LED "running lights"

[scarygood536]

ok so I'm building a circuit using a 555 timer and a 4017 decade counter. I have 10 LED connected to the decade counter. What im trying to accomplish is having the first led in line turn on then off then the next one in sequence turns on and so on and so forth. When the last LED is reach the circuit will start from the beginning again non stop. timing is controlled by a 100k pot. What i have now is the circuit turns on and a random LED will turn on. I added a momentary push button to the circuit and if i keep pressing it it will keep randomly selecting LEDs to light, sometimes in rare instance it will light 3 at once. I would appreciate any help i can get in debugging or fixing my issue thanks.

attached is the PDF of the circuit I'm trying to build.

 

[Reloadron]

This is the second one today using a 555 and 4017. Less a push button to increment the 4017. If a push button is used to increment the 4017 it will produce random numbers due to switch bounce. You would need to debounce the push button switch.

Attached is an schematic of a 555 driving a 4017 decade counter divider with the 555 running in an astable mode. The frequency is between about .3 Hz and 3 Hz as drawn. It will produce an effect similar to the other attached image.

<EDIT> Drawing removed, I need to fix it! </EDIT>

<EDIT> Fixed drawing replaced </EDIT>

Ron

 

[scarygood536]

thanks for your reply... I do not want to have a switch in it though. The circuit should progress to the next LED automatically. Are you saying i need to add a de-bounce circuit even though im not planning on having a push button?

 

[Reloadron]

No, the circuit you want I just posted on an Edit of my post. Damn, I can't believe I screwed up that circuit.

You do not need debounce if you do not use a button. I believe the effect you want is in my first post along with the circuit. The LEDs sequentially advance and then recycle over and over again.

Ron

Ron

 

[scarygood536]

i took a look at your schematic. I did not find it to be much different than the circuit i was working with. However i found out if i remove the reset all to gether and remove the pot from the proto board i can push a button and it will light each led 1 at a time and start over just cant get it to do it by itself.

based on this experiment i would have to say the issue is the 555 not working

 

[Reloadron]

If you look close at the two circuits you will see some important differences. I am not sure why the 100K pot is where it is in series with R3? You are correct to assume your 555 is not oscillating. If you look at my circuit it is a common everyday 555 astable oscillator circuit. C1 charges through R1 & R2 and the discharge path is only through R2. That layout is pretty important. As drawn your circuit would not work.

Ron

 

[scarygood536]

Ahhh thank you so much i got it working to a point. having trouble changing speeds but ill have to play around with the resistance. thanks a lot for your help

*although adding a cap did the trick

 

[Reloadron]

Good deal. Where was the cap added? Anyway, glad it is showing signs of life.

Ron

 

[scarygood536]

a 100uF was added between pin 2 and ground. so your 4.7 cap was completely missing in my circuit lol. changing capacitance changes speed, also adding a pot where the 1m resistor is also changes speed although it isn't nearly as noticeable.

it seems when i work with the 555 timer i always run into oscillation issues. IO tried a similar circuit yesterday trying to do a knight rider circuit but i wasn't getting any results, all the lights came on and couldn't change outcome.

 

[audioguru]

The original problem was that when the circuit was powered then a random LED would light. Sometimes two LEDs might light.
It is because a "power up reset" circuit (a resistor and capacitor at reset pin 15) is missing.

I think some of the problems are fixed by adding a second power supply bypass capacitor as is recommended on the datasheet for the LM555. The 555 produces a huge supply current spike of 400mA each time the output switches which messes up the CD4017. An additional supply bypass capacitor (minimum 1uF) holds up the supply voltage during the current spike.

 

[audioguru]

a 100uF was added between pin 2 and ground. So your 4.7 cap was completely missing in my circuit lol.

Your circuit used a 10uF capacitor. The frequency would have been about 1 blink per second to about 200 blinks per second as shown on the datasheet. With 100uF then there will be one blink each 10 seconds to 20 blinks per second.

all the lights came on

They do when the oscillator frequency is too high.

 

[scarygood536]

interesting. Is that what was wrong with the knight rider circuit or the current circuit? Currently the running lights is working when adding a cap between - and pin 2

 

[audioguru]

interesting. Is that what was wrong with the knight rider circuit or the current circuit?

You said the Knight Rider circuit had all the lights on.

Currently the running lights is working when adding a cap between - and pin 2

Your schematic showed a 10uF capacitor between - and pin 2 which makes the oscillator run 10 times faster than a 100uf capacitor.
The calculation for it is in the datasheet and there is also a graph that shows the values and the resulting frequency.

 

[scarygood536]

ok i understand now. thanks for the insight. i think ill try the knight rider again adding in the caps you mentioned. thanks for your help
scary