Unsynchronised Blinking LED Array

[Diversified Multi-Robert]

Hi. This is my first time posting at electro-tech-online. I have a fairly simple question for the more advanced electronics afficianados. Here's my question. I have a schematic for a blinking led that runs on a 555 timer chip. The schematic checks out. However I went to lay out five of them in a parallel array and things got screwy. Basically two or more LED's would go off or on at the same time much more often than one would expect to be chance. It's a very slow blink rate so its easy to notice when they swich. I want them to operate as individual lights. The blink rate for each LED is uniform and periodic and is slightly different from the blink rate of the others.

So basically .. how could I better wire a multiple LED array for unsynchronised blinking lights?

Also.. is there software out there where I can test the response of the LED's in a simulated environment?

Any help would be super.
Robert

 

[ericgibbs]

hi,
If the 555's are the older TTL type, they can 'inject' noise into the power supply rail, when their output pin #3 change state.

You should always have decoupling capacitors, say a 100nF near the 555 across pin#8 and pin#1 of each 555. also say a 47uF or higher across the supply rails.

 

[Diversified Multi-Robert]

Thanks for the help. I however have one quick question. What are the supply rails? Is that pin #8 and pin #2? I'm kinda new at this.

 

[ericgibbs]

Thanks for the help. I however have one quick question. What are the supply rails? Is that pin #8 and pin #2? I'm kinda new at this.

hi,
They are the +V supply and 0V supply wires. For a battery supply thats, +V terminal and the -V terminal [ the -V terminal is considered to be 0V reference]

Those are the 555 IC pin numbers. pin #1 is 0V and pin#8 is +V

 

[Diversified Multi-Robert]

Hello. I just noticed something. In my email auto notify the message says..

(1st)
"You should always have decoupling capacitors, say a 100nF near pin#8 and pin#4 of each 555. also say a 47uF or higher across the supply rails."

But in the forum it says..

(2nd)
"You should always have decoupling capacitors, say a 100nF near the 555 across pin#8 and pin#1 of each 555. also say a 47uF or higher across the supply rails."

So I drew two drawings under the first instruction from email. One of them has the 47uf cap inside the individual led circuit and the other drawing it's outside. Im not sure which one is the way to do it since both have 47uf caps connected to 0V and +V.

Thanks for your help.

 

[ronv]

Pin 4 is normally tied to pin 8.
Then a .1 ufd. from pin 1 to 8 and a 47ufd. also from pin 1 to 8.
It is also good practice to add a .01ufd from pin 5 to ground. (pin1)

 

[Diversified Multi-Robert]

Oh ok makes sense..

 

[ronv]

Pin 4 is minus reset. It (pin 4) is tied directly to pin 8 (positive supply).

 

[Diversified Multi-Robert]

Here's what I have. (Attachment) I'm new to electrical forums where people ask for advice. So this is a big relief for me that I was able to find others who are willing to help who are knowlegable. I'll add a star to your reputation(s).

 

[ericgibbs]

hi,
Your circuit looks OK,

I had a problem posting, I noticed that I had pin#4 instead of pin#1, I edited the post, but the posts disappeared and I got into a 'post' loop. I hope the multiple posts didn't cause you too many problems.

I have reported the problem to Admin.

 

[Mr RB]

Just as an alternative suggestion, you can make a LED flasher from a schmidt inverter gate as in a common 7414 IC.

The 7414 has 6 gates so you can make 6 LED flashers. This is cheaper and simpler as each LED flasher only needs 2 parts, a resistor and a cap.

So total parts for 6 LED flashers is;
7414 IC (74ACT14 is fine)
6 resistors
6 caps
6 LEDs (and 6 LED current-limiting resistors)

 

[ericgibbs]

hi Roman,
The circuit is already built using 555's, the problem the OP has is/was most likely to having no decoupling on his supply from a battery.

 

[Mr RB]

Yeah I saw that... It's just that I hate the idea of five ICs and all the associated parts when it can be done with one IC and a handful of parts.

I guess he did ask; "how could I better wire a multiple LED array for unsynchronised blinking lights?"

 

[Diversified Multi-Robert]

Oh hey! Thanks for the input Mr RB. I had been away from the project for quite some time and had not scrolled down in my emails to see there where reposts on the topic.

I had tried the circuit as described but I was not able to un-couple the LED array even with different orientations of the caps. I'm not sure what to do. This was the first circuit I designed and perhaps I could make it work with the 7414 IC.

 

[Diversified Multi-Robert]

Actually second thought. It appears that the 7414 would not give that unsyncronised effect that a series of multiple 555 timers would give. Is this a fair assumption? I would be interested in any ideas even if it meant I would have to revamp and rebuild the circuit. Thanks.

 

[Mr RB]

The 7414 will give you 6 fully independant oscillators. Each oscillator just needs 1 resistor and 1 cap.

You will still need a good power supply, preferably a 5v regulator like a 7805 and decent size caps on the regulator.

 

[mdorian]

Why don't you use a pic16lf628 with a pseudorandom algorithm , can drive up to 16 LED without other external components except the limiting resistors for LED-s. I'm sure somebody will help you with a simple program for it

 

[audioguru]

You have four 0.1uF capacitors but only one is needed.
You have two 47uF capacitors but only one is needed.

 

[Diversified Multi-Robert]

Im thinking I'm going to try to stick to the original suggestion by ericgibbs.

Mr RB: Thanks for the input I'll keep it in mind. I may decide to switch over.

M Dorian: That's another good idea I'll also keep that in mind however I dont think I'm at that skill level just yet.

Audioguru: I'm posting the current up to date drawing. Within it are 5 caps of each type. There are 5 LEDs in parrallel listed under "(A)". You mentioned that only one 47uf and one 0.1uf is nessisary. Im not sure where they go. I would guess: around the battery. However I'm not sure.

Many Thanks.

 

[ericgibbs]

hi,
Fit one 47uF and one 100nF capacitor across the +V and 0V of the supply, try the operation of the project.

If you experience problems due to 'noise' causing interactions between the 555's, fit a 100nF across pins 8 and pin 1 of each 555.