×
INTELLIGENT WORK FORUMS
FOR ENGINEERING PROFESSIONALS

Log In

Come Join Us!

Are you an
Engineering professional?
Join Eng-Tips Forums!
  • Talk With Other Members
  • Be Notified Of Responses
    To Your Posts
  • Keyword Search
  • One-Click Access To Your
    Favorite Forums
  • Automated Signatures
    On Your Posts
  • Best Of All, It's Free!
  • Students Click Here

*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail.

Posting Guidelines

Promoting, selling, recruiting, coursework and thesis posting is forbidden.

Students Click Here

Jobs

astable ajustable timer to pulse 30 secs to 5 mins question

astable ajustable timer to pulse 30 secs to 5 mins question

astable ajustable timer to pulse 30 secs to 5 mins question

(OP)
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

RE: astable ajustable timer to pulse 30 secs to 5 mins question

James,

Did you have a chance to take a look at a 555 timer application data sheet?  Try looking at www.national.com and look up the LM555 timer.  Perhaps something there might give you some ideas.

Keep us posted!

RE: astable ajustable timer to pulse 30 secs to 5 mins question

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>

RE: astable ajustable timer to pulse 30 secs to 5 mins question

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.

Red Flag This Post

Please let us know here why this post is inappropriate. Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework.

Red Flag Submitted

Thank you for helping keep Eng-Tips Forums free from inappropriate posts.
The Eng-Tips staff will check this out and take appropriate action.

Reply To This Thread

Posting in the Eng-Tips forums is a member-only feature.

Click Here to join Eng-Tips and talk with other members!


Resources