Spurious triggering of 4013 flip-flop

One of my garden lamp circuits is shown here:

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But the CMOS 4013 flip-flop circuit suffers from occasional spurious triggering. Somehow it frequently gets activated overnight.

the very long wire (60 ft or so) carrying the high-going brief input signal. In places that runs alongside other wiring, some DC, some mains and that situation cannot be changed.

failing that an entirely new toggle circuit.

Terry, East Grinstead, UK

Reply to
Terry Pinnell
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rc filter and schmitt trigger?

Reply to
Johann Klammer

A cap to knock out noise is probably not enough you'd do better with some resistance before the cap (and maybe use more than 18K for the pull down input). Put a scope on that input with a X10 probe and crank up the scope gain and you may see AM radio....

Another approach may be to use more than one diode on the input to increase the voltage necessary.

Lower the impedance of the line driver if you can.

Increase the time for the high signal, then filter the hell out of it with a long time-constant R-C integrator.

Add a transistor on the input that requires a few milliamps to turn on

- that CMOS gate probably works with microamps

Look for something coincident with the problem - every time a furnace/AC or some other appliance is used, etc.. Filtering the noise at the source is usually more effective than at the device with the problem.

If you can scope it out you are ahead of the game since you know what you are trying to deal with. RF, switching transients, amplitude, duration, etc..

Create noise and see how sensitive it is. Line powered electric drills are noisy as a rule. I had one circuit that would respond to a spark igniter that was used to light the BBQ...

Does the ground run out to the signal source? You've got what may be a ground loop situation too. The 13V DC is sourced at the shed, is the ground return at the shed, and another ground at the signal source?

I can stick two copper rods in the ground here and measure a current that comes and goes with more than a 2V amplitude and will power a red led.... no power supply necessary.

good luck

Reply to
default

It's a very bad idea to trigger the clock input of a flip-flop from a slow-rise/fall-time signal. Add a Schmitt-trigger gate or a comparator with hysteresis, after the filter, before the clock.

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Reply to
Winfield Hill

And a grounded metal box. 4000 series logic has very wimpy output drive so is easily bashed around by external EMI.

Why not use a simple on/off switch, instead of an alternate action pushbutton?

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Reply to
John Larkin

Or design a more deliberate, slow, non-edge-sensitive circuit.

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Reply to
John Larkin

Many thanks for all those helpful suggestions, and especially to @default for such a comprehensive analysis. Much experimenting in prospect.

John: The input signal is from my 20 year old IR Remote Control project which uses a keypad to do stuff.

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I agree that a simple on/off switch would be more practical and eliminate the subject problem - but that would mean getting up from the sofa to toggle a switch!

Terry, East Grinstead, UK

Reply to
Terry Pinnell

Your input signal is 15V but your supply is only 13.3?

You are not meeting the abs max allowed clock fall time with that filter network

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(page 4 table 6.3)

I think you need some sort to shmitt trigger to clean that up, also then you can use a slower filter which should eat more noise.

could there be a ground loop that's causing the triggering?

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Reply to
Jasen Betts

due to

or

No, it means your remote control receiver would need to be modified to outp ut a constant level rather than a short pulse.

Or you could toss your remote in the can and buy one of the many garage doo r opener type devices from ebay for just a very few bucks. It might not wo rk any better, but at least you would have a project to work on.

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Reply to
gnuarm.deletethisbit

You don't show the arrangements for powering the 4013, and in particular, avoiding spikes on Vcc induced in the wire to the relay coil, and in the coil itself, both of which would be picking up interference. Although the transistor is off, there could be enough capacitance around given how little current the 4013 draws when its quiescent.

Sylvia.

Reply to
Sylvia Else

Put a 20K resistor in series with the input diode, right at the diode.

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Reply to
Robert Baer

a general idea: a debounce circuit (if controlled by a push button), followed by a latch on the receive side and a latch on the send side; the send-side latch is latched by a feedback signal from the second latch on the relay side (maybe with a bit of delay) to confirm that it's engaged. Use local power supplies, do the 60' run with shielded twisted pair and optocouplers to reject interference and ground loop probs.

sorta like:

Reply to
bitrex

Prolly want to edit that so the pulses go through the pair differential and not common-mode but it's a straightforward edit

Reply to
bitrex

Could you be suffering from condensation overnight in the shed? John

Reply to
jrwalliker

I always return to the house overnight ;-)

No evidence of condensation around the circuit.

Terry, East Grinstead, UK

Reply to
Terry Pinnell

I took it as understood that pins 14 and 7 were connected directly to +V and 0V respectively. My circuit problems would have been more serious otherwise ;-)

Do you mean something in addition to the two caps and usual protective diode?

Terry, East Grinstead, UK

Reply to
Terry Pinnell

Yes, it proved more convenient to use a separate PS in the shed. And the diode on the signal input lowers the voltage to about 14.4. I see that's well below the 20.5V specified in table 6.1 of your PDF.

Thanks, I'll take a close look at that, although it wouldn't explain the spurious triggering overnight?

Yes, that's been a repeated recommendation up-thread and I'm going to add one.

I guess so, although 0V is mains-earthed at both power supplies.

Terry, East Grinstead, UK

Reply to
Terry Pinnell

Thanks, will try that.

Terry, East Grinstead, UK

Reply to
Terry Pinnell

Since you have 2 supplies, I suggest use an Opto-coupler for isolation, use the two wires back to the loung (60') to pulse the opto diode.

Cheers

Reply to
Martin Riddle

A ha!

Reply to
bitrex

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