Help regarding 555 timers and 4017 counter

Discussion in 'The Projects Forum' started by JingleJoe, Jul 23, 2011.

  1. JingleJoe

    Thread Starter Member

    Jul 23, 2011
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    I'm working on a 4017 based counter circuit, I have the counter part working fine with transistorized outputs going to LEDS, however I want to use this circuit to activate 555 timer astable circuits for different lengths of time. I have come up with two variations utilizing 555 timer monostable circuits to activate the astable circuits, (see attached files for block diagrams) I know there's some resistors missing, like the pull down resistor on the astable reset and a base resistor on the transistors, but you can get the idea.
    I have some questions regarding the points where chip pins are going to the same connections.

    Some further explanation of the operation of both circuits may be in order first;
    Circuit 1 can activate the monostable for periods shorter than the counter output pulse, as it resets the monostable on the next count. However I don't know if diodes would be required at certain points to separate the chips where they connect to the transistor?
    Circuit 2 stops the counter chip when the monostable circuit is activated, thus allowing longer counts than the clock speed going to the 4017. But could more diodes be required here? between the monostable outputs and the 4017? between the astable and monostable too?

    Lastly I would like to know if you think the transistor stages would function correctly? They are just acting as switches, which are normally high and go low when activated.


    Please ask for clarification if I have missed anything, I think it's all there.

    One last note about the diagrams, the circle at the top of the transistor stage would be connected to +V or Vs or whatever you want to call it :p
     
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  2. praondevou

    AAC Fanatic!

    Jul 9, 2011
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    1. yes the diodes are necessary, one from each monostable output to the clock enable input (cathode joined). You also should put a pull-down resistor from the clock enable to GND then.
    (You are aware that you stop the counting process completely, thus all Q's from your counter remain steady for the time the monostable output remains HIGH)

    2. The transistor stages should work. (as you said, base resistor missing :))

    in this circuit, Q1 sets the 1. monostable, then it is being reset by Q2, right. But then the output pulse of this monostable can NOT be shorter than the counter output pulse (Q1), because if I look at the timing diagram, there is never more than one output active.
     
  3. JingleJoe

    Thread Starter Member

    Jul 23, 2011
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    yes exactly as I was planning :) Thankyou very much for clarification of my diode related suspicions.
    EDIT: Just to clarify one more thing, what do you mean by cathode joined? My initial thoughts were the anode towards the 4017 and cathode towards the 555 output?

    It's correct that there is never more than one output active however I think I did not explain clearly enough, rather the monostable can be set for a time period no longer than the chip output is high, but instead for a shorter ...
    oh wait, if the trigger remains activated then will the 555 output still be high even beyond the time set by the monostable circuit? I thought I could stick a capacitor in there somehow to remedy this and make it edge triggered?

    Thanks again for the previous information, greatly helpful :D
     
    Last edited: Jul 23, 2011
  4. praondevou

    AAC Fanatic!

    Jul 9, 2011
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    yes, you can do this. put a cap in series to the trigger input and a pullup resistor on the trigger input. I'd also put a fast diode (e.g.1N4148) from trigger to +, I'm not quite sure anymore, but I believe to remember that I killed several 555 because the trigger input exceeded the Vcc.
     
  5. JingleJoe

    Thread Starter Member

    Jul 23, 2011
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    Spiffing, thankyou :D

    Would you be so kind as to clarify the direction of the diode you mentioned by cathode joined?
     
  6. praondevou

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    Jul 9, 2011
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    connect one diode at each monostable output (anode at monostable), put the cathodes together and connect them to the clock enable of your counter.

    when the monostable gives a positive pulse you won't short it with the other monostable in case the other one is LOW.
    don't forget the pulldown to bring the clock enable into a definite state in case both monostables are off.

    (I hate when they label something "enable" and then it's disabled when on HIGH:D)
     
  7. JingleJoe

    Thread Starter Member

    Jul 23, 2011
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    Thankyou again for the very clear explanation, I'm not new to this but diodes and anodes and cathodes allways confuse me a bit, I'm starting to get my head around it more now though.

    YES! That is precisely the kind of thing that confuses me!
     
  8. KJ6EAD

    Senior Member

    Apr 30, 2011
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    You didn't say what this was all for but I suspect the creation of some infernal steampunk contraption using a 4017 as an effects sequencer.
     
  9. JingleJoe

    Thread Starter Member

    Jul 23, 2011
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    Almost, you will have to wait and see ;)

    I have some more simple questions regarding connecting things together, to answer before I can complete things though.
    Attached is a more complete block diagram/connection diagram (there are enough components in it that it doesn't really feel like a block diagram but it's not quite a circuit digram ... blorcit diagram? Anyways ...)
    Firstly I'm wondering about the pull-down resistor required on the 4017 enable and astable reset, seeing as they are both connected via the diode, will the pull down resistor on the 555 astable reset also "pull down" the 4017 enable? or does it require it's own separate resistor?

    I am also wondering how to couple together the outputs, I plan to put them all through a voltage divider (hopefully just one so I don't need 20 :( more resistors!) however, do they require diodes between them so that the deactivated chips do not sink power from the output of the one oscillating chip?
    Thinking about it a bit more, this would of course depend on whether the chip's output was high or low when deactivated, if high, then I think a cap would suffice, however if low, I suspect it'll be "sinking" current and require a diode as in the diagram, am I right?
     
  10. praondevou

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    Jul 9, 2011
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    Put only ONE pull down resistor directly at the 4017 input (cathode of diodes). remove the resistors on the resets of the astable 555s.

    The left side of the caps in series with the diode will eventually charge to +Vcc and remain charged, this is not going to work.

    I guess I didn't understand what's this circuit for, wasn't it to drive one LED with each astable?
    Anyways, if you want to join the signals in an OR function you can do it the same way: diodes at the output of each astable with ONE pulldown resistor at the cathodes. you can also use a logic gate like the 4072, a 4-input OR gate.
     
  11. JingleJoe

    Thread Starter Member

    Jul 23, 2011
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    Sorry, I should have been clearer. Thats what I got my counter doing already; Lighting LEDs in sequence, just to test if it works. Now it's time for some more interesting things.
    You have been my saviour on this project, thankyou! :D
     
  12. JingleJoe

    Thread Starter Member

    Jul 23, 2011
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    just posting a revised version of my schematic
     
  13. praondevou

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    Jul 9, 2011
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    Looks good.

    As already mentioned, if you want to triger the monostable with just a short pulse, put a small (max 1n) capacitor in series and a pullup resistor and a towards + pointing signal/schottky diode at the trigger input.

    If you want to drive LEDs directly from your OR'ED output AND you want to derive the signal for something else (for some other digital circuitry etc) you'd have to put only one low-resistance series resistor for each LED and the voltage divider in your circuit could have higher resistance.
     
    Last edited: Jul 26, 2011
  14. KJ6EAD

    Senior Member

    Apr 30, 2011
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    For each of the monostable/astable blocks you can use a 556 dual timer. I don't think you need the trigger transistors. You should be able to use a pulse forming capacitor and pull up resistor as in this partial simulation.

    http://www.falstad.com/circuit/#%24+3+0.0020+1.9265835257097934+51+5.0+50%0A163+232+328+256+328+1+10+0.0+5.0+0.0+0.0+0.0+0.0+0.0+0.0+0.0+0.0%0A165+136+312+168+312+3+5.0%0AR+168+296+168+264+0+0+40.0+5.0+0.0+0.0+0.5%0Ac+168+392+168+424+0+1.0E-8+3.333333333333333%0Ag+168+424+168+440+0%0Ar+136+328+80+328+0+10000.0%0Ar+136+360+80+360+0+47000.0%0Aw+136+376+80+376+0%0Aw+136+376+136+360+0%0Aw+136+328+136+344+0%0Aw+136+344+80+344+0%0Aw+80+344+80+360+0%0Aw+80+328+80+296+0%0Aw+80+296+168+296+0%0Ac+80+376+80+424+0+1.0E-5+2.6906802531305%0Aw+80+424+168+424+0%0Aw+168+296+200+296+0%0Aw+200+296+200+328+0%0A165+248+64+264+64+3+5.0%0Ag+280+176+280+192+0%0Ac+280+144+280+176+0+1.0E-8+3.333333333333333%0Aw+192+176+280+176+0%0Ac+192+128+192+176+0+1.0E-5+0.9353064673568369%0Aw+248+128+192+128+0%0AR+280+48+280+16+0+0+40.0+5.0+0.0+0.0+0.5%0Aw+248+80+248+96+0%0Aw+248+96+192+96+0%0Aw+192+96+192+128+0%0Aw+312+80+312+48+0%0Aw+312+48+280+48+0%0Ar+248+112+184+112+0+10000.0%0Aw+184+112+184+80+0%0Ar+248+80+184+80+0+100000.0%0Aw+280+48+184+48+0%0Aw+184+48+184+80+0%0Aw+200+344+232+344+0%0Aw+392+272+480+272+0%0Ac+392+224+392+272+0+1.0E-6+3.298313361794461%0Aw+392+144+480+144+0%0Aw+392+176+392+144+0%0Aw+392+192+392+208+0%0Aw+448+192+392+192+0%0Aw+448+176+448+192+0%0Aw+448+224+448+208+0%0Aw+448+224+392+224+0%0Ar+448+208+392+208+0+47000.0%0Ar+448+176+392+176+0+10000.0%0Ag+480+272+480+288+0%0Ac+480+240+480+272+0+1.0E-8+3.3333333333333335%0AR+480+144+480+112+0+0+40.0+5.0+0.0+0.0+0.5%0A165+448+160+480+160+3+0.0%0Ar+512+192+568+192+0+220.0%0A162+568+192+568+240+1+2.1024259+1.0+0.0+0.0%0Ag+568+240+568+256+0%0Ar+512+176+568+176+0+10000.0%0Aw+568+176+592+176+0%0Aw+592+176+592+240+0%0Aw+592+240+568+240+0%0Aw+512+96+512+176+0%0Ac+248+112+248+312+0+1.0E-6+4.999999996073919%0Aw+312+96+352+96+0%0Aw+352+96+512+96+0%0Ad+352+96+352+136+1+0.805904783%0AR+392+360+392+392+0+0+40.0+5.0+0.0+0.0+0.5%0A
     
    Last edited: Jul 26, 2011
  15. praondevou

    AAC Fanatic!

    Jul 9, 2011
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    You're right about the 556, the only difference will be without trigger transistor the monostable will trigger on the falling edge of the counter output pulse. I think the OP wants it to trigger on the rising edge.
     
  16. JingleJoe

    Thread Starter Member

    Jul 23, 2011
    185
    10
    Yes I do :)

    I am using 556 chips but didn't think to make the monostable and associated astable on the same chip untill after I'd finished both rows of astable circuits and monostable circuits. Anyways, this will work, just needs more wire, which I have tons of (I once raided a skip outside a closing down computer shop, only wish I'd gotten more, the stuff I did get is a bit crap but fine for circuits like this)

    Wondeful simulation too thankyou, I think you are right, I could do without the transistor stages, however I've already made the transistory bits and I can keep that in mind for the future, as there will be another itteration of this circuit.
     
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