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Sequential start-up/shut-down circuits?

  1. Dec 30, 2007 #1
    Alright- to start with, I apologize if this is an easily remedied issue, or if I'm over-thinking it, but - here it goes.

    Using IC555's, I'd like to build a series of timer circuits that can power up a group of sound equipment with a specific timed procedure. As it is right now, myself and the other audio engineers at this location have to lap the building three times to get all five systems started, and to be frank, we're lazy, and would like to make the start-up process as "newbie-friendly" as possible.

    The systems have to start up with particular delays, as follows.
    1) Console
    7-second delay
    2) Monitor control system (Avioms)
    7-second delay
    3) Power rack
    15-second delay
    4) Main speakers
    2-second delay
    5) Monitor speakers

    Without the delays listed, it's possible to cause loud pops damaging to the human ears, or even severely damage some of the equipment in question. (Power-up pops can blow the main speakers pretty readily, and filtering them out is VERY costly. We simply cannot afford the price of the filters.) Also - they have to power down in exactly the opposite order they were powered up, with the same time delays going in the other direction.

    Now, here goes my thoughts/designs/possibly idiotic musings.

    What I originally wanted to do was build a timer circuit for each system such that a momentary contact pushbutton powers on the console, then starts a 7-second timer, which then, at the end of 7 seconds, trips the second relay, and starts another 7-second timer, which, at the end of 7 seconds, trips the third relay, and starts a 15 second timer...etc.etc.etc. to basically go through a fully automated power-up sequence. Then for the power-down sequence, have a series of timers going the opposite direction which, at the end of their times, they send a pulse to the first set of timers to stop outputting voltage to the relays to power them off.

    Here's the problem.

    An IC555 monostable timer only goes high for the number of seconds decided by using the resistors and capacitors, then drops low again. What this will do is trip the relay, leave it on for x number of seconds, and drop low. This is a problem.

    Example: Timer 3 is using a 1M resistor and a 10µF capacitor. So - it's low, gets triggered, goes high for 15 seconds, then goes low again. So - the main speakers would turn on for 15 seconds at the beginning of the cycle, and turn off again.

    How I decided to try to fix the problem.

    Get the inverse of the output of a 555 monostable timer, and use that to pulse to a 555 bistable latched switch. Problem. The 555 bistable goes high the instant the trigger pulse drops low. Not at the end of the pulse. So - there's no delay. But the bistable latched circuit does what I need it to do. Output high on pulse, and stay high until a pulse comes into the reset pin (4) to power it off. But - the timer still doesn't do what I need it to do (wait 'til x number of seconds passes, then go high.).

    Now here's my question.

    Am I over-complicating things horrendously again? Is there a timer circuit I can build that outputs low, takes an input pulse, stays low for X number of seconds, then goes high and stays high until the reset pin is pulsed? In any case, is what I'm trying to do here remotely realistic? Or am I just having illusions of grandeur?
  2. jcsd
  3. Dec 31, 2007 #2


    User Avatar

    Staff: Mentor

    Can you run wires to the stations, and control the power switches from one location? Alternately, you could use powerline communication to turn on the remote power switches from a central computer location. You wouldn't want to use X-10 for the powerline control, since it isn't reliable enough to ensure that the messages got through. But there are alternate powerline comm technologies that are very reliable, and not all that expensive. My company offers good powerline comm technology, but I probably shouldn't link to that here (advertising -- the other Mentors would have a field day with me). Here's another company with similar powerline capability:

  4. Dec 31, 2007 #3
    if you had any kind of FPGA or CPLD dev kit you could program those delays and get the signals out in about 20-30 minutes of design. Would be a lot more simple than using 555 timers. you can get a spartan3 kit for around $100
  5. Jan 5, 2008 #4
    you just need a latch behind each timer....
    http://en.wikipedia.org/wiki/Latch_(electronics [Broken])
    Last edited by a moderator: May 3, 2017
  6. Jan 5, 2008 #5
    We've decided to use a programmable logic controller at the heart of the system, instead of timing circuits. Reverted to my software roots instead of the hardware design out of lack of time. But - there's a couple problems with using latches behind each timer circuit.

    1) A timer will stay low until it gets input, goes high until the capacitor discharges, at which point it goes low again.
    2) The latch will go high and stay high at the beginning of the timer's pulse, not the end of it.
    3) Even if I used an inverter on the timer's output to keep it high, drop low for x amount of time, then pull high again, and used a bistable 555 latching circuit as a "relay controller", the problem still remains about the timing pulse. The latch goes high at the beginning of the pulse, not the end, eliminating the timer's effectiveness.

    Instead, what we've done, is get a PLC with 16 inputs or outputs available, wired a momentary contact pushbutton as the only input, and had a few outputs as well. All of the timing is being controlled by the PLC. The PLC's outputs are wired to an inverter (to get an always-high, with low pulse output) to allow the 555 bistable latches to operate properly, which control the individual relays.

    Momentary contact drops voltage into the PLC. If the voltage drop lasts longer than 500 milliseconds (0.5 seconds), and the system is in standby, the standby red LED turns off, and a yellow LED is illuminated, and the startup process begins. The PLC acts like a series of cascading timers, triggering each output pulse to the inverters when they're supposed to be triggered, tripping the 555 latch, causing the devices to power on. When the startup process is complete, the yellow LED turns off, and a green LED is illuminated. To power off the system, the same momentary contact pushbutton needs to be held for 1500 milliseconds (1.5 seconds), then the shut-down procedure begins (green LED off, yellow on.). Timers run internally, and a whole new set of outputs operate. The outputs are wired to similar inverter circuits, but instead of being wired to the trigger pins of the bistable 555's, they're wired to the reset pin (4) which pulses to deactivate each circuit, powering off the relays, and thus the devices one by one at their proper times. When the shut down process is complete, the yellow LED turns off, and the red one turns on. Lastly, we've created a feedback loop from the yellow LED output to create a second "input" for the PLC to avoid taking up extra program space with if/then statements. What this feedback loop does is, while the yellow LED is lit, the momentary contact pushbutton is disabled. This makes it so you cannot initiate a startup or shut-down procedure while the device is already going through its processes, otherwise, you end up creating a dangerous infinite loop that could potentially damage expensive audio equipment.

    I do appreciate the help, everyone, and I will be using this as not only a controller for the auditorium, but for massive extra credit where needed. :) Thanks again!
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