Dimming 'Random' LED's

"Any ... further questions" - Yes! - why not use a microcontroller? - it would be a lot easier .

I don't know code

Buy the blinking LEDs. They are available at different colors and blinking rates.

Blinking rate is fixed and fast.

The requirement is dim for sometime not annoying to sight; that is slowly [probably adjustable in time and brightness]

Slow blinking/dimming rates (up to 1cycle/5 secs) are available.

so how does this guy get GA when he did not read the question...OP does NOT want blinking LED's...dimming from bright to partial

Blinking/Flashing/Dimming LEDs are all in one category...too general in classification.

When you say 'random'. do you really mean random, or just 'not obviously synchronized'?

It is relatively straightforward to make an oscillator/multivibrator whose output is divided to get an appropriately low output frequency, and use that output to run a sine-wave approximator. I did just that using 4000 series cmos chips about 35 years ago... If you want more info, send me a message...

Dick

The simplest method I know is to have a DC supply, say 12 volts and feed a capacitor with a resistor across + & -, place a LED across each cap, watch out for polarity of both caps and diodes. It should flash if I remember correctly.....

Using different value caps and resistors will change the frequency and the length of blink. If the blink is too short/bright, add another resistor in the leg of the LED.....

I haven't done this for years so I cannot give you values, but you will need Electrolytics......just play around.....

If I was doing it today I would use a PICAXE chip with as many output pins as you want to drive LED chains, transistors for large numbers of LEDs, and base my code on one of the many free example programs that are available.

As the PICAXE uses a simple form of the BASIC program language, you should be up and running within 2 days of investing maybe $15 for EVERYTHING!!! AND having a ball and changing the original program to suit yourself and the family and making yourself BASICally CLEVERER at the same time, a "win win" situation.....

All needed manuals and software are free to download, you need no "programmer" as a simple Com port or USB cable/adapter does the job, but DO buy the one from Rev-Ed as some others do not always work properly....

Go here:-

http://www.rev-ed.co.uk/

http://www.picaxeforum.co.uk/forum.php

http://www.picaxe.com/Getting-Started/PICAXE-Manuals/

Andy,

you made that sound like fun.

for $15 I'll have to give this a try as well.

Plus Postage, but the suppliers are everywhere so it should not be excessive......Look here for your local supplier:-

http://letsmakerobots.com/node/213

GA Andy, if you want simple analog a dual 555 timer with the right resistors and caps. will do the trick.

I don't want anything, the OP wants "Random" switching of many LEDs, not all at the same time. I personally cannot tell you how to attach a 555 to either switch many LEDs all at different times, nor how to make it random either.......

Perhaps you would be so kind as to show us all here and now. Thanks in advance. I am always very interested in leaning some new tricks.....

Here is the request of the OP:-

Tis the season! Yay.

OK. I need help. I want to design a small circuit that has 6 x 25mA white LED's. What I want the LED's to do is randomly go from bright to dim (about half intensity - never off). I don't know what other info would be required. Maybe - run off 12V car battery, no micro controllers. I was thinking of a sine generator running 10-15Hz split to say 4 paths. One path could be inverted. The other paths to have a lagging circuit. Would this work? What do I need to generate a slow sine wave? Also, how to design a lagging circuit? Any help or further questions welcome.

Thanks for the valuable input, the OP will be most happy.

Just an idea about 555s (or any other square-wave-producing devices) - if two square waves of slightly different frequencies (say 100Hz and 100.125Hz) were ANDed and used to drive the LEDs, it could give the desired effect (for one LED - inverted output would obviously give 2 LEDs in antiphase). If this is anywhere near practical, 3 dual 555s and a handful of Rs, Cs and FETs could do the biz.

Have a nasty feeling that the oscillators'd lock onto each other, tho', if the circuits were basically analog, and in close proximity.

_{(Still think a micro of some sort is easier - so don't shout about PICs in response).}

LOL!!

Why can't I "PIC" on you????? HUH????

Good info there..thanks...yes it can be random or a sequence that is not obvious. I want to create small clusters of LED's to have a twinkle effect. I want it to be in the background not something that draws attention with harsh bright to half intensity and back again.

More info I thought about... 'switching' bright to low intensity and rising to bright again with an obvious rise-fall time is what i want. Infinite (until it's switched off) operation. I see that a lot of Christmas lights may have this function all in a small box. I opened one but the IC is a blob of black goo.

Underneath that goo is a PIC.

I think you can fade these a little with large value Caps. Good luck.

Current-steering is one approach. One way might be to drive a multiplexer with a latched counter. Latch the outputs of a high-speed counter by means of a low rep-rate square-wave oscillator (a 555 being ideal). Use a second 555 (or 1/2 of a 556) to clock the counter at high speed, say, 10-100 kHz or so. As the two 555s are running independently, you effectively have a repeating 'dice-roller' that rolls at your low rep-rate. Connect each LED anode to the positive supply rail and each cathode to ground through a suitable current-limiting resistor. Also connect each line of the mux to each cathode, one line per LED, through a resistor and a diode (1N914 or equiv.) with the diode's cathode tied to the LED cathode and the anode to the mux resistor. When the mux line is low, the LED is unaffected. When high, the line biases the LED's cathode at a higher voltage, reducing the current through the device and dimming it thereby. You didn't say if you wanted to dim one LED at a time, btw. If more than one, use the latched outputs of the counter directly. Either way you go, be sure the device you use can source or sink sufficient current. Also, since white LEDs are really blue LEDs at heart, 5-volt TTL levels aren't gonna cut it directly unless your device has open-collector outputs. Or use CMOS if you can find it or use an octal line driver/level shifter or use discrete transistors and DIY one. Voila! Coding With Solder! :-))