Alright people!

Did I mention I wanted this to be simple? All the cool tech you guys are talking about is really neat and all, but is it necessary? All I want is a randomly blinking light. It doesn't need to be complicated. Can we get back to the dual 556 idea and see what we can do?

-topsoil

 

I can have a faily random sequence with 2-4 555's. It would be something like LEDs, 555s, Flashers, and Light Chasers Chapter 8 From Four, Twenty.

 

Like I've said earlier, I'm not an electronics engineer, but I think I understand what I want here. I've done some reading and this is the concept.

take 2 556sICs (or 4 555s) and hook them up as LED flashers with different rates. Add a couple of logic gates. maybe a pair of AND gates to see if any two or three of the 555 outputs are HIGH and if so light the LED.

If the logic gates could be set to only light the LED if three of the 555 outputs are HIGH and we play around with the rates on the 555s I think the actual flashing of the LED would be random enough.

May be adding i more 555 after the logic would allow us to set a duration for the illumination of the LED.

I'm not sure of the proper way to show logic output in text but maybe you can read this...

outputs from 555s >>> Output of LED

1 1 1 1 >>>>>>>>> 0
0 1 1 1 >>>>>>>>> 1
0 0 1 1 >>>>>>>>> 0
1 0 1 1 >>>>>>>>> 1
1 1 0 1 >>>>>>>>> 1

etc

You get the picture. If the rate of each 555 is different the LED should flash at a pseudo-random rate, yes? and if the fastest 555 is cycling at 2 seconds the longest interval would be maybe 8 seconds? the shortest 3? those are guesses. Anyone out there have a good simulator?

-topsoil

 

You don't even need logic gates. If you look at the schematic I referred you to the LEDs and resistors go directly between the outputs of the 555's.

How many LEDs are you wanting? I assume two LEDs tied together to look like a pair of eyes. I do something similar during Halloween, I've build a bunch of simple 555 circuits (one 555 per circuit) with a pair of LEDs. I deliberately used a random pile of resistors, so no two are alike. The bushes have eyes that are on for awhile, then go out. I call them bush goblins.

If you want a single pair of LEDs 2 555's (or the dual 555 version, the 556) will work. If you want more a few more 555's will do that too.

You can control the percentage of time it is on pretty easily, and the average duration. Being random it will only be an average. What are the parameters you are looking form?

 

Well It will only need one light, studies show that two lights don't work as well. It has to do with the way predators hunt at night. They try not to be seen and part of that is to keep their eye's from reflecting light too much. Kinda like hunting from down wind. Evolution has made them pretty sneaky. Deer on the other hand will jump and run if they see a glimpse of light that they think is reflected from a predators eye. If they see two points of light they interpret it as another prey animal, and don't get spooked off. (or so the experts say)

So...

Only one light, pretty bright, and it needs to flash at a random rate between 2 an 10 seconds (maybe up to 30) and only be illuminated for 1/2 a second. If the illumination could be randomized, form 1/10 to 1 second that would be great, but not really necessary.

-topsoil

 

You willing to buy a protoboard and cobble together a circuit to meet your specifications (in other words, build a prototype and tweak it)?

OK, one LED, lets assume a simple power supply, 4X AA batteries at 6V. Battery holders are available from Radio Shack, as are TLC555 CMOS 555's. To increase the apparent randomness I'm going to use 4 of them and one red LED.

I'll have an approximate schematic with more details posted within 24 hours. It may not be as simple as you would like (you are replacing hardware for software), but I can give you some ideas for shortcuts to remove components.

 

OK, here is what I envision...

You could eliminate U1 and U3 (and the associated circuitry). It would be bit more obvious, and the resistors would need tweaked to compensate.

I would dearly love to replace CR1 and CR4 with 1µF tantalum's (Radio Shack sells them) and replace R2 and R5 with 7.5MΩ resistors and R1 and R4 with 2.7MΩ and 3.3MΩ respectively. It would increase battery life a bit, but the resistors can be hard to acquire.

This circuit is made for very long battery life (4X D cells will be good for almost a year, maybe more). The LED is meant to be dim, you can reduce R13 to very low values (10Ω would work), it will still be dim but noticeably brighter.

This has come up before at this site, but random isn't simple. Actually it is durn complex. Think about it, electronics can do repetitious forever.

 

This has come up before at this site, but random isn't simple. Actually it is durn complex. Think about it, electronics can do repetitious forever.

This is very true. Which is why I suggest an 8 pin uC (Cost: <$2) to do the entire task, though the $35 programmer bumps the price up a bit for a one off project.

Less to go wrong, better battery life if sleep mode is used between flashes, 3 components total (IC, Resistor, LED), etc.

 

Going to need a way to turn all of this stuff off during daylight, too - otherwise, the batteries will get run down a lot more quickly.

 

This very similar to long duration series of flashers, though it is four of them. The LED is choked back quite a bit. I put the battery life for AA at around 1-2 weeks. I suspect it with the D cells it is good for a minimum of 6 months, probably a lot more, with continuous use. Use will tell.

 

This is very true. Which is why I suggest an 8 pin uC (Cost: <$2) to do the entire task, though the $35 programmer bumps the price up a bit for a one off project.

I appreciate the simpleness of the uC design and the cost isn't too bad really. It's the time factor that gets to be a problem. Soldering I know how to do. programing... not so much. I'm sure it's simple but I'm equally sure there is a learning curve that will need to be addressed. I don't really have time to learn a new technical skill right now. especially one that see no real use for in my immediate future.

-topsoil

 

I was thinking 4 C batteries, so maybe 6mo or so between battery changes? Two batteries would be better, but I'll work with four.

What would the cost in battery life if the LED was to flash brighter? and is it a simple change? I'll need to see how bright this version is first of course. it might be just fine.

I've got a prototyping board somewhere I'll dig it up and start building as soon as I can dig up the parts.

thanks

-topsoil

 

Truth, I don't know. This is brand new design for me. I know it will work, I don't know how well it will work.

I have some experience with simple long term flashers. Look at the projects with long duration in the name at this link. The average is 1 month off two AAA batteries, which isn't bad.

The 555 Projects

The design I drew for you doesn't have to have R13, the CMOS chips will limit the current to the LED, it is both a curse and a feature. It will shorten the battery life. Everything will either shorten or lengthen the battery life. I'd go for anything that would lengthen it first, such as the component changes I mention on post #27.

The µC is a good option. Maybe one of the guys will step up with a programmed chip if you pay their costs, it is a steep learning curve to do from scratch and there are specialized tools involved. There is no doubt the finished cost (minus tools) is much cheaper.

If you decide to build this shop for the parts. I try to source Radio Shack, but the finished project will be X4 or more expensive, but you don't have to pay shipping.

If you have questions put them on this thread. If I miss it just PM me to remind me this thread is here Most of the guys do not mind helping beginners.

I've barely started down the road of microcontrollers. I just bought an Arduino (a specific brand name) simple development kit. I won't be functional on it for months, maybe years. It may not be the best, but the kit is pretty simple overall. BG Micro is a walk business in for me, as it is local. They have a great dane who helps mind the store, we're buddies.

http://www.bgmicro.com/search.aspx?find=arduino

 

Bill, that circuit schematic you drew up, Do you have a component list for it. I can copy it out my self but a list would be nice.

-topsoil

 

Bill, that circuit schematic you drew up, Do you have a component list for it. I can copy it out my self but a list would be nice.

-topsoil

Tain't hard, just have to go through the schematic.

Designation(s) ..Qty .Description
U1-4..............4...CMOS 555, Radio Shack TLC555 or 7555
CR1-6.............6...Any General Purpose Diode, Radio Shack 1N914 10 pack
D1................1...Red LED
R1,R8.............2...270KΩ ¼W 5% Resistor
R2,R5,R7,R10......4...1MΩ ¼W 5% Resistor
R3,R6,R9,R12......4...300KΩ ¼W 5% Resistor
R4,R11.......,....2...270KΩ ¼W 5% Resistor
R13.........,...,.1...470Ω ¼W 5% Resistor
C1,C4,C7,C10......4...10µF electrolytic 25V or greater
C2,C5,C8,C11,C14..5...0.1µ capacitor
C3,C6,C9,C12,C13..5...220µF electrolytic 25V or greater

Alternate Parts List for longer battery life.
Designation(s) ..Qty..Description
U1-4............,.4...CMOS 555, Radio Shack TLC555 or 7555
CR1-6.............6...Any General Purpose Diode, Radio Shack 1N914 10 pack
D1................1...Red LED
R1................1...2.7MΩ ¼W 5% Resistor
R2,R5.............2...10MΩ ¼W 5% Resistor
R3,R6,R9,R12......4...10Ω ¼W 5% Resistor
R4................1...3.0MΩ ¼W 5% Resistor
R7,R10......... ..2...1MΩ ¼W 5% Resistor
R8................1...270KΩ ¼W 5% Resistor
R11...............1...300KΩ ¼W 5% Resistor
R13...........,...1...470Ω ¼W 5% Resistor
C1,C4.............2...1µF Tantalium Capacitor (Radio Shack carries it)
C7,C10............2...10µF electrolytic 25V or greater
C2,C5,C8,C11,C14..5...0.1µ capacitor
C3,C6,C9,C12,C13..5...220µF electrolytic 25V or greater

The resistors are not critical, you can have some variation on them as long as they are in the ballpark.

 

thanks for the list

-top

 

Let me know how it goes, I'll be following with interest. You see the forums new Flea Market forum? I might be able to help with some of the parts.