personally I would avoid the use here of any LED colour other than red, yellow or orange. Green is often used to indicate a 'go' or 'safe' condition, such as an Earth potential, so in my view is dangerously ambiguous for indicating the hot terminal.

 

[danadak]

Classic Neon bulb ?

See attached for applications.


Regards, Dana.

 

[Diver300]

Just use one of these:-https://uk.farnell.com/tenma/72-6861/test-outlet-socket-usa-plug/dp/8027080

 

[ningole]

"Socket testers" are a common, standard item, eg.

https://www.aliexpress.com/item/1005004798480250.html

To run an LED from 120V or 240V AC, you can use a capacitive dropper. They use the AC impedance of a capacitor:
1 / (2 x PI x F x C)
in place of a high value, high power resistor

A 0.22uF capacitor has an impedance of around 12000 Ohm at 60 Hz.

That would give about 9mA at 110V, or 19mA at 230V

With a bridge rectifier that's the current the LED would get; with just a parallel reverse diode, it would average half of that.

You also add a relatively low value resistor to limit surge current for when the circuit is powered on.

It's a very common circuit principle, in things that can be totally insulated so there is no possibility of anyone touching the parts - they are live at lethal voltages!

The image below is an example I found on google, though I think they have calculated the current incorrectly.

You would need that twice, one for each LED.

Connect the resistor input to the live or neutral pin, and the lower connection to the ground pin.

Preferably use X or Y type capacitors, or one rated at least twice the maximum AC voltage, for reliability.

Thank you for your very detailed reply, it includes calculated values for each component and safety conditions, I appreciated it!
Thank you for the socket testers, I will look it up!
I thought about using a bridge rectifier actually, but the point is when using a bridge rectifier, the direction of the current is always determined. Even if reversing the direction of the plug, the current behind the bridge rectifier always has a fixed direction, so I cannot determine when the LED should be on and when it should be off depending on the direction of the current from the AC source.
So correct me if I am misunderstanding something!

Personally I would avoid the use here of any LED colour other than red, yellow or orange. Green is often used to indicate a 'go' or 'safe' condition, such as an Earth potential, so in my view is dangerously ambiguous for indicating the hot terminal.

Totally agreed! However, I think it's for public use. This LED-stuff is used to integrate into a small electrical box, it acts as a small tester or measuring device. No one has the right to touch it except me, and I also use it infrequently. Therefore, I think it is acceptable in terms of safety.
Here's a picture of the box, it's not done yet and missing safety instructions, I'll add them later

 

[rjenkinsgb]

Even if reversing the direction of the plug, the current behind the bridge rectifier always has a fixed direction, so I cannot determine when the LED should be on and when it should be off depending on the direction of the current from the AC source.

AC = Alternating current; the polarity reverses twice during each AC cycle.

Correct or incorrect wiring changes which pins socket pins the voltage is between, not the "direction" of current; eg. if L and N are reversed, the N to E light will be on instead of the L to E light.

If there is no ground, both will light up regardless of L <> N being correct or not, unless you test with a separate ground to the Earth point in your tester to

 

[ningole]

AC = Alternating current; the polarity reverses twice during each AC cycle.

Correct or incorrect wiring changes which pins socket pins the voltage is between, not the "direction" of current; eg. if L and N are reversed, the N to E light will be on instead of the L to E light.

If there is no ground, both will light up regardless of L <> N being correct or not, unless you test with a separate ground to the Earth point in your tester to

Thank you for your response!
Oh my bad! It's the direction of the plug, not the "direction" of the AC current. Thank you for your explanation, I see now
I forgot the important point in your post, the Earth pin. So I understand that there will need to be 2 separate circuits for the 2 LEDs, one will be L-E, and E-N for the other. Unfortunately, grounding is not always available in my place. Even in my house, the electrical system does not have a ground wire so I must use RCBOs for safety.
So in my understanding, this idea's not possible without using ground wire, right?

 

[Nigel Goodwin]

Thank you for your response!
Oh my bad! It's the direction of the plug, not the "direction" of the AC current. Thank you for your explanation, I see now
I forgot the important point in your post, the Earth pin. So I understand that there will need to be 2 separate circuits for the 2 LEDs, one will be L-E, and E-N for the other. Unfortunately, grounding is not always available in my place. Even in my house, the electrical system does not have a ground wire so I must use RCBOs for safety.
So in my understanding, this idea's not possible without using ground wire, right?

Exactly - but there's no real difference between live (hot) and neutral (cold) anyway, it's just that the neutral is normally earthed at the sub-station - which is why you can get a shock from live (hot) to ground.

I also wouldn't be that trusting of RCBO's if you don't have an earth on your electrical system,

 

[ningole]

Exactly - but there's no real difference between live (hot) and neutral (cold) anyway, it's just that the neutral is normally earthed at the sub-station - which is why you can get a shock from live (hot) to ground.

I also wouldn't be that trusting of RCBO's if you don't have an earth on your electrical system,

Thank you for the additional information, it's really helpful !
After some research, I found another solution for this idea: use electromagnetic induction to detect the hot wire, it simply uses 3 transistors to amplify the signal from the antenna. I found this on YouTube:

Perhaps this is a good way to try.
Thanks again to rjenkinsgb & Nigel Goodwin for giving me clear instructions and explanations!
Have a good day!

 

[ZipZapOuch]

A $10 circuit tester will be safer, faster and cheaper than the OP's solution - the "trifecta" for an engineering solution.

There is a standard in the U.S. if the ground pin is mounted to the bottom, the HOT blade hole should be in the upper right. Neutral should be the taller blade hole.

Here is an Amazon link...

https://www.amazon.com/Gardner-Bender-GFI-3501-Receptacle-Extension/dp/B00170KUPC/ref=sr_1_1_sspa?dib=eyJ2IjoiMSJ9.svpbjDlqX4uo_ueqG5xxKVeBLNcfO2ihMdckqJ1yRWPPhu5T6W6VHcE3esLAzW8Pzykh9dXUsuZgUuGKJbv-ZRS5YXSJbzyqj092Luk35a0baD6JXvMgoG3fr35iHEijqG-om5-jo5fY0BjaQB3N7vUlI6481X0jQj3CjTqnE1yZu0bMcdDZL82rPBghseeKBxuwV7-9nhiZKqUFTjDf2CMnwn4n7OWe2H_LMDE4ZxxwnofslQjVhn-eyytHrlkosiBCfDRKbmaU2zHnRLNWkH8iCP-2cQ0QMGtbO9WUZKc.ycwo3ItRbfWNExVWuN0FhJw3Rw6L_Mmbszl_bEZAsg8&dib_tag=se&keywords=outlet+tester&qid=1711211309&sr=8-1-spons&sp_csd=d2lkZ2V0TmFtZT1zcF9hdGY&psc=1