I don't understand. Help me!

[Dat Tran]

I don't understand why the LED blink when i assemble circuit below:

https://youtu.be/KToYHIfOVcE

I use my body to conduct (any thing is conductive)
any idea help me
Thank in advance!

[8086]

Your image doesn't work.

[Dat Tran]

Yes. I fixed. Please explain me!

[continuo]

Was this video taken with your cellphone or do you happen to have any other wireless devices nearby? 

[homebrew]

Obviously the transistor starts to conduct. Hence there is some current flowing through your body.
The 2N222 has an hfe of around 50-100, thus the current through your body would only need to be around 0.1mA (or even less depending on the type of LED) to light up the LED.

Where does the circuit power come from?
Maybe an ungrounded SMPS? (Like a plugpack mobile charger?)

[Dat Tran]

I used a mobile charger 5V. it's nokia mobile charger

[retrolefty]

There is no resistor in series with the LED that would limit the led current to it's safe rated value. You are in danger of burning out either the transistor or the led if left on. Although I can't understand how the led could even light up with the base grounded. I suspect you have damaged parts or you didn't draw exactly what you built.

[Gixy]

You are 'earthed', not ´grounded'. Depending on your shoes, clothes, you potential is sufficient to polarize the transistor base. So it conducts but then, as retrolefty says, as there is no current limiting device, I suspect that your Nokia charger has too much current to source and maybe it's it which cuts power. And then the system recycles...

[kezat]

Could the power supply be going in to over current protection or if its a weak battery powered deal it could be osculating seeing no resistor is added.

[Dat Tran]

Hi,retrolefty. I don't understand why LED blink. But I draw exactly as I assemble. I sure

[Dat Tran]

Hey, Gixy. I don't wear shoes or any clothes on foot. My foot on floor without clothes. I don't sure about Nokia charger but it still work

[Psi]

Im going to go with the simple answer.

You used a 12V flashing LED, rather than a normal LED 

This explains why its flashing and why it didn't explode due to no current limit resistor.

Flashing LEDs have a resistor and flashing circuit built inside.

One way you might have come across a flashing LED is from an old car alarm.

You can normally see a black blob inside flashing leds if you look close enough.

[Dat Tran]

No, no, Psi. I used a normal LED. It has one anode and one cathode, not resistor.

[onlooker]

You should try a few things to get the mimimum setup for reproducing the flash and report back.

1. serial a  resistor to the led and power them with batteries. Do you still see flash?

2. Short  the emitter to GND and keep hands off (and using batteries). Do you still see flash? (You said any conductive?)

3. Use you finger touch only the emitter.

[AndyC_772]

I think the lack of an LED series resistor is the key. You've built an oscillator:

- current flows into transistor base
- transistor switches on
- LED lights
- power supply sees unexpected large current
- power supply protection circuit shuts off the supply
- LED goes out
- supply is restored
- goto 1

Try putting a 1K resistor in series with the LED and see what happens then.

[Gixy]

Hey Andy, that's what I suggested and the proposal of onlooker will allow to fix it.

[Dat Tran]

Hey, onlooker
1. I serial a resistor to led. When i touch the base-resistor, LED flashes once and then stabilize, not flashes again.
2. When i touch emitter, LED no flashes

Thank you so much

[Dat Tran]

Hey, AndyC_772

You are right. i learned about Nokia charger, it is true that it will shutdown when excessive current, after it auto restart.

[Dat Tran]

Thank all of you. i'm very happy because of explanation... One a gain, thank you so much