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Blinking Halloween Eyes?


JakeElwood
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Hi, I have a small Halloween project. The final goal is to have several pairs of LEDs (cut from a Christmas light chain) and have each pair wired to its own flasher circuit. The intervals wouldn't have to be random, but the timing of each flashing pair should be different. A simple timer should do the trick. One pair might have 1.5 seconds on, 200ms off, and the other pairs would have slightly different timing. You then hide the pairs of LEDs in the bushes and voila, blinking eyes. I'm only familiar with basic electronic components so until I get beyond the "beginner electronics hobbyist" phase a lot of the terminology is going over my head. Can I fake this by wiring fluorescent starters into each circuit or using those flasher buttons that you put in a light socket?
Thanks,
Jon

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I guess the control circuit could be at 5V or whatever PICs run with, and a relay on that circuit would control the house current? The goal would be to have one controller (or several if necessary) creating the individual blinking patterns on a separate circuit with house current (either attached lamps or separate outlets for each flasher circuit). Or the whole thing could be 115V but that might make it tricker to work with and test.

I've heard of high-intensity LEDs and they might be enough, but I'd like the option of flashing something brighter if the LEDs (hacked Christmas light chains etc.) don't do the trick.

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LEDs, even the ones from a 115VAC strings, are 1.7VDC to 3.4VDC, depending on color.  So you will need a low voltage power supply anyway.  Here is a timer that could work.  The long period is 2.5 to 60 seconds and short pulse is 0.5 to 5 seconds.  These can be changed to your time range by replacing several components.  You would need one timer for each pair of eyes.  The output is a relay that could be used to switch low voltage DC or 115VAC lights.
http://www.arcade-electronics.com/detail.aspx?ID=17763

Ken

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Great, thanks for the link! It would be my first soldering project but at $5 I think I can chance it. My application is unusual since my "pulse" time is actually the longest part of the cycle. With this board the maximum pulse is 5 seconds and the minimum pause is 2.5 seconds, which is too long for a blink, so I'll probably be replacing a pot or two. The other option is to use the unit as-is and add a component to reverse the pulses and pauses, if such a component exists.

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Well you've talked me out of the house current idea since the brightness at 5v is fine for this job. I have a simple circuit (from a starter kit) using a 556 chip that blinks an LED and the timing can be tweaked by changing a capacitor. Now I need to blink 2 LEDs at once (wire in parallel each with its own resistor?), get it to blink off instead of on (transistor NOT gate?), and then get several pairs going at different rates. Will each pair require its own chip? I'll post a schematic if I can find a nice online utility for drawing one up.
Jon

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Hello
  You can make a square wave oscillator with two npn transistors, two capacitors, four transistors, two leds, and a nine volt battery. The only other part you would need is a battery clip, and if you want to get fancy a project board. Thats an old timer project. they use to take a peace of wood and drive copper nails to were they wanted to solder the components to and wire in the rest. You don't need a ic to flash leds.
                                         gogo

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Ken - Thanks for the express PCB link, I'll see what I can draw up.
Gogo - I have all those parts plus the battery clip and breadboard so I'm good to go, except that I have almost no clue as to how those parts would go together. I do know that a pair of LEDs can be wired in series with the appropriate resistor, transistors can be used as switches, and capacitors will affect the timing. Looks like it's time for some experimentation, but I'm told that I can fry transistors (and LEDs) if I hook them up wrong. Good thing they're cheap.

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I tried the circuit and it gave a fade-in pulse at about 120 Hz, but I was using a 220 cap instead of the 330 in your diagram so maybe that was part of the problem. No worries, I have about four other schematics I've found online that I can try so I'm sure I can sort it out (except for the random blink intervals but that can wait).

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I tried the circuit and it gave a fade-in pulse at about 120 Hz, but I was using a 220 cap instead of the 330 in your diagram so maybe that was part of the problem. No worries, I have about four other schematics I've found online that I can try so I'm sure I can sort it out (except for the random blink intervals but that can wait).
Was that my circuit you built?

The frequency should have been about 0.5Hz if assembled correctly.

Are you sure you've not used a 220nF capacitor or soldered it in the wrong way round?

The frequency is roughly equal to the following formula:
F = 1.1/(C1

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Hero - Right, that was your circuit I built. I meant 120 bpm, which would be 0.5 Hz, my mistake. It looks like it was working correctly, even with the 220 resistor. I was changing out all the components to experiment, I hope I didn't damage the 556. I was also careful to match the 556 pin numbers with the 555 pin numbers in your schematic.

This is to make a blinker, not a fader, right? The end result should have the LED pair blinking on and off with a square pulse, about 95% on and 5% off (or less), at 1-3 second intervals (variable intervals is the next project).

I can run six independent oscillators on a 74HC14 chip? Is there a buying guide for ICs and PICs? There seem to be several that I could use and I'm not clear on which I should get. I'm planning on getting a few extra 555 or 556 chips since they seem pretty useful.

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By the way the R2 in the previous schematic should have been 47R, with 330R it 3V it would be too dim.

I thought you wanted a fader?

A blinker is much simpler.

The pinout for the 74HC14 is on the datasheet which can be found using Google.

If you want two LEDs then use a >6V power supply and put tw LEDs in series.

For 6V and two LEDs R2 should be 120R.

Note that the maximum supply voltage for the 74HC14 is 6V.


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Thanks - I'll give it a try. I'm sure I can find the pinouts for the 4HC14 - I just don't know how to read the schematic yet (which side of the triangle figure corresponds to which pin). Input, output, power and ground make sense from the figure but then there's triggers, thresholds, reset etc.

I assume that varying the pulse width is just a matter of changing out resistors and capacitors. As far as the LED pair goes my power supply is 9V with a voltage regulator that brings it to 4.5V so I'd need to mess with that to get 6V. Time for more reading, more theory. Anyway thanks again!

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Thanks - I'll give it a try. I'm sure I can find the pinouts for the 4HC14 - I just don't know how to read the schematic yet (which side of the triangle figure corresponds to which pin). Input, output, power and ground make sense from the figure but then there's triggers, thresholds, reset etc.

As I've said above, it's on the datasheet, as you appear to have forgotten how to use Google, here it is.

http://tamarisco.datsi.fi.upm.es/ASIGNATURAS/FMI/COMPONENTES/MM74HC14_(InvSchmitt).pdf


I assume that varying the pulse width is just a matter of changing out resistors and capacitors. As far as the LED pair goes my power supply is 9V with a voltage regulator that brings it to 4.5V so I'd need to mess with that to get 6V. Time for more reading, more theory. Anyway thanks again!


You only need to change the value of R2, for 4.5V and two LEDs in series use 150R.

Heck way not use a flashing LED?

Just connect it in series with a non-flashing LEd and a  suitable series resisto and off you go. Each flaching LED will have a slightly different flash rate so they'll be slighlty out of phase and will all end up turning on and off at totally different times.
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As I've said above, it's on the datasheet, as you appear to have forgotten how to use Google, here it is.


Knock it off. I'm going from a $50 kids' starter kit to reading this stuff, it takes time.

It looks like the 4HC14 has six identical oscillators (schmitt triggers) any one of which can be wired like in your schematic. It's still not clear how these pins relate to the pins on a 555 (threshold, trigger, reset etc.) but I guess it doesn't matter as long as it works.

I've thought about using flashing LEDs but I don't think that will give the right pulse waveform. Making strobes seems to be the default for many blinker circuits - making a light blink briefly OFF instead of ON seems less common. Still pretty simple though, I'll get it. Thanks again.
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It looks like the 4HC14 has six identical oscillators (schmitt triggers) any one of which can be wired like in your schematic.

I think I can see where you went wrong: it's the 74HC14.

It's still not clear how these pins relate to the pins on a 555 (threshold, trigger, reset etc.) but I guess it doesn't matter as long as it works.
They don't, it's a totally different circuit which has nothing to do with the 555.

You can use either the 555 or the 74HC14s.

As you need 12, using two 74HC14s will work out cheaper than six 556s but it's up to you, it depends on what parts you have available.

I've thought about using flashing LEDs but I don't think that will give the right pulse waveform. Making strobes seems to be the default for many blinker circuits - making a light blink briefly OFF instead of ON seems less common. Still pretty simple though, I'll get it. Thanks again.

Oh, I missed that, my circuit will blink on-off 50%-50% duty cycle.

You want on 95%, off 5% don't you?

Then the schematics will need a coule of modifications.

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