4017 prop. delay/connecting multiples outs

Discussion in 'General Electronics Chat' started by mxabeles, Apr 21, 2010.

  1. mxabeles

    Thread Starter Active Member

    Apr 25, 2009
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    hey yall I got 2 questions:
    1) In the official data sheet it shows how to cascade 4017s. Well, it works but at the end of the sequence (I got 3 4017s working) there is a pause of one clock pulse before restarting. Is there any way around this or just the way nature works?
    2) I tried having each decoded output turn on multiple leds. But it didn't work so well. Here is an example :

    output 1: turn on LED a, f, b
    output 2: turn on LED b, g, b
    output 3: turn on LED a, c, g
    output 4: turn on LED c, a, f

    So outputs are sharing LEDs. I thought this would not be a problem because only 1 output is high at a time (thinking about 4051s and how you can tie all outputs together and no issue). <snip>, any insight would be ground breaking.
    Thanks,
    M
     
    Last edited by a moderator: Apr 21, 2010
  2. mxabeles

    Thread Starter Active Member

    Apr 25, 2009
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    attached is the circuit i used to cascade the decade counters
     
  3. SgtWookie

    Expert

    Jul 17, 2007
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    Please keep in mind that this is a strictly G-rated forum.

    You need to use diodes on the 4017 outputs and transistor drivers for the LEDs, something like this:

    [​IMG]

    The 10k resistors limit the base current.
    The 1k resistors limit the LED current.
     
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  4. Ron H

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    Apr 14, 2005
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    You can use resistors to perform the OR function.
     
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  5. mxabeles

    Thread Starter Active Member

    Apr 25, 2009
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    hey cool thanks !

    I see that the two diodes (or resistors) make an or gate. Say I want 8 decoded outputs sharing a similar pin. To be specific, I want a decade counter to control the 3 inputs of 7HC183. I need 8 different combinations with the same three inputs. If i put diodes on all the outs from the 4017, could this work?
    Thanks
    M
     
  6. SgtWookie

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    Gee, I don't think that would work very well Ron.

    For example, you could have an LED with nine 10K Ohm resistors to outputs that are low, and one 10K resistor to an output that is high. So, you'd have 1.111..k to ground, and 10k to V+, so you'd get about V+ * 0.1 on the base of the transistor, and very low (if any) base current.

    Even with the diodes and 10k resistors, it's kind of pushing it. Ib would be about Ic/13 or so.
     
  7. SgtWookie

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    You need to post your circuit.

    I thought you were driving the LEDs directly.
     
  8. Ron H

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    Apr 14, 2005
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    I was only thinking of a 2 or 3 input OR. For example, with 3 inputs, base current would be around 900uA. Collector current would be 10mA or less, depending on the LED color.
    I agree that resistor ORing is not feasible for a wide-input OR, and that the diodes are the way to go.
     
  9. mxabeles

    Thread Starter Active Member

    Apr 25, 2009
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    a,b,c = s0,s1,s2 of 4051 for example

    output 1: none
    output 2: a
    output 3: b
    output 4: a b
    output 5: c
    output 6: a c
    output 7: b c
    output 8: a b c
    output 9: to RESET of 4017

    I believe this would cycle through outputs of 4051 from 1-8. Just wondering the OR gate can be more then 2 input.
     
  10. SgtWookie

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    Jul 17, 2007
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    Why don't you just use a binary up-counter?

    You'd eliminate all of the diodes, and you can control the LEDs directly.

    You don't even have to reset the counter, as the Q0 thru Q2 outputs are the same from 0-7 (b0000 to b0111) as they are from 8-15 (b1000 to b1111).
     
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  11. mxabeles

    Thread Starter Active Member

    Apr 25, 2009
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    hey cool, thanks! Yes, this makes more sense.
     
  12. mxabeles

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    Apr 25, 2009
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  13. SgtWookie

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    I don't know if you are considering a 4510 or a 4516.
    The 4516 is a binary up/down counter, and it will do the sequence you're looking for.
    The 4510 is a BCD up/down counter. It can be made to work, but you would need to have the reset connected to Q4 (either directly or thru and inverter; not sure at the moment) or else your count sequence would not be correct.
     
  14. mxabeles

    Thread Starter Active Member

    Apr 25, 2009
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    ok so i will get the 4516 at soon.
    I looked around the net but kind of confused. Are all the P1,P2,P3,P4 pins connected to ground?
     
  15. SgtWookie

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    Did you look at the timing diagram in the datasheet?

    All inputs to a CMOS device must be tied to either Vdd or GND, either directly or via a resistor.

    Unused outputs should be left disconnected.

    Never connect an output directly to Vdd or GND.
     
  16. mxabeles

    Thread Starter Active Member

    Apr 25, 2009
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    oh i didn't realize the p1,p2,p3,p4 were outputs. I thought they were inputs. They are some kind of preset?
    OK, so just leave them be i presume
    Thanks. For now though I think I'm going to keep it simple and mess around with 4017s, my LFSR circuits and the 4051 multiplexers. I think thats enough ICs for now.....
    Best,
    M
     
  17. SgtWookie

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    There's also the 4520 dual binary up-counter.
     
  18. Ron H

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    p1,p2,p3,p4 are inputs. Connect them to GND for your purpose.
     
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  19. mxabeles

    Thread Starter Active Member

    Apr 25, 2009
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    I am still struggling with cascading the 4017s.
    I used this model : http://images.elektroda.net/8_1178380869.gif

    I have a one step delay at the end of the chain. Is that considered the propogation delay, and if so is there any known way around this? Again, it is somewhat irrelevant for light display, but for audio work it is unacceptable.
    Thanks again,
    Max
     
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