LM555 for Air Cannon

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Thanks Ron; Right now I am using some $75 timing relays and thay only do the pulse not the hold. I would like to replace these and get the hold timing as well. I was thinking along the lines of a simpler circuit, IE one chip or a 555 and a RC circuit.
Andy
 
Hi Andy

Something that has not been mentioned or covered yet is the use of a PIC chip. The downside is you would need to program the little bugger. As to a single chip solution discrete there is the 556 which is two 555 timers on a single chip. You are still using two timers, just a single chip.

When you look at what you need it will pretty much always come down to a pair (two) of timers. One timer to deliver the desired pulse and the second timer to inhibit the first for a given time period.

Ron
 
Hi Andy

OK, looking back to your original post:

I would like to pulse the relay when someone steps on the mat for .1 to .5 seconds and then wait for 1 to 5 seconds before it can be triggered again.
Click to expand...

Keep in mind I am not a programmer type but I have done some very mild experimenting with PICAXE chips. These little micro controllers are cheap and pretty easy to program. Some salesman gave me some PICAXE chips to play around with a few years ago. So I dug out a little PICAXE 08M which is an 8 pin chip the same size as a 555 timer. I wrote a few lines of very simple code and loaded it on the chip. Actually 11 lines of a few words and it works fine. I can trigger an output pulse then ignore any triggers for a prescribed amount of time. The downside is that I can program the chip but once I do that the chip will run exactly what I told it to do. If I program a 200 milli-second pulse that is what I get but unlike a 555 the only way to change it is to reprogram the chip. With a few 555 timers you can shove a pot in and change the times. Know what I mean? But it can be done quite easily with a micro controller.

There are dozens of them out there in all flavors. Not being a uC type I stick to easy. When I retire and have time I'll mess with them more but for now PICAXE for Dummies is pretty good.

Ron
 
Ron; I am with you on the PICAXE, I have some PICs and the ones used in the PICAXE, but have not fould the time to play with them. If you use the A/D converters you should be able to read the pot values or posishoins and work that into the time delays.

Any PIC guys out thare??????

I am still going to try the analog solushoin but it may have less parts if done with a PIC.

Andy
Andy
 
Keeping me busy

Hi 4pyros,

here is another design using the dual timer IC NE556. The PCB design has become smaller.

Dimensions are now 61.2754X47.3075mm (2.4000X1.8625")

The design is not fully single sided and requires one wire jump.

I doubt that if using an MCU the part count will decrease. You will need a clean stabilized 5V power supply (the NE556 can be supplied with any voltage from 6 to 16V). You'll probably also need a stabilized reference voltage.

Making the time settings via A/D conversion you need a fixed value resistor and a trimpot for each channel as you need for the analog version. 8-pin MCUs don't have a built in A/D converter and I guess the pin count will be the same as using the 14 pin NE556.

IMO it's wasted engineer work to use an MCU for such a simple task.

If you're interested in the Eagle files you might download them (zipped) from the article.

Here are the screen shots of the latest version.

Regards

Boncuk
 

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Hi Andy

I have to agree with Boncuk in that the use of a uC really won't downsize things much if you look at it. Though the little PICAXE 08M will do pot input and has an A/D I don't know that it would be practical. I am guessing this is a Halloween thing and the clock is running down. Personally, I would run with Boncuk's 556 circuit, one chip and a few parts do it.

Ron
 
magnatro said:
hey bonuk the spacing on PCB is too low. i think it may cause shorting.
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Are you talking about component spacing or trace/pad spacing?

If your concern is component spacing - this is some kind of art not to be used by lumber jacks.

If it's trace/pad spacing: The spacing is big enough (0.3048mm between pads and traces) for everybody who knows how to solder properly.

Of course you'll have lots of shorts when you use a plumber's iron.

BTW, I'm Boncuk not "bonuk"
 
It might become a problem if mains is involved because of insulation distance.

In that case it's up to the user to modify the ground fill or omit it around the relay terminals. For short traces like in this example the load could take up to 8A without problems.

It does not matter if high or low current flows via the relay, voltage is what matters, starting to arc between traces and pads if it's high enough.

Nano technology is not necessary for a clean solder joint with relatively bulky pads.

The ground fill modification took me two minutes.

And yes, I'm using Eagle.
 

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I will try and solder up a prototype tonight. Boncuk can you tell me what D2 is for? Can you tell me the right resistors to ues with 2N3904 Transistors? Thanks Andy
 
4pyros said:
I will try and solder up a prototype tonight. Boncuk can you tell me what D2 is for? Can you tell me the right resistors to ues with 2N3904 Transistors? Thanks Andy
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Hi 4pyros,

I don't see D2 on the latest design. It was contained in the 2XNE555 design. D2 serves to discharge C5 rapidly when powering down the circuit.

The 2N3904 is about the same as a BC547. You might use the same value for the base resistor. Check for different pin connection of the 2N3904.

Top view of the BC547 is E-B-C, the 2N3904 has C-B-E. Rotate the transistor 180degrees and bend the base-pin to the opposite side for correct connection. (see attachment)

Regards

Boncuk
 

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Thanks I will let you know how it works out after I solder it UP. Andy
 
I had a very similar question (though for a completely different application) in this post.

After some simulating, I came up with a very similar circuit to what has been offered here. The key difference is that I used the output of the second timer to hold the trigger of the first timer high to prevent retriggering. I used a diode on that connection to prevent the first trigger from being pulled low when the second timer turned off.

I like the transistor method better -- it's just a good idea to separate the triggers from any potential sources of false inputs.

But if someone does not want or can't use a transistor to pull the first timer's reset pin low during the lockout phase, would sending the second timer's output via a diode to the first timer's trigger lead accomplish the same task?


Thanks.
 
I tryed to fishish one last night but ran out of time. Vary busy weekend. I dont have 6.8K ohm resistors, witich would be better to use for bass resistors for a 2N3904, 10K or 4.7K? Andy
 
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OK Thanks Ron. I am still trying to find the time to bild this thing but it may not be untill next week. Off hand whats the fomula for the bass resistors? Andy
 
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