I have played around with a circuit that flashes 8-10 led's randomly at a second or 2 on and 10-15 seconds off using 555's. What I'm wondering is... is there another single chip that could be used to do about the same thing that the 8-10 555's are doing and make it simpler. Would there be a simple micro processor that would do the same thing that could be programable? Any info you could provide would be greatly appreciated since I'm not real good at designing circuits. I'm pretty much just beginning.

Thanks,

Mike

 

well it is not random....
all the leds have a fixed frequency with wich they flash, but the frequencies are different so it gives you the impression that they flash random
one "simple" thing it to connect them to a computer and use a software to control them, but you say that you are a beginner.
i dont know you can use a smaller number of ics.
you couls use an EPROM and program it so that the sequence seems random.
i think that the 555 version is the simplest, but you have to build the circuit 8-10 times, each one for a led.
the 556 has 2 555 timers inside so you can reduce the number of ic's to half.
i will think of something else.

 

I'm afraid that if you want a design that is simpler than yours, you will probably have to show us yours.

 

thats true.
but from what i understand you just have 10 leds connected to 10 555 oscilators, and thetre frequency is different so you have the impresion that the 10 leds flesh randomly.

 

hey i think i have an idea....
use a 555 to generate pulses of a highter frequency and another 555 to generate a smaller frequncy. use a counter wich gets the signal from the first onew only when the ouput of the second 555 is high and for each outhput of the counter connect a FF and drive the led with it. this way you will have a little bit smaller number of ICs
but i dont think it will work.....

 

Thanks all for your help. I thought it was about the simplest circuit. Mainly I am trying to use fewer components. I'm not sure, but it looks like the 558 will help out a lot. I'm just not sure yet if each section can be set so the led will be on for a second and off for about 8 seconds and then the other 3 sections off just a little bit from there so it will look random. Then it would just take 3 chips etc.

 

Cycling (on-off) times of the 555 are adjustable. Normally, we attempt to use a 50% duty cycle which approaches a true square wave. In this configuration the pulse 'on' time is the same as the 'off' time. However, if you are using a standard R-C (resistive-capacitive) circuit to set the timing pulses, you can change their values to a wide array of duty cycles. For the formulas, do a web search for 555 calculators - there are quite a few available that will do the math for you.

 

but how do you build a 555 with a 50% duty cicle?
i think it is a bit more complicated. probalby some diodes are needed

 

Hi crunch.

Instead of using 8-10 555's (or 5 556's), you can build a circuit with just one IC by using a microcontroller. If you use for eg. PIC16F84 you can connect up to 13 LEDs and create a truly random flashing sequence.

 

true indeed......

 

For the calculation:

http://webhome.idirect.com/~jadams/e...s/555calcs.htm

One that I used was 0.000001 F, R1=1,000 ohms, R2=26,320 ohms = 2.685 pulses/sec @ 50.9 duty cycle. I'm not sure you can get a 'perfect' square wave.

 

well, with the normal oscilator you cannot get a square wawe beacause the charging is done trough one resistor and the discharging is done trough that resistor and another one. so you can do, as i see from your values put a resistor with a value much bigger than the other one and you will get a nearly square wave. but i think that for 50.9% you cannt notice that without mesuring, because the frequency is qite high.(>1Hz)

 

Not at all complicated, only a single diode in between pin 7 and pin 6 in astable configuration.

__________________
"There is no way to peace, peace is the way!"

 

well i think i know how. but a little schematic from you will do.
p.s. you promised me that high gain audio amp....

 

Ya, sure why not. i haven't forgotten that. But, please wait, I got to search my old little circuit book, in which I used to draw my schematics in school days when I didn't had a computer.

__________________
"There is no way to peace, peace is the way!"