24 LED Chaser Using PIC16F628A

[colin55]

I am not going to waste my time answering any more details on this merry-go-round.

 

[Mike - K8LH]

Hi Chip,

I apologize. Maybe this post is partly responsible for the misunderstanding?

Gents thank you for your comments.
You all have a valid point in your own way.
One thing you all overlooked that this is a chaser.
Think of a very compact 4017 counter with 24 outputs and it all makes sense.

This implies that you're only going to light one LED at a time. That's ok and I guess it's an interesting design but you don't really need 15 pins to do that.

If you have another application for this circuit in mind state your application and let's talk about it. i.e.: Light up all 24 LEDs at one time.

As it is the circuit does 3/24=1/8 with 25ma LEDs, no sink transistors.

Now you're talking about lighting 3 LEDs at a time, one in each group of eight, with a 1/8th duty cycle. No transistors required. That's a viable design. I like it. You might get about 2.5-ma "average" current per LED which is surprisingly bright.

Decrease the series resistors, and use lower mA LEDs (SMD) and you can light up all at the same time if you electrically supply it well.(LEDs of 5-7mA)

Now you're talking about lighting up to 12 LEDs at a time, up to four in each group of eight, at 50% duty cycle. No transistors required. You might get about 2.5-ma "average" current per LED which is surprisingly bright. You may perceive a difference in brightness depending on the number of LEDs lighted at one time in each group.

You should get the same "average" current per LED when lighting 3 of 24 LEDs @ 12.5% duty cycle as you do when lighting 12 of 24 LEDs @ 50% duty cycle.

Most LEDs (check your specs) can drive high current pulses for a short time. (I have 5mm LEDs that can pulse 120mA for a short duration-ms).

You lost me. I know about LED "pulse" or "peak" current specs'. Why are you mentioning it for this direct I/O design?

The rest of the brightness issues (so minor after above changes) can be made in software to compensate.

Your post seemed incoherent (to me). You said to consider the design as a pseudo 4017 with 24 outputs (1 LED at a time) then you talk about lighting all the LEDs. I guess I assumed this was a type of "learning exercise" better suited for a blog.

Mike (Pommie) is right. We should encourage you in this wonderful new adventure and so I hope you accept my sincere apology. Please let me know if I can help you in any way.

Cheerful regards, Mike

 

[Mike - K8LH]

Why are you (and Mike) saying this is not charlieplexed? It is clearly three 1x4 charlieplexed matrices.

Mike (Pommie), you are correct and I was wrong. This is clearly a Charlieplexed matrix.

If the design is a chaser like the "old" style Night Rider where only one LED is lighted at one time then we should probably show Chip' a 5-pin 20 LED design or a 6-pin 30 LED design.

If the design lights more then one LED at a time then I think it's a pretty good design in that it uses more I/O pins then necessary in order to improve duty cycle and brightness.

Kind regards, Mike, K8LH

 

[Chipwizard]

56 LED Light FX

Colin:
You have changed the intended design of the original post.
But since you want to create a new project then the way your are describing is not the best way to maximize the use of this PIC.

Use 8 ports of PORT-B for your drives and 7 ports of PORT-A for your sinks thru 7 transistors and multiplex 56 LEDs. Why limit yourself to 26 LED?
But again we are not talking about a simple chaser any more!
Regards,
Rom

 

[Pommie]

I am not going to waste my time answering any more details on this merry-go-round.

In that case you should have kept quiet from the start rather that criticize, very vocally, a fairly new poster. Please think first in future.

Mike.

 

[Chipwizard]

Hi Mike(k8):
Thank you for writing a post as I was a bit ticked off as how everyone just picked the original post apart without any attention to the original simple idea.
Based on what I read it seemed like everyone was trying to create a screen of 24 out of this chaser. That was not the idea.
Then I noticed Colin, Pommie and you were talking about 3 different ways of going about running 24 led at one time and accordingly I posted my response. Which created the confusion.
My apologigies to you as well sir. As I have come across your posts many times and I admire your clever thinking. As you have seen couple of mine as well. We can always agree to disagree.
Regards,
Rom

 

[Mike - K8LH]

Hi Rom (Chipwizard),

I noticed you have a new thread about mux'd LEDs and I was just curious about how the design in this thread worked out for you?

Regards, Mike