# how to control phase pluse wave (555timer)

Discussion in 'General Electronics Chat' started by metalucard, Mar 22, 2006.

1. ### metalucard Thread Starter New Member

Mar 22, 2006
3
0
hi,
I am currently working on a challenging project, I have to to make 4 mechanisms launch balls, so I thought I could use the 555 timers to control the timing of the mechanisms, now the only problem is that the 555timer typical ouputs low for a certain period of time at the beginning, but I need to control the phase of the 555timer pulse wave, so, for instance the first 555timer has to go high right from the beginning, and then oscillate between t1 and t2 in astable mode, the second 555timer has to go low for some time ts and then oscillate between t1 and t2, well you get the idea, I though i could do something with the initial charge of the capacitor at but I don't really have any clue. please I need some advice

2. ### pebe AAC Fanatic!

Oct 11, 2004
628
3
Your query is a bit vague. Can you put times to the sequence of events?

3. ### metalucard Thread Starter New Member

Mar 22, 2006
3
0
sorry, I will try to make my post clear.
so my objective is to produce through some kind of timing circuit, a pulse wave that goes low for a time we call t1, and goes high for a time we call t2. the pulse wave will oscillate between low and high at their respective times. untill now, it seems that a simple 555timer in astable mode can do the job easily. now here is where I am stuck: when using the 555timer in astable mode, the pulse wave (output of the 555timer) starts by going LOW for a specefic period of time, (the time for the capacitor to charge and drop the voltage at the trigger to below 1/3 Vcc).
Now I want to do, is to be able to control the phase of the pulse wave (just like we can set the phase of a sine wave). so for instance, my pulse wave (the output of my timing circuit will go high right a way when I close the switch.
this is a sample of a regular 555timer pulse wave (astable mode):

t=0: __________|'''''''''''''|__________|'''''''''''''|__________|'''''''''''''|

here are 2 examples of what I want the timing circuit to produce:

t=0:____|'''''''''''''|__________|'''''''''''''|__________|'''''''''''''|

t=0:_|'''''''''''''|__________|'''''''''''''|__________|'''''''''''''|

notice that in both examples, it is the same typical 555timer wave, but the phase is different.
and just in case, this is the website I got my information from about making a regular 555timer circuit in astable mode:

4. ### metalucard Thread Starter New Member

Mar 22, 2006
3
0
can any one give me any idea or help. I don't mind looking stuff on my own, but this time I am really stuck, I don't know where to look, so please help me.

5. ### thingmaker3 Retired Moderator

May 16, 2005
5,072
6
Looks like there are a couple options...

One - You could try to synchronise four astables, simultaneously control their PWs, and attempt to introduce uniform phase shifts between them. Option one is not something I would attempt. (I'm not saying its bad, just that I would personally not like it. Too much fuss.)

Two - You could use a single astable and some logic to trigger four monostables in sequence. Adjusting the frequency of the astable would control the phase delay between the monostables. Using a counter and gates could control period between monostable triggering. A second astable driving the counter might allow more flexibility.

6. ### thingmaker3 Retired Moderator

May 16, 2005
5,072
6
Something like this:

[attachmentid=1314]

Astable One would run at a bare miniumum of 4x Astable Two. #One controls phase shift and #two controls frequency.

Of course, this won't work if phase shift exceeds period.