4017 Counter skips under load

Looks like power supply spikes, sub-optimal decoupling or a substrate diode gets hit. Time to crack out the storage scope, I'd say. Hang it onto VCC of the 4017, then to the pins.

--
Regards, Joerg

http://www.analogconsultants.com

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

Sorry, I mistyped. The clock pulse coming into the 4017 from the PC parallel port is 25 ms in length. The counter then activates the next relay in sequence and the output stays active for 10-20 seconds before moving on to the next firing cue. I'll post a printout of the circuit design when I get home in a couple hours. I'm using a pretty good sized power supply, and I've tried other power sources as well with the same results. Should I be doing some sort of decoupling where the power enters the board as well? I noticed that the parallel port interface card that I'm using has some sort of diode/cap combination where the power enters the board. Would this help even things out further?

--
25ns is seriously pushing it.  Increase your clock pulse width,
make sure the driver is low-Z when its output is either low or high,
and keep its output as close to the 4017 as possible. 

Also, if you\'re not already doing it, use a separate supply for your
igniters and make sure you\'ve got a catch diode across the relay
coils.

If you can\'t use a separate supply for your igniters, then you\'ll
need to decouple the counter and its circuitry from the supply wit a
diode and a big capacitor.  

can you post a schematic of your circuit somewhere?

Alt.binaries.schematics.electronic will work, or any where you can
post it and supply a link to.

Yes - Rich Sez: You Can't Overcapacitate Power and Ground Planes. :-) (Unless you've got some temperamental LDO regulator or some such... ;-) )

Do the relays have reverse diodes or RC snubbers across the coils? If not, put them there. You say the relays are sensitive enough to be driven by a

4017 - small-signal diodes like 1N914 or 1N414x would work fine.

Depending on what you're switching, it might not hurt to put another snubber at the relay contacts; this would probably be RC, depending.

Good Luck! Rich

Ok, I might not be there at that time but others will be. As Rich said, mind the relays. I would not drive them directly from the chip, it does not like inductive loads and their spikes. At the least place some kind of buffer in between. The CD40106 for example.

If the power supply is clean you don't need much filtering onto the board if the leads are not longer than a few inches. But the CD4017 should be grounded and there should be a 0.1uF from its VDD pins straight to the ground plane.

If you post, maybe also include a photo. That can help a lot. For schematics a scanned hand sketch is fine.

--
Regards, Joerg

http://www.analogconsultants.com

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.

Dave.

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.

--
Regards, Joerg

http://www.analogconsultants.com

Joerg wrote in news:9_zii.8017$ snipped-for-privacy@newssvr25.news.prodigy.net:

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

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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.

--
Regards, Joerg

http://www.analogconsultants.com

Unfortunately I don't have access to a scope. This is the kit that I'm using. The board itself is plugged directly into the parallel port. I then have leads soldered on to the board at the resistors so that I get a clean 12 volt signal from the parallel port. From there, that signal is run via ethernet cable to the firing controllers. In my initial tests, this setup worked fine with just an LED as the load. Because of safety reasons, I can't have the laptop and thus myself any closer to the controllers themselves.

Joerg wrote in news:laAii.8019 $ snipped-for-privacy@newssvr25.news.prodigy.net:

to

up

doesn't

do,

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

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Ah, a picture tells a thousand words.

The board should work just fine *if* you power your load from an entirely separate and *floating* power supply relative to the plugpack or power supply which powers the board. You've said the board works just fine with an LED load, so obviously something is amiss with the power supply wiring for the load.

Dave.

That looks like something very different. No 4017 but a ULN2803 driver.

Sure you are getting 12V from the parallel port? I never saw one that did that.

--
Regards, Joerg

http://www.analogconsultants.com

(snip)

And you won't - they are TTL. But the 2803 et al are TTL-compatible input.

Note the data sheet at

shows a solenoid driver config on p1.

If you are using the same supply for the 4017/relay circuit and for the igniters, do this:

+V -----+----------> To igniters through relay contacts |a [Diode] | +----------> To your 4017/relay circuit Vcc |+ [470 uF] +---> To your 4017/relay circuit gnd | | Gnd ----+------+---> To igniters ground

The idea is to stabilize the supply voltage to the 4017/relay circuit. Without the diode and cap, when the igniter fires the voltage to the 4017 suddenly sags.

At the 4017 circuit board, add a .01 cap across the supply input.

Ed

That is a parallel port interface kit that I bought some time ago and use for any applications where computer control is needed. It is completely different from the boards that use the 4017. I will post pics in the morning when I have enough good like to get a detailed picture. As for the parallel board, the 2803 went out, so I replaced it with an NTE 2018. I'm told that they are an identical match, both

8 channel darlington arrays. Am I wrong in assuming that if the on- board relays are rated for 12 volts, as is the power supply, that the output from the 2018 is also 12 volts?