Yes.... another 555 circuit topic (help requested)

[zappafan]

Hello and good day: I humbly require someone to check the included circuit. What happens is, when I apply power, the solenoid stays on instead of about 1sec. on and 1 sec. off.

I drew the circuit this way to assist layout and etch a circuit board. I DID use the 555 Times Utility to assist in doing the circuit, as shown in the attached screencap. The 555 used is an M8742 - LM555CN If you have any questions at all do not hesitate to ask. I need to get this done, built and installed on my machine.

Thank you very much in advance for any and all assistance.

[pebe]

Your problem is almost certainly because you have no suppression diode across the relay coil.

When pin3 of the 555 goes low, it suddenly turns off current through the relay coil. The result is that a large negative voltage spike is generated by the coil. As pin3 is next to the trigger pin2, the capacitive coupling between the two is sufficient to trigger the 555 again. So the relay appears to be permanently on. A suppression diode (also called a catching diode) fitted across the coil should clear the problem.

Fit the diode as close to the relay coil as possible, with its cathode to the pin3 end of the coil.

I hope that sorts out your problem.

[zappafan]

pebe: Thanks for the reply. I was wondering, after 20 views, if anyone would provide any clues whatsoever as to what the problem might be; maybe the circuit was too difficult? Ha Ha Ha..... just kidding.

I tried a 1N4001 diode, which did not work. I found a couple 1N4004 diodes, which I'll try next. I Googled for info on the relay.... thinking it might be a latching relay, but no luck on finding anything. Most all of the components I have are at least 20 years old, but they're new. I'm sure a few or the components could be considered vintage, and possibly hard to find "antiques." Anyway, I'm going to try a different relay, along with the different diode, and see what happens. I'll post the results later today. Again. Thanks!

[zappafan]

[quote="pebe"]Your problem is almost certainly because you have no suppression diode across the relay coil.

When pin3 of the 555 goes low, it suddenly turns off current through the relay coil. The result is that a large negative voltage spike is generated by the coil. As pin3 is next to the trigger pin2, the capacitive coupling between the two is sufficient to trigger the 555 again. So the relay appears to be permanently on. A suppression diode (also called a catching diode) fitted across the coil should clear the problem.

Fit the diode as close to the relay coil as possible, with its cathode to the pin3 end of the coil.

I hope that sorts out your problem.[/quote]

Well, I installed another relay, and tried a 1N4004 diode, but still having the same result. I also tried a different 555 but no luck. Maybe the wrong type of diode?

[pebe]

A fast diode like a 1N4148 would be best.

But first, make sure that is the problem by disconnecting the relay and measuring the voltage on pin3. It should rise and fall at 1sec intervals. If it does, then try the 1N4148.

If there is still a problem, then feed from pin3 via a 1N4001 in series with the relay and diode combination (anode to pin3). That will give even more isolation.

[zappafan]

[quote="pebe"]A fast diode like a 1N4148 would be best.

But first, make sure that is the problem by disconnecting the relay and measuring the voltage on pin3. It should rise and fall at 1sec intervals. If it does, then try the 1N4148.

If there is still a problem, then feed from pin3 via a 1N4001 in series with the relay and diode combination (anode to pin3). That will give even more isolation.[/quote]

Thank you, sir.... I'll see if I have a 4148 somewhere and let you know how things go. if I don't have one I'll have to check at Radio Hut here in town, but I won't hold my breath, as RS is mostly a TV and toy store now. My only other option is driving 60 miles to where I might find the diode, and I sure can't afford to do that right now. I'll keep you up to date as to what's happening.

[pebe]

In the hope that it may save you the 60miles trip, leave your existing (1N4004?) diode across the coil, as close to the coil as possible.

Then add the additional diode (1N4001 or 1N4004) in series with pin3, as I suggested. Fit the extra diode as close to pin3 as possible. You may get away with it.

An additional 'anti-spike' solution would be to fit a 1nF cap between pin1 & pin2 - again as close to the pins as possible.

Best of luck.

[zappafan]

[quote="pebe"]In the hope that it may save you the 60miles trip, leave your existing (1N4004?) diode across the coil, as close to the coil as possible.

Then add the additional diode (1N4001 or 1N4004) in series with pin3, as I suggested. Fit the extra diode as close to pin3 as possible. You may get away with it.

An additional 'anti-spike' solution would be to fit a 1nF cap between pin1 & pin2 - again as close to the pins as possible.

Best of luck.[/quote]

Hi, pebe: Well, we may have to back up a bit here as, after disconnecting the relay, I'm not getting a pulse out of the 555, instead getting a steady on state. My voltmeter is non-fuctional at the moment, so I improvised and used an analog meter out of a cassette tape player/recorder (using an appropriate dropping resistor to limit the voltage.) The "new" 555 I'm using is a 555D, which I believe shouldn't matter. The polarized cap is a 1Uf / 50 volt, and both resistors are 1 watt type. I've gone over the wiring twice and everything seems OK according to the schematic. In the meantime I'll try the 1nf if I have one. As always, thanks for your time.

[pebe]

The 555 contains a 'flip-flop'. It is triggered on (pin3 goes high) when pin2 goes below 1/3 of the supply rail. It goes off when pin6 goes above 2/3 of the supply rail. So if pin3 is always high and your connections are all correct, then it must be either the 2.2µF is short circuit (unlikely), or R1 or R2 is open circuit.

You can prove the 555 is OK by connecting pins 2 & 6 to pin8 to take them high. The output should then go low.

BTW, 1/4W is ample for R1 and R2.

[zappafan]

[quote="pebe"]The 555 contains a 'flip-flop'. It is triggered on (pin3 goes high) when pin2 goes below 1/3 of the supply rail. It goes off when pin6 goes above 2/3 of the supply rail. So if pin3 is always high and your connections are all correct, then it must be either the 2.2µF is short circuit (unlikely), or R1 or R2 is open circuit.

You can prove the 555 is OK by connecting pins 2 & 6 to pin8 to take them high. The output should then go low.

BTW, 1/4W is ample for R1 and R2.[/quote]

Thanks for the info, pebe. You are 4 hours ahead of me here in Wisconsin, USA, so you won't see this post for a while. By the way, I hope Scotland isn't going through the trials and tribulations that Ireland and others are going through.

OK.... I found a stash of 1N4148 signal diodes in my pile of components, and I replaced the Zener diode as per your instructions, and I also removed and replaced the 2.2uF polar cap, but I still have a constant ON state out of pin3. I haven't yet tried adding the 1nF cap because I don't have any on hand. [u]So, my idea for driving the relay as seen in my original post must be faulty[/u].

In that light, I've posted two new circuits. Graphic two is specifically for driving a relay, but it appears to be a monostable circuit (On/Off), however I need an astable circuit like shown in graphic One. I'll just have to build the circuit and see if it works, because it's different than the 555 Timer Utility (whoever developed that utility, thank you from myself and many others, I'm sure.)

I'll be building the circuit in the 1st graphic and see if it will drive a relay out of Pin 3, but I'll include the diode across the relay coil.

Possibly all the other viewers of my original post knew it wouldn't work and that's why they did not comment?

I'll keep you up to date on results. Have a good day.

[pebe]

Hi zappafan,

Fortunately, Scotland is not having the troubles that Northern Ireland had. Ireland’s problem was a fight about religions that dated back 400years! But Scotland’s troubles are due to a First Minister and a Deputy First Minister - whom I refer to as Mr Chatter and Mrs Yapp! They both suffer from ‘verbal diarrhoea’ and are hell bent on persuading voters that the country would be better off if it was an independent nation. If only……! Their outpourings so far are full of fallacies and lack any definitive statements. They just haven’t thought the whole thing through! But so much for politics…..

Coming back to the topic. Believe me, your original circuit was perfectly OK. I have built that circuit literally dozens of times without any problems. Did you connect pins 2 & 6 to pin 8 as I suggested. If you did and the output did not go low then you have a wiring fault or faulty 555. I know it’s a silly question but have you wired up the mirror image of the pinout (ie. pin1 is to the left of the notch when viewed from the top – not the underside).

Regarding your recent circuits, the top two are both astables – the diode gives asymmetry of the waveform, ie. making negative pulses or positive pulses. The bottom one needs to be driven by a square wave and is, in effect, just a switch.

If you want to pursue one of those circuits, use the top left one. But leave out the diode and the 4K7 resistor. As it stands its frequency will be too high. The product of the remaining resistor (in megohms) and the capacitor (in microfarads) must 1.4 for a one second on and off. So a 2.2µF cap and 680K resistor, or a 1µF cap and a 1.5M resistor in place of the 33K and 10nF will give you approximately the right time.

[zappafan]

[quote="pebe"]Hi zappafan,

Fortunately, Scotland is not having the troubles that Northern Ireland had. Ireland’s problem was a fight about religions that dated back 400years! But Scotland’s troubles are due to a First Minister and a Deputy First Minister - whom I refer to as Mr Chatter and Mrs Yapp! They both suffer from ‘verbal diarrhoea’ and are hell bent on persuading voters that the country would be better off if it was an independent nation. If only……! Their outpourings so far are full of fallacies and lack any definitive statements. They just haven’t thought the whole thing through! But so much for politics…..

Coming back to the topic. Believe me, your original circuit was perfectly OK. I have built that circuit literally dozens of times without any problems. Did you connect pins 2 & 6 to pin 8 as I suggested. If you did and the output did not go low then you have a wiring fault or faulty 555. I know it’s a silly question but have you wired up the mirror image of the pinout (ie. pin1 is to the left of the notch when viewed from the top – not the underside).

Regarding your recent circuits, the top two are both astables – the diode gives asymmetry of the waveform, ie: making negative pulses or positive pulses. The bottom one needs to be driven by a square wave and is, in effect, just a switch.

If you want to pursue one of those circuits, use the top left one. But leave out the diode and the 4K7 resistor. As it stands its frequency will be too high. The product of the remaining resistor (in megaohms) and the capacitor (in microfarads) must 1.4 for a one second on and off. So a 2.2µF cap and 680K resistor, or a 1µF cap and a 1.5M resistor in place of the 33K and 10nF will give you approximately the right time.[/quote]

Hi, pebe: As for the politics, I guess I don't understand why some countries turned themselves over to be run by a group of other people/countries.... basically giving up their sovereignty; although I know that some countries didn't give their people a choice in the matter.

OK... yes, I'll be using the one on the left in the graphic. I assume the 100n is still used? I have the new resistor value in 1/4watt, but It appears that I do not have the non-polar 2.2uF cap. Can I use a polarized cap? I have a bunch of monolithic caps, and quite a few ceramics I can go through, but I've yet to see anything close to a 2.2 in a ceramic (since they use numbers like 100, 101, 102, 103, etc.)

And, yes, I double-checked my wiring looking from the "bottom" of the circuit. I use Xara-X Pro for much of my graphic work, and it's easy to "flip" the diagram upside down. I'll post the new graphic when I get it done later tonight.

By the way, thanks for "doing the math" on the new components for me. Math was never my strong suit, which is why I became a welder and not a machinist ^_^ Oh, how I wish it was the other way around. And, I just might have a project that may be more of a challenge. Should I give you a hint?

As always, thanks for your time and assistance.

[pebe]

You will almost certainly need a polarized electrolytic or tantalum capacitor to get 2.2µF. Other types would be very large.

With all the 555 timer circuits I have built, I have never needed a decoupling capacitor (the 100nF) from pin5.

[zappafan]

[quote="pebe"]You will almost certainly need a polarized electrolytic or tantalum capacitor to get 2.2µF. Other types would be very large.

With all the 555 timer circuits I have built, I have never needed a decoupling capacitor (the 100nF) from pin5.[/quote]
Hello, pebe: Sorry it took so long to get back to you... kind of inconsiderate of me, even with the flu. Anyway, I thought you might be somewhat interested with checking out my web page and, since it appears you and I are the only ones who are concerned with my circuit issues, you could contact me through the website and we could go from there by email..... and use less bandwidth in the forum. [url]http://www.starfiretrailers.com[/url] It's your decision.

I have three pics I'd like to send of my prototype. I've made the changes, using a 2.2uf polar cap, and I've tried the circuit with and without the decoupling capacitor, and I get a strange result... no "output" on the on-board LED when I apply power, but when I remove the power I get a 'sound' from somewhere, [i]most likely the relay[/i]; but it only lasts a very short time so I can't source the location.

Contact me however you wish ad we'll go from there. Thanks, and I hope you had a pleasant weekend.

[sheldons]

if you add a transistor driver stage all your problems will go away......

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relay driver

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