• State Resolved
  • Locked Locked
  • Replies 3 replies
  • Subscribers 22 subscribers
  • Views 1344 views
  • Users 0 members are here
Support feedback
Options
Options
Related

This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

555 timer stability

Andrew Humber
Prodigy 10 points

My 555 timer isn't doing what it should do, or maybe it's just me?

I have a 555 timer circuit operating as an extended duty cycle astable timer.  The frequency generated is used to switch high power LED's which 'strobe' to freeze the motion of a spinning sculpture.  Basically a stroboscope.  This is all good, I have tantalum type capacitors, metal foil type resistors and they all give a good clear signal.  The only problem is that over time (90 sec) the frequency of the flashing LEDs increase so the spinning wheel is not frozen, but scrolling the other direction.  The same thing happens time and time again.

What's going wrong?  I have 5, 47uF capacitors in series could this cause some kind of build up over time?  Is it the type or quality of the 555 timer?  The 555 operates a mosfet which switches the high power LEDs, could there be something there?  The wheel is spun by an invertor driven three phase motor.

Please help.  I feel like I'm going round in circles, that's the problem.

  • 0
    TI__Guru**** 164486 points

    I have a 555 timer circuit operating as an extended duty cycle astable timer. 

    Extended duty? I’m not familiar with that term.

    The only problem is that over time (90 sec) the frequency of the flashing LEDs increase so the spinning wheel is not frozen, but scrolling the other direction.

    May I assume that you set the frequency manually to match the spin rate? This is not reliable as the object spin rate or 555 frequency can vary slightly over time, temperature, wind, and many other factors.

    You need to get a signal that is synchronized with the spin rate. This will ensure a matching spin and flash rates.

    I have 5, 47uF capacitors in series could this cause some kind of build up over time?

    Series capacitors do not always share the voltage equally. Is this part of the timing circuit? Why are they in series?

    Is it the type or quality of the 555 timer?  The 555 operates a mosfet which switches the high power LEDs, could there be something there?  The wheel is spun by an invertor driven three phase motor.

    I do not see a problem with this.

  • 0
    Prodigy 160 points

    Print out the datasheet for the 555 timer and look at the equations, if your resistors and capacitors aren't calculated correctly, you may have small buildup in the capacitors over time.

  • 0 in reply to Joshua Zenn
    Prodigy 160 points

    Sorry, i meant to say if your capcitor and resistor VALUES weren't calculated correctly, you can have small voltage buildup that can be released off pattern and confuse the 555 timer.