Help with sequential LED delay - 555 Timer

Discussion in 'Digital Circuit Design' started by preetham29, Jun 25, 2018.

  1. preetham29

    Thread Starter New Member

    Jun 21, 2018
    2
    0
    I need help with the series of monostable configuration of 555 Timers. The idea is to light up the different LEDs with different timings triggered by the falling edge of the previous timer, with the initial monostable setup being triggered by the switch. The first LEd lights up for 3 mins , then the next for 1 sec and the next for 1 min and so on for six LEDs.
    However when i'm running the simulation in multisim , all the LEDs are already initially lit up except the first one. Can you please tell me what i'm doing wrong?
    Any other ideas to light up LEDs one after another with their individual timings? i'm attaching the image below ( Ignore the resistor values , they're approximate , my issue is the LEDs lighting up without the previous 555's trigger as soon as i run the program )
    mono_trigger.PNG
     
  2. bertus

    Administrator

    Apr 5, 2008
    18,365
    3,518
    Hello,

    Perhaps you will need a power on reset.
    Also the leds do not have any current limiting resistors.

    Also the triggeling should be different.
    Have a look at the schematic from the TI datasheet:

    NE555_sequential timer.png

    Bertus
     
  3. preetham29

    Thread Starter New Member

    Jun 21, 2018
    2
    0
    Thank you so much ! I'll read and try it out.
     
  4. danadak

    Well-Known Member

    Mar 10, 2018
    1,460
    300
  5. crutschow

    Expert

    Mar 14, 2008
    19,545
    5,447
    How is that possible for 6 LEDs? :confused:
     
  6. crutschow

    Expert

    Mar 14, 2008
    19,545
    5,447
    The 555 Trigger input is a level detect, not edge detect, and at power-up all the 555 inputs are low so they all trigger on.
    Thus the trigger inputs need to be AC coupled so they respond to the negative signal edge, as shown in bertus's post.
     
  7. danadak

    Well-Known Member

    Mar 10, 2018
    1,460
    300
    His timing diagram shows one led on at a time, so two leds/pin,
    one source drive, one sink drive, tristate both off. 3 pins. 1 pin
    for switch.

    Or one led / pin, switch turns on power to ATTINY to initiate sequence.
     
  8. crutschow

    Expert

    Mar 14, 2008
    19,545
    5,447
    So you have one ATTINY per LED?
     
  9. danadak

    Well-Known Member

    Mar 10, 2018
    1,460
    300
    1 ATTINY, 6 LEDs, 6 LED Rilims, 6 GPIO pins,
    a switch as power switch for ATTINY to turn it
    on and issue the sequence.

    OR

    1 ATTINY, 6 LEDs, 3 LED Rilims, 3 GPIO pins (2 LEDs/pin),
    a switch as input to a pin to trigger the sequence.

    for both a power source, and a bypass cap.

    On power up GPIO pins in HiZ.

    Total timing accuracy +/- 1% with user cal at test, or +/- 10% without.
     
    Last edited: Jun 25, 2018
  10. ElectricSpidey

    Member

    Dec 2, 2017
    443
    95
    The circuit posted by Bertus is ok, but with the outputs connected to ground via a LED and resistor I would worry about how the circuit will behave from startup, and probably drop in a RC net at each reset to insure they all start low.

    The first one also needs a pullup resistor at the trigger, to avoid spurious starts. (not to mention the problems concerned by that switch also missing an AC input if the first timing cycle has to be shorter than the button push)
     
    Last edited: Jun 25, 2018
  11. eetech00

    Senior Member

    Jun 8, 2013
    1,123
    227
    HI

    Here's an option using CD14538B's.
    I didn't draw the all six timers but three more could easily be added.
    Each timer triggers on the falling edge of the previous timer

    eT

    SequencialTimer.png
     
  12. danadak

    Well-Known Member

    Mar 10, 2018
    1,460
    300
    Last edited: Jun 26, 2018
  13. crutschow

    Expert

    Mar 14, 2008
    19,545
    5,447
    There is no current limiting for the two LEDs in series to the supply.
    And how can you turn off all the LEDs with that circuit?
     
    bertus likes this.
  14. danadak

    Well-Known Member

    Mar 10, 2018
    1,460
    300
  15. danadak

    Well-Known Member

    Mar 10, 2018
    1,460
    300
    Last edited: Jun 26, 2018
  16. AnalogKid

    AAC Fanatic!

    Aug 1, 2013
    7,010
    1,986
    Since none of the resets are used to control any outputs, one R-C network can drive all reset pins.

    ak
     
Loading...