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Momentary 4017 + 555

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adog111

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I'm working on a circuit with 21 outputs using 4017's, sequenced by a pushbutton. As the 'score' increments from output 20 to the 21st, I'd like to somehow activate a 555 (or similar) to rapidly clock the counters like a sequencer - to 'celebrate' reaching 21, until the counters are reset. I've got the basic circuit working pretty well - but can't get past square one the auto - sequencing part of the circuit. I thought I could use the 21st output to turn on a 555 to provide a clock input - not sure how to implement... Any ideas?
 

MikeMl

Well-Known Member
Most Helpful Member
Post a circuit of what you have now. Highlight the output that you want to use to modify the sequence.
 

adog111

New Member
Attached is a sketch of the schematic. Since I need 20 indicators, I thought I would use the 21st output in sequence - Q3 from the 3rd counter to power up the 555. You can see this is based on the cascade diagram in the 4017 datasheet - works quite well - however when trying to integrate the 555 into the circuit - I don't know how to handle the the reset on the first counter. Also, as soon as another clock cycle occurs, Q3 will go low, removing power from the 555. Clearly, I'm not on the right track with this idea on how to switch from a single step clock to an astable 555 output... I'm learning as I go here, so any ideas would be appreciated.
 

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adog111

New Member
4017 outputs ON when in RESET

Thanks for the link to the 555 application circuits - i was able to find one that fit and it's working perfectly. However, as my circuit has 'aged', it has developed an annoying feature - when the scoreboard is actively counting, ie., NOT in a reset mode, it's working fine with one LED on and all others dark. When RESET is triggered, all the LED's come on at a very low, but perceptible level, then go out as the clock is triggered. Any ideas what might have gone wrong here?
 

adog111

New Member
The basic circuit is 3 - 4017's cascaded to get 21 outputs, wired up just like the 4017 datasheet says to do. I have the IC's powered by a +5 volt source, with the outputs to the LEDs wired to the base of a 3904 transistor, with the collector seeing 10v and the emitter connected to a 100 ohm resistor to ground. The timer portion of the circuit is inconsequential. If I isolate that part of the circuit, I still get the low level LED illumination. The circuit is powered by 8 AA NiMh batteries, with a 5 volt regulator, and the 10volts wired directly to the transistor collectors. All share a common ground. I don't have a legible schematic - I'll clean one up and post. I have built two identical circuits like this - both behave the same way, with low level LED illumination when reset, fine otherwise.
 

4pyros

Well-Known Member
Most Helpful Member
with the outputs to the LEDs wired to the base of a 3904 transistor, with the collector seeing 10v and the emitter connected to a 100 ohm resistor to ground.
Are you using the transistors to drive the LEDs?
Put the 100 ohm resister on the power side (collector) to keep the grounds at the same potentials.
 

MrDEB

Well-Known Member
reason for 4081?

Just cascade the 4017s then using a 556 set up with one as a mono stable for incrementing up to 20
the second part of the 556 set up as a astable. Using an NPN transistor to switch the clock input to the first 4017.
When the last LED comes on it switches the input to the first 4017 at a rapid desired rate.
Don't know why you have a 100 ohm resistor to ground. As pointed out it should be on the V+ side but why is it there?
I must have missed something
 

adog111

New Member
Thanks 4pyros - moving the resistor solved the problem. the 100 ohm resistor is intended to limit the current thru the LEDs. I blew several out trying to get them bright... Circuit is working nicely. Thanks guys.
 
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