Hi, all!
LM555 timer is an integrated circuit chip, often[used in timers, pulse generators and oscillator circuits. LM555 can be used as a delay device, trigger or start-up element in the circuit. but how to trigger phase control with an LM555 timer? The waveform of the upper end of the 12V voltage is given below
Could anyone give some suggestions? Thanks, advanced!
With some research, pin 7 can be used to change the firing angle of the 555 timer.
That circuit is a bit lethal as it is directly connected to the mains and that ground connection is at live potential every half mains cycle.
Any measurement with an oscilloscope is likely to result in a big bang unless you have an isolated probe, which will probably cost you more then the scope itself.
The NE555 should be used as a monostable to get the firing angle to change and your circuit should be isolated with an opto isolator on the trigger input and an other on the gate of the SCR.
That LM555 thing looks way useful!
a7
Well, you now have some suggestions, mainly, don't try to use that circuit. 
What do you actually want to know - or do? 
Don't try to use that circuit？ what is it mean? I do not understand completely.
If you don't know what you are doing you can easily kill somebody. A lot of dangerous features in the circuit.
So reply #3 went right over your head?
If so why did you not say?
I am trying to save your life here, Google “Darwin Awards”
Yep!
Thanks for ur suggestion. I think I got it!