astable ajustable timer to pulse 30 secs to 5 mins question

I am looking for a schematic thats simple using a pot to adjust my timing.. final output would look like this

______|______|_______
30secs 30secs 30secs

ajustable to
_______________|_________________|_________________
3mins 3mins 3mins

the pulse can vary but has to be relatively short, .5 secs is ok. i have 5 volts dc as power supply and think a 555 will work but I dont know the best way to do it..

can anyone help me? many thanks in advance if you can..

james

 

[melone]

James,

Did you have a chance to take a look at a 555 timer application data sheet? Try looking at

http://www.national.com

and look up the LM555 timer. Perhaps something there might give you some ideas.

Keep us posted!

 

[nbucska]

If the time set must be stable, you may consider running it at higher FR. and dividing down

Better accuracy requires crystal clock -- divider.

<nbucska@pcperipherals.com>

 

[biomedicalEng]

555 can handle your purpose.
in astable configuration the pulse period is equal to
T=.693*C*(2Ra+Rb)
where Ra is resistor between pin number 6 and 7
and Rb is resistor between pin number 7 and 8 or Vcc (+5)

high time=.693*C*(Ra+Rb)
low time =.693*C*Ra
you can make very large duty cycle with choosing Ra a very low value and Rb many times greater than Ra
then you can invert the signal with a simple not gate
(74LS04).
if you still don't understand how circuit works let me know.