Two simple 555 circuits that don't combine

Discussion in 'The Projects Forum' started by lost_bro, Feb 28, 2011.

  1. lost_bro

    Thread Starter New Member

    Mar 17, 2009
    9
    2
    Good Day All

    To make this brief as possible so as not to take up to much of anyone's time:

    I have two 555 timer type circuits that I want to combine to form one new circuit.

    I have included both circuits in PDF and LTspice files in the Zip file attached.

    I have spent many hours trying to find my mistake with these two circuits.
    I know both circuits work. As they simulate when separate just fine.

    The problem is when I try to make both circuits run off of the same power source in LTspice.
    The circuits do not give the required output. In other words when combined they no longer function as when running separate.

    I have included also my best attempt at combining the two circuits. It doesn't simulate correctly either.

    The first circuit (left side) on the sheet is just a hi-low voltage disconnect which activates a simple relay to run the load.

    The second circuit (right side) is a time delay and LED flasher to show the status of the relay.

    The first circuit can have it's relay and supporting transistor removed and the output from second 555 going directly to activate the second delay/flasher circuit. This is what I attempted to do in the second file/PDF where both circuits are seeming united.

    I would appreciate any thoughts or insights on this.
    I am surely overlooking a very simple solution, although I have spent almost two days on this now.

    Thanks in advance.
    Lost_br0
     
  2. nb99

    New Member

    Feb 28, 2011
    4
    2
    In the 3rd 555 ( U8), DIScharge tied to Vcc doesn't look right.
    And unless you have some reason to switch the ground to U7 and U8, why not use the O/P directly from U2 to control the RST on U8?

    nb
     
  3. lost_bro

    Thread Starter New Member

    Mar 17, 2009
    9
    2
    Good evening nb99
    Thanks for the reply:
    Well I have tried the reset, connecting the OUT of U2 to Rst U8.

    Basically what I want to do is combine the two circuits so when the OUT of U2 is Hi, the 555 U8 will power-on and begin its timingDelay/flashing routine, which eventually powers up the load/relay on U8's OUT.

    Once I combine the two circuits the load/relay and controlling trans. on the OUT of U2 will be eliminated , leaving just the load on the OUT of U8 operational.

    The problem is that when ever U8 powers up, it automatically begins to time it's delay and flash the LED.
    The reset does not stop the power up routine.
    This is why I was trying to switch the grounds on U8 and U7.

    I know I am missing some fundamental process here, that would allow the connection between the two circuits.

    I would greatly appreciate any more pointers.
    Thanks
    Lost_brO
     
  4. nb99

    New Member

    Feb 28, 2011
    4
    2
    I think you need to lay out exactly what the sequence is supposed to be.

    Is the main load supposed to be on Q3 or Q2 when you combine the circuits
    Because it appears that on power up you have the delay on U8 holding Q3 off (and U7/D13 flashing).
    At the end of the delay U8 goes low and turns Q3 on. (and stops U7/D13 flashing).

    So U8 will always go through that sequence when powered up.

    Then you have what looks like a low voltage detect with U1 - but what is U2 supposed to detect. It only has TRIG sensing the voltage source, but that is also a low voltage trigger? Should the pot on U2 be going into Thrsh to detect high voltage?

    Removing Q2 and associated Rs, you should then be able to use the o/p of U2 going low on over/under voltage to set U8 hi (and turn off Q3) with the following

    U8 trig U8 thr
    U2 o/p o--|<----o----WWW----o------ existing circuit
    diode 100k
     
  5. lost_bro

    Thread Starter New Member

    Mar 17, 2009
    9
    2
    Good morning nb99

    Hey, thanks alot for the time. I appreciate it!

    OK,
    **Is the main load supposed to be on Q3 or Q2 when you combine the circuits
    Because it appears that on power up you have the delay on U8 holding Q3 off (and U7/D13 flashing).
    At the end of the delay U8 goes low and turns Q3 on. (and stops U7/D13 flashing).

    ^Exactly correct, upon power up everytime U8 will delay (U8 OUT high) and Q3 will flash until the delay ends (U8, OUT goes low) and Q3 will light up constantly. Also simultaneously the load 12 (relay) will energize.

    **So U8 will always go through that sequence when powered up.
    ^Yes, by design it does this.

    **Then you have what looks like a low voltage detect with U1 - but what is U2 supposed to detect.

    ^U2 is the High voltage detect.

    ** It only has TRIG sensing the voltage source, but that is also a low voltage trigger? Should the pot on U2 be going into Thrsh to detect high voltage?

    ^Both halves of the circuit function perfectly independantly of each other.
    I tried to connect pot to Thrsh, but does not signal correctly.
    It does simulate perfectly as wired. For example with the voltage source set at 13.22 voltsv(out of voltage range), U2 OUT goes Low and the relay would disconnect. At 13.21 volts (inside voltage range) U2 OUT is High and the relay continues to be energized, according to design.

    **Removing Q2 and associated Rs, you should then be able to use the o/p of U2 going low on over/under voltage to set U8 hi (and turn off Q3) with the following

    ^Yes, this is what I want to do.

    **Removing Q2 and associated Rs, you should then be able to use the o/p of U2 going low on over/under voltage to set U8 hi (and turn off Q3) with the following

    I have included some new pic.s from LTspice.
    As connected in the diagram included:
    -When outside of Voltage range, U8 OUT always high and LED flashes forever and Relay never energizes. This is correct as outside of range It should not energize but likewise D13 should not either, and it does (flashes).
    -When inside voltage range, The cycle starts normally, U8 OUT high, and then timer expires and U8 OUT should go LOW, but it begins to oscillate like a PWM gone mad. See attachment. This make Load 13 (Relay) oscillate also. Not good!
    -With the U8 Thrs disconnected, It flashes D13 forever and U8 OUT is always High.
    -With U8 Thrs & Trig connected to U2 OUT, in voltage range U8 OUT Oscillates from the get go. NO delay, total malfunction. See attachments.

    I'm kind of confused at this point. I don't want to give up on this just because I'd rather spend the time to and learn what I've done wrong here.

    Thanks for the patience with my questions.

    Take care
    Lost_br0
     
  6. nb99

    New Member

    Feb 28, 2011
    4
    2
    U8 will probably be oscillating because of having Discharge connected - as I earlier mentioned .

    Try the attached circuit arrangement round U8.

    nb
     
    lost_bro likes this.
  7. lost_bro

    Thread Starter New Member

    Mar 17, 2009
    9
    2
    Good evening nb99

    Thanks for the helpful info.
    Please check attachment.
    It is wired as you suggested, and Yes the 3rd 555 (U8) is now functional!:D
    Thanks...

    U7, still I must figure out how to connect it correctly.
    The circuit as posted runs the hi-low disconnect correctly, activating U8 as desired.
    On Over or Under voltage conditions, U7 just blinks its LED D13 infinitely.
    Of course when the voltage is within range, D13 blinks as supposed to and after time-out, lights up solid, just as it should.
    I would like to find a way so it is off, not blinking, in the over/under voltage conditions.
    I have tried various connections to the trig/thrs.
    Also I tried to switch the ground and Vcc again to control when it energizes.

    By design,, whenever it powers up (U7), it will start blinking D13 until reset.

    I will have to think about this some more.
    Any suggestion would be helpful.
    Thanks nb99

    Take care
    Lost_br0
     
  8. nb99

    New Member

    Feb 28, 2011
    4
    2
    You have specified 3 states for U7 - so you need an extra control input to set the o/p hi and the LED off on over/under voltage.
    See attached U7 circuit.

    nb
     
    lost_bro likes this.
  9. lost_bro

    Thread Starter New Member

    Mar 17, 2009
    9
    2
    Good evening nb99

    Thanks for the pointers!
    After rearranging U7 as recommended the entire circuit is working as planned. :D:D:D
    I appreciate all the help, Thanks...

    Take care
    Lost_br0
     
  10. BEBEH

    New Member

    Jul 24, 2011
    1
    0
    can i know the function that circuit you combine?? and how it's work..

    sorry my English not good :)
     
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