Re: 4017 Counter skips under load

Joerg <notthisjoergsch@xxxxxxxxxxxxxxxxxxxxx> wrote in news:laAii.8019
$Rw1.3242@xxxxxxxxxxxxxxxxxxxxxxxxxx:

me wrote:

Joerg <notthisjoergsch@xxxxxxxxxxxxxxxxxxxxx> wrote in
news:9_zii.8017$Rw1.4043@xxxxxxxxxxxxxxxxxxxxxxxxxx:


David L. Jones wrote:


On Jul 4, 6:50 am, jcargile2...@xxxxxxxxx wrote:


On Jul 3, 1:24 pm, Joerg <notthisjoerg...@xxxxxxxxxxxxxxxxxxxxx>
wrote:





jcargile2...@xxxxxxxxx wrote:


On Jul 2, 3:24 pm, "David L. Jones" <altz...@xxxxxxxxx> wrote:

On Jul 3, 7:11 am, jcargile2...@xxxxxxxxx wrote:

I have a fairly simple circuit that consists of a 4017 decade
counter and nine relay/LED combinations. The relays are very
small and the circuit operates just fine with no load, or when I
connect an LED to the relay output. But when I try to operate
the circuit under load (it is being used to fire nichrome
ignitors), then the counter simply skips the loaded relay and
moves right to the next output. So if I send the counter a
series of 5 clock pulses, and put a load on the relay attached
to
output 3, then the count goes 1,2,4,5,6. The final count ends
up
being one off, so it's almost like the output in question
doesn't
exist. What I don't understand is why this is happening, since
the relay is what bears the load, not the 4017. Shouldn't the
output requirement on the counter be the same regardless of what
the relay is switching?

Yes, it should be, but only if you have used proper circuit
physical circuit layout techniques to ensure that there is no
ground or power bounce.
Think "star grounding" and power decoupling.
Very common trap for young players.

Dave.

I installed the final power setup (on the tests I just had the
board jumpered onto the power supply) and now it will fire the
ignitors. The problem is that the counter is now behaving
irratically. It will skip several counts when receiving a clock
pulse and will jump around with the slightest change in ground
(even connecting a single lead from the multimeter to any point on
ground advances the count). I've tried several different caps
(.01-10 uF) connected directly to the power leads of the 4017 with
no luck. All of the info I can find on decoupling keeps talking
about selecting the capacitor based on frequency. But I'm only
sending a single pulse of about 25 ns every 10-20 seconds. Does
this mean I can use a larger cap? I'm seriously freaking out at
this point cause I only have 24 hours to get this working. Thanks
for the help!

How on earth do you get a 25nsec pulse out of a CD4017? That's like
clocking a moped at 100mph.

Anyhow, since things seem to become desperate over there I can only
suggest to build it up again on an experimental board that has a
ground plane. And no, you do not have to select decoupling caps
based on frequency. A 0.1uF plus a nice 10uF electrolytic should
do,
more if your power supply is wimpy.

Can you post schematic plus photo?

--
Regards, Joerg

http://www.analogconsultants.com-Hide quoted text -

- Show quoted text -

Sorry, I mistyped. The clock pulse coming into the 4017 from the PC
parallel port is 25 ms in length.


Ah, the alarm bells start ringing right there, no pun intended.
You probably have ringing on your clock line from the PC. Keep the
lead from the parallel port as short as possible.
Are you able to view the signal with an oscilloscope?

Classic problem with PC parallel port driven equipment.


Good point. It could also be relay current spikes getting into that
clock line. Might be worth using a coax. And no long lines of several
feet or you get riniging like crazy on it.



Another problem might be the clock. What are you using for the clock
signal that you can send five pulses?


AFAIU the OP uses a pin on the parallel port of a PC for that. Which
makes me wonder about the levels. I think the parallel port is TTL and
if he runs the 4017 at 5V it'll be quite sluggish and have weak outputs.


True enough, and I've seen some parallel ports that were marginal for TTL
level highs.

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Relevant Pages

  • Re: 4017 Counter skips under load
    ... small and the circuit operates just fine with no load, ... connect an LED to the relay output. ... It will skip several counts when receiving a clock ... lead from the parallel port as short as possible. ...
    (sci.electronics.design)
  • Re: 4017 Counter skips under load
    ... But when I try to operate the circuit under load ... skips the loaded relay and moves right to the next output. ... Think "star grounding" and power decoupling. ... lead from the parallel port as short as possible. ...
    (sci.electronics.design)
  • Re: 4017 Counter skips under load
    ... But when I try to operate the circuit under load ... skips the loaded relay and moves right to the next output. ... Think "star grounding" and power decoupling. ... lead from the parallel port as short as possible. ...
    (sci.electronics.design)
  • Re: 4017 Counter skips under load
    ... But when I try to operate the circuit under load ... skips the loaded relay and moves right to the next output. ... with the slightest change in ground (even connecting a single lead ... lead from the parallel port as short as possible. ...
    (sci.electronics.design)
  • Re: 4017 Counter skips under load
    ... But when I try to operate the circuit under load ... skips the loaded relay and moves right to the next output. ... lead from the parallel port as short as possible. ...
    (sci.electronics.design)
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