LEDs, 555s, Flashers, and Light Chasers

mxabeles

Joined Apr 25, 2009
266
thanks for that wookie
ok, i ordered all the 68 ohm resistors because that was the amount of resistance i need for my high brightness led if they being subjected to 5v +.
Again, the wiring i have for the 555 timer does work :
pin 1 : ground
pin 2 : timing capacitor to ground, also tied to pin 6
pin 3 : output
pin 4 : tied to pin 8 (vcc)
pin 5 : voltage input, but brought to ground with cap if unused
pin 6 : Resistor 2 to pin 7
pin 7 : resistor 1 to pin 8
pin 8 : vcc

thats what I have been using for over a year and it never failed me!
Interested to hear from your perspective what is gone wrong in this configuration.
Again, thanks for all the info.
Best,
M
 

Thread Starter

Wendy

Joined Mar 24, 2008
23,408
OK, the planned updates are finished on the main article (finally). After a while for proofing it I'll transfer the changes to the blog. I also have to update the index page.

This may be the final version, unless something else comes up that I think needs adding.
 

spelcaztr

Joined Feb 16, 2011
12
hello sir. Nice tutorial sir bill. I would like to ask if it is possible to light 24-32 LEDs with 4022/4017 IC in one sequence?? Well i don't think that it is possible except by adding a transistor but i don't have any idea where and what specific to use?? I don't have any specific voltage source yet so i think it could be possible.

Or maybe i would just use 8 4017/4022 IC to drive three LEDs each??
 

Thread Starter

Wendy

Joined Mar 24, 2008
23,408
Do you want a 32 step sequencer, or mulitiple LEDs lite per sequence?

A 32 step sequencer would take qty 4 4017s. Very doable.
 

Thread Starter

Wendy

Joined Mar 24, 2008
23,408
I have updated the following chapters,

Chapter 5, redrew Figure 4.3 to make it more complete, with minor revision to the paragraph below. AudioGuru stongly suggested this over a year (or two?) ago.

Chapter 10, added Figure 10.3, and rewrote much of the MOSFET section.

Chapter 12, revised schematic on Figure 12.2 Example D to correct problems with MOSFET circuitry. Also revised Figure 12.4 for the same reason.

Added an appendix, to allow links to printed circuit board designs that people have done for various designs. Many of the printed circuit layouts are not exact duplicates of the circuitry, but close enough. Many of the changes are actually improvements in the original designs.
 

BSB

Joined May 31, 2011
1
Hi.

In Fig 4.2 (Chapter 5) the components types designations for CR1,2 ?
I understand from the symbol they are just regular diodes
What is the function ?
 

Thread Starter

Wendy

Joined Mar 24, 2008
23,408
The first number in any figure number is the chapter. You have managed to find a typo, for which I thank you. It will be fixed.

This is the drawing you are referring too.



The diodes in question are steering diodes. The charge the capacitor through one side of the pot, then discharge through the other side of the pot. The end effect is the frequency is relatively stable, but the duty cycle is varied according to the pot settings.

I've explored this circuit a bit more in this article...

555 PWM Oscillator
 
I found your site very recently and saw the comment about "Knight Rider style sweeping light" preceding circuit 12.3. Circuit 11.4 can be modified to give the save effect and display 13 LEDs.
 

rrmestl

Joined Dec 27, 2019
2
Hello, I'm new to the site, and found the link to https://forum.allaboutcircuits.com/threads/100-led-chaser.81140/ (100 LED chaser), and wondering if any updates/improvements have been made to it...
Actually not looking for that many lights, just a few more than the normal 10 LED decade counter sequence that the simple kits achieve. Trying to setup a chasing light for a model (Pegasus Alpha-Centauri UFOs), it needs 14 LEDs, blinking one-at-a-time, and would like to make it myself.
Thank you in advance!!!
 

Audioguru again

Joined Oct 21, 2019
6,647
Datasheets for the CD4017 show how to cascade them for more outputs by using an AND gate. A simple AND gate can be made with two diodes and one resistor. Change the output from the second CD4017 for fewer outputs.
See here:
 

Attachments

rrmestl

Joined Dec 27, 2019
2
Datasheets for the CD4017 show how to cascade them for more outputs by using an AND gate. A simple AND gate can be made with two diodes and one resistor. Change the output from the second CD4017 for fewer outputs.
See here:
Thanks Much Audioguru!!!
If I would have known better to search for "cascaded CD4017" I could have found at least one article that you had already previously posted the answer for this same question... (facepalm) ;)
Will play with it and see how it goes...
Thanks again!!!
 

soyez

Joined Aug 17, 2020
51
LEDs, 555s, Flashers, and Light Chasers

One of the most common requests at All About Circuits is various methods of flashing LEDs. I'll try to show most of the techniques used for this purpose that have been covered on this site, explaining how and why along the way.


Index......................................................Skill Level

1....LEDs.....................................................................Beginner
2....Current Limiting.......................................o...Beginner/Intermediate
3....The LED / Resistor Only Bargraph....... ..Beginner/Intermediate
4....The 555 Integrated Circuit.........................Beginner/ Intermediate
5....The 555 and PWM.........................................Intermediate
6....Low Power Applications.............................Intermediate
7....The Joule Thief................................................Intermediate
8....From Four, Twenty.........................................Intermediate
9....Light Chasers.............................................o....Intermediate
10..Transistor Drivers..........................................Beginner/ Intermediate
.......BJTs
.......MOSFETs
11..Making Patterns........................................,/..Intermediate
12..Special LED Effects...................................,...Beginner/Intermediate
.......Throbbing LEDs
.......Fading LEDs (AKA Comet Trails)
.......Flickering LEDs (Fire!)
.......RGB LEDs (Millions of Colors)
....Conclusion
....Appendix

<Continued in next post>
much obliged you have posted a detail account upon it
 

DK3250

Joined Jul 15, 2020
13
I'm a beginner in electronics; I'll read this thread many times to extract all the nice info.
As a beginner, however, I often want to go back to basic principles - in this case to a circuit without IC, only transistors, resistances and capacitors.
On another site, I saw this diagram which I found useful:
1597939981438.png
Maybe some other beginners will find it beneficial too.

By the way, your pun line: "Good enough is enemy of the best." is wrong - it should be the other way around: the best is the enemy of the good - according to Wikipedia this is attributed to Voltaire.
 

Thread Starter

Wendy

Joined Mar 24, 2008
23,408
I like the quote as it is. I got it from an engineer at work when I was a grunt technician. Nice circuit.
 

stspringer

Joined Oct 1, 2019
81
Chapter 4: The 555 Integrated Circuit

This IC has been around for a long time, over 30 years. The 555 IC could have been designed for LEDs, it is as if they were made for each other. I've written several articles about it, and won't go to the depth I did about the LEDs. Some internals of the 555 IC do need covered, since they relate to LED voltages.

The 555 has a digital output. It is either switched to the positive voltage (high) or the negative (low). An equivalent drawing of it's output would look something like this:


.........................................................Figure 4.1

Although Circuit #1 and Circuit #2 look different, they are pretty similar in performance. Generally I prefer circuit #2, but #1 will handle some special LEDs that are a red and green LED in the same package. Alternate between the LEDs fast enough, and it appears yellow. In both cases the 555 output shorts one side or the other, leaving the opposite side to light up with full power. The two internal diodes shown (which are actually two base emitter junctions) generate 1.2V, which swamps the LED Vf it is parallel to.

So far I have been showing how to light the LEDs at full power, and how to select the resistor for this. An LED will light up with 1ma and be visible, which will work for a lot of indicator applications. Many cases, such as my experiments, I use a 1KΩ for convenience, and don't worry about it. In the above application this would work out to 6.5ma, which works well enough.

Another issue to be aware of is what the 555 can provide in current. I've already shown it's voltage limitations, but the transistors inside the IC can only provide 200ma before being damaged. There is a general rule in electronics that you should only use half what a component can provide, to make sure the part lasts its expected life. I don't always follow this rule myself, but you need to be aware. The 555 is also rated for 4.5 VDC to 18 VDC, generally this will set the power supply limits of the circuit.

The 555 is a very open ended ICs, and have a lot more uses than just flashers, but for the purposes of this article we'll concentrate on the flasher applications. Shown in Figure 4.2 are two basic configurations that can be used to flash LEDs.


........................................................ ............ .........................Figure 4.2

Oscillator #1 is in the family of Hysteretic Oscillators, which is usually made with op amps. The 555 version adds some its own twists, since the output isn't quite rail to rail (as shown by the two diodes in the first illustration). Its duty cycle is hard to predict, as it is somewhat dependent on power supply voltage. The higher it's power supply voltage, the closer to 50% it becomes. However, for many applications the duty cycle imperfection is hard to see, so it can be used in a large number of applications with good results. You can even put a potentiometer for R1, which allows the flasher to cover a really large range of rates and frequencies.

Oscillator #2 is straight out of the 555 datasheet. With the addition of a second resistor it overcomes all the problems with oscillator #1, including the 50% duty cycle. For 50% R1 needs to be as low as possible, which is balanced by the fact that at one point R1 is completely across the power supply, thus being one of the components that set the total current draw of the circuit.

C2 is a bypass capacitor. For a single 555 on a battery you don't really need C2 or any other bypass capacitors, which is why I show it as a "ghost" image. There is an exception to this rule, which will be covered in the following article.

So what if you need a single LED that is one only 10% of the time? It is simple, use the D1 side for your LED. If you need 90% then use the D2 side for your LED.

<Continued in next post>
Are you talking about circuits for high amp LED's like say 2 or 3 amps
 
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