Require help with LEDs and some PCB design

Thread Starter

William A Rose

Joined Feb 5, 2022
45
Hi folks. I just joined. Got an auto-message from an Admin called jrap. I replied. One day I'll figure out how this site works. I am the novice of novices. I know a whole lot of little stuff. Enough to probably toast any component I touch. Ah well. My ambitions are not broad. I just want to mess around with LEDs and do some PCB design (if I can ever learn one of the three programs I found), some designing of LED circuits and some soldering. Fun stuff. Keeps an old man busy barring any heart aggravation. That is a long story. Hey, I'm still alive. God sustains me. He has to be. I'd have checked out 15 years ago if He were not looking out for me. Eight heart attacks (arguably) and still ticking. :)

Thanks for having me and probably for putting up with me in the future. There is so much I don't know about this stuff. It seems to be an expensive hobby. I have only toasted one red 5mm LED and one Trimpot. The little blue ones made by Bourn. 3362P is the number molded into it.

Y'all take care.
 

Ya’akov

Joined Jan 27, 2019
5,657
Welcome to AAC. There are a lot of folks around here that really like to help neophytes, so you will get plenty of help.

Asking questions is great, just make sure you provide enough information when you do to get off to a good start. If I had one piece of advice on that*, it would be: if you run into a problem trying to solve a problem, and need help, be sure to start by describing the first problem you were trying to solve. Don’t mistake your trouble with the solution for the problem itself.

You’ll get a lot better help if people know what you set out to do before you tell them what about your attempt isn’t working for you.

I hope you become a regular, and remember, if you know just one thing more than a person who needs help you can help them, don’t hesitate to help out when you know answers.

*As it turns out, I have much more than one piece of advice, but one step at a time is a good policy.

[EDIT: noticed a typo, fixed it, and couldn’t resist adding puncitation and a footnote for clarity.]
 
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djsfantasi

Joined Apr 11, 2010
8,323
At the beginning of every forum, there is a post titled (something like) “Please read before posting in the xxx xxxx xxxx forum”. This thread outlines how to construct your post in the manner likely to get the best help possible.

At the bottom of every page, there is a link to the forum’s “Terms and rules”. You should periodically review these.

There is also a “Help” link which you should find useful.

Enjoy your time here. I’ve lost track of the number of years I’ve been a member.
 

atferrari

Joined Jan 6, 2004
4,593
At the beginning of every forum, there is a post titled (something like) “Please read before posting in the xxx xxxx xxxx forum”. This thread outlines how to construct your post in the manner likely to get the best help possible.

At the bottom of every page, there is a link to the forum’s “Terms and rules”. You should periodically review these.

There is also a “Help” link which you should find useful.

Enjoy your time here. I’ve lost track of the number of years I’ve been a member.
Almost 12 dj and counting.
 

dl324

Joined Mar 30, 2015
14,458
Welcome to AAC!
Thanks for having me and probably for putting up with me in the future. There is so much I don't know about this stuff. It seems to be an expensive hobby.
Most members are quite accommodating as long as you're opened to actually learning vs. guessing and only wanting to do things your way.

What equipment do you have? What kinds of circuits do you think you'll be interested in?

Keep in mind that schematics are the best way to describe circuits. If you haven't seen enough well drawn schematics to draw some of your own, don't worry, someone will critique any that are poorly drawn in the hopes of getting you headed down the right path.
 

Thread Starter

William A Rose

Joined Feb 5, 2022
45
Hey folks, what do you think of this timer layout? The added diodes are interesting for their function. I suppose an LED might work, too? I do have other questions. For example, why is a particular electrolytic capacitor value chosen? I understand why the voltage rating is selected, but not the Farad value. What is the difference between 10 or 22 or 47 or 470 microfarads? The higher the capacitance, the more it can zap you, but how do we determine a sufficient value? I know this will sound like a dumb question to you all, probably. To me, it is not. I just want to understand.

What about the ceramic capacitor - 104? Why that specific value, etc.?

I have seen many astable timer schematics that show all sorts of different resistor values. I understand why different values are needed for different LEDs, but in the timer circuit, why isn't there a standard?

1644159702059.png

Also, I found this for doing calculations and it is really handy!

1644160062626.png

Thanks, folks.
 

Ya’akov

Joined Jan 27, 2019
5,657
There is an important property of resistor-capacitor circuits called the RC Time Constant notated by the Greek letter τ (tau). A capacitor discharging through a resistor will take a certain period of time based on the values of the two components.

It is calculated such that for charging it is from 0V to about 63.2% of the voltage used to charge is, or for discharging, it is down to about 36.8% of the initial voltage. This means it takes more than 1τ to fully charge or discharge.

You can find quite a few RC time constant calculators on the web, like this one. You can use it to design a 555 circuit with a particular on or off time, and to do other things that have to do with much higher oscillating frequencies.
 

Thread Starter

William A Rose

Joined Feb 5, 2022
45
Oh yeah, Because of limited space on the designs, I am having an interesting time selecting components. I need a power source. A battery, of course. Lots of mAh and as small a footprint as possible. There's only so much room on the snowflakes. Looks like the smallest I can make is probably going to be an 8-Inch (203.2mm) and be able to have it do what I want. The smaller designs are probably not going to be all blinky and cool. Just a constantly-on setup. I don't know. I did make a Christmas Tree from a kit that is pretty cool. It uses 3 AA batteries in a holder that serves as the tree stand too. I'll find a pic and post it. It doesn't do what I am wanting the snowflakes to do. I guess I am thinking of going with a 6 volt supply. That is enough to power the ICs and the LEDs, I hope. More voltage would be better, and for sure more mAh, but I can only do what I can do.

Here is a pic of my first attempt at designing an 11-Inch snowflake. I don't like the way it turned out. I am redesigning it in an 8-Inch format. It is not finished, yet.

11-Inch LED Snowflake - Design One - JPG.jpg

Here is the progress of the 8-Inch redesign....I am nowhere near finished yet.

Reworking of 8-Inch Snowflake - Design One - JPG.jpg
 

dl324

Joined Mar 30, 2015
14,458
what do you think of this timer layout?
I don't know if that video ever showed a proper schematic, but I'd stay away from any content that draws schematics like the one you referenced. It's very difficult to discern circuit function, whereas it can be discerned with a glance with a conventional schematic. I'll redraw more conventionally later.

EDIT: better schematic. I think I got pot rotation correct but looking at that "schematic" was tedious.
1644168236895.png
EDIT 3: Made a wiring mistake. THR and TR should be connected to C2. Corrected in post #45 and here.
1644336835465.png
With a properly drawn schematic you can easily see that on time is determined by the path through D2 and off time is determined by the path through D1. Pin 5 should be bypassed to ground so no noise can couple to that comparator input and affect timing.

The way the YouTube schematic was drawn was awful. No component designators and with colored wires, the author didn't need to use wire breaks at crossings. We never draw wires over components or text. When you see stuff like that, you should think "amateur" and avoid their "work".

When you draw symbols, the strong preference is for inputs to be on the left and outputs to be on the right. This supports schematics drawn with "flow" primarily left-to-right and top-to-bottom. Wiring type diagrams can never conform to this standard.
I understand why different values are needed for different LEDs, but in the timer circuit, why isn't there a standard?
There are specific circuit configurations for astable and one shot applications, but the resistor and capacitor values are varied to determine frequency, duty cycle, and pulse width.

EDIT 2:
Here is the progress of the 8-Inch redesign....I am nowhere near finished yet.
It looks like you're planning to have CD4xxx IC's drive multiple LEDs in parallel with no current limiting resistors. That's not a good design practice because LEDs aren't matched by forward voltage by default (brightness binning is more common). The amount of current that CD4xxx outputs can sink or source depends on supply voltage and it isn't as much as you'd like.

For battery operated applications, putting LEDs in parallel without ballast resistors is okay if the battery can't provide enough current to destroy them. They do it all the time in those cheap LED flashlights, but you could end up with some that end up with some dead LEDs.
 
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Thread Starter

William A Rose

Joined Feb 5, 2022
45
I don't know if that video ever showed a proper schematic, but I'd stay away from any content that draws schematics like the one you referenced. It's very difficult to discern circuit function, whereas it can be discerned with a glance with a conventional schematic. I'll redraw more conventionally later.

EDIT: better schematic. I think I got pot rotation correct but looking at that "schematic" was tedious.
View attachment 259869
With a properly drawn schematic you can easily see that on time is determined by the path through D2 and off time is determined by the path through D1. Pin 5 should be bypassed to ground so no noise can couple to that comparator input and affect timing.

The way the YouTube schematic was drawn was awful. No component designators and with colored wires, the author didn't need to use wire breaks at crossings. We never draw wires over components or text. When you see stuff like that, you should think "amateur" and avoid their "work".

When you draw symbols, the strong preference is for inputs to be on the left and outputs to be on the right. This supports schematics drawn with "flow" primarily left-to-right and top-to-bottom. Wiring type diagrams can never conform to this standard.
There are specific circuit configurations for astable and one shot applications, but the resistor and capacitor values are varied to determine frequency, duty cycle, and pulse width.

I will be building the circuits on a breadboard long before I build an actual prototype.

EDIT 2:
It looks like you're planning to have CD4xxx IC's drive multiple LEDs in parallel with no current limiting resistors. That's not a good design practice because LEDs aren't matched by forward voltage by default (brightness binning is more common). The amount of current that CD4xxx outputs can sink or source depends on supply voltage and it isn't as much as you'd like.

For battery operated applications, putting LEDs in parallel without ballast resistors is okay if the battery can't provide enough current to destroy them. They do it all the time in those cheap LED flashlights, but you could end up with some that end up with some dead LEDs.
Dennis,

Thanks for the reply. I did state I am nowhere near finished with that drawing. Even the 11-Inch is wrong. Keep in mind I am a novice - I don't know what I am doing, necessarily. You did mention a few things that I find very useful, particularly about schematic drawing standards. I picked up on that right away. My designing is far from complete. This whole thing is a work in progress.

I plan to create a proper schematic once I get it all figured out. There is math to be done that I haven't gotten to just yet. There are many things I haven't gotten to yet.
 

dl324

Joined Mar 30, 2015
14,458
Keep in mind I am a novice - I don't know what I am doing, necessarily.
That's why I mentioned having parallel LEDs and the current sink/source capability of CD4xxx. You see all sorts of LED flashlights with LEDs in parallel without ballast resistors. They don't care if LEDs start burning out, and they don't care if you don't buy from them a second time. When you're making millions of widgets, saving a few cents on each adds up. For one off designs, there's not much point in pinching pennies.

Here's the relevant part of the CD4017 datasheet. This is Harris/RCA/TI, but the specifications for all manufacturers should be about the same because that's the whole point of having multiple sources. If a part is significantly different, it should have a different part number.
1644175522120.png
1644175549220.png
If you operate at 15V, the device is only guaranteed to provide 3.4mA at room temperature. You can draw more if you're willing to let the output voltages be outside of the specifications for logic LOW or HIGH.

74AC can sink and source more current, but they operate over a smaller voltage range (1.5-5.5V).
 
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Thread Starter

William A Rose

Joined Feb 5, 2022
45
There is an important property of resistor-capacitor circuits called the RC Time Constant notated by the Greek letter τ (tau). A capacitor discharging through a resistor will take a certain period of time based on the values of the two components.

It is calculated such that for charging it is from 0V to about 63.2% of the voltage used to charge is, or for discharging, it is down to about 36.8% of the initial voltage. This means it takes more than 1τ to fully charge or discharge.

You can find quite a few RC time constant calculators on the web, like this one. You can use it to design a 555 circuit with a particular on or off time, and to do other things that have to do with much higher oscillating frequencies.
Fascinating, but well above my pay grade.
 

Thread Starter

William A Rose

Joined Feb 5, 2022
45
I don't know if that video ever showed a proper schematic, but I'd stay away from any content that draws schematics like the one you referenced. It's very difficult to discern circuit function, whereas it can be discerned with a glance with a conventional schematic. I'll redraw more conventionally later.

EDIT: better schematic. I think I got pot rotation correct but looking at that "schematic" was tedious.
View attachment 259869
With a properly drawn schematic you can easily see that on time is determined by the path through D2 and off time is determined by the path through D1. Pin 5 should be bypassed to ground so no noise can couple to that comparator input and affect timing.

The way the YouTube schematic was drawn was awful. No component designators and with colored wires, the author didn't need to use wire breaks at crossings. We never draw wires over components or text. When you see stuff like that, you should think "amateur" and avoid their "work".

When you draw symbols, the strong preference is for inputs to be on the left and outputs to be on the right. This supports schematics drawn with "flow" primarily left-to-right and top-to-bottom. Wiring type diagrams can never conform to this standard.
There are specific circuit configurations for astable and one shot applications, but the resistor and capacitor values are varied to determine frequency, duty cycle, and pulse width.

EDIT 2:
It looks like you're planning to have CD4xxx IC's drive multiple LEDs in parallel with no current limiting resistors. That's not a good design practice because LEDs aren't matched by forward voltage by default (brightness binning is more common). The amount of current that CD4xxx outputs can sink or source depends on supply voltage and it isn't as much as you'd like.

For battery operated applications, putting LEDs in parallel without ballast resistors is okay if the battery can't provide enough current to destroy them. They do it all the time in those cheap LED flashlights, but you could end up with some that end up with some dead LEDs.
I found another proper schematic similar to the one you supplied. It has a bit more information in that it shows, for example, the pin connections for the Trimpot. I found the other image you didn't like quite valuable. It is nice to the actual components laid out alongside a proper schematic. It helps me immensely.

Here is the similar schematic that I found (screen capture from a video). Perhaps you will approve of it.

1644221855785.png
 

Thread Starter

William A Rose

Joined Feb 5, 2022
45
This is my flag layout. My goal is to have all of these LEDs constantly on at maybe 80% brightness and "randomly" pulse the LEDs in each section at 100% brightness. The stars will be pulsed the way you would draw a 5-point star and then the center LED is pulsed last. Each star will be pulsed "randomly". In each stripe and in the blue LEDs in the Union, they'll just be on and pulsed "randomly". I believe I can achieve this effect by wiring them to the outputs of the 4017s according to the random number sequence I have generated with a generator I found on the internet. This will require a great many components. I don't know a better way. I do not wish to fool with a microcontroller. That is above my pay grade. I just want to have a bunch of chips, wires, and solder. Oh my.

1644222636199.png
 

Thread Starter

William A Rose

Joined Feb 5, 2022
45
Welcome to AAC. There are a lot of folks around here that really like to help neophytes, so you will get plenty of help.

Asking questions is great, just make sure you provide enough information when you do to get off to a good start. If I had one piece of advice on that*, it would be: if you run into a problem trying to solve a problem, and need help, be sure to start by describing the first problem you were trying to solve. Don’t mistake your trouble with the solution for the problem itself.

You’ll get a lot better help if people know what you set out to do before you tell them what about your attempt isn’t working for you.

I hope you become a regular, and remember, if you know just one thing more than a person who needs help you can help them, don’t hesitate to help out when you know answers.

*As it turns out, I have much more than one piece of advice, but one step at a time is a good policy.

[EDIT: noticed a typo, fixed it, and couldn’t resist adding puncitation and a footnote for clarity.]
Hehe. "Puncitation". I love that. I'm gonna use it, too!!!!!!!!
 

Ya’akov

Joined Jan 27, 2019
5,657
This is my flag layout. My goal is to have all of these LEDs constantly on at maybe 80% brightness and "randomly" pulse the LEDs in each section at 100% brightness. The stars will be pulsed the way you would draw a 5-point star and then the center LED is pulsed last. Each star will be pulsed "randomly". In each stripe and in the blue LEDs in the Union, they'll just be on and pulsed "randomly". I believe I can achieve this effect by wiring them to the outputs of the 4017s according to the random number sequence I have generated with a generator I found on the internet. This will require a great many components. I don't know a better way. I do not wish to fool with a microcontroller. That is above my pay grade. I just want to have a bunch of chips, wires, and solder. Oh my.

View attachment 259961
Do you really intend to have ~2000 LEDs in that flag?
 

Ya’akov

Joined Jan 27, 2019
5,657
That is the plan. 1773 total. 84 in the short stripes. 132 in the long stripes. 93 blue in the Union and 300 in the stars.

0.020 mA per LED is a lot of mA. It can be done.
20mA is the usual expected dissipation for a normal, 5mm LED. If you have 1773 (add three more, don’t miss out on that chance) you will be dissipating 20mA x 1773 = 35.5A.

That’s a lot of power and doesn’t account for the enormous number of discrete logic ICs you plan to use. I certainly don’t want to be discouraging, but the scale of this seems really over the top. Even though it would require learning, using an MCU with addressable LEDs would make your life a lot easier. It still wouldn’t change the scale, though.

This seems like a project for literally years of effort unless you plan on putting in 40 hour weeks on it.

In any case, however you do it, make it modular. Design modules that can be used in arbitrary chains to reach the numbers you want. Don’t set out to make it monolithic. Modules will make design, building, and repair much easier.

I hope you manage to work it out.
 

Thread Starter

William A Rose

Joined Feb 5, 2022
45
20mA is the usual expected dissipation for a normal, 5mm LED. If you have 1773 (add three more, don’t miss out on that chance) you will be dissipating 20mA x 1773 = 35.5A.

That’s a lot of power and doesn’t account for the enormous number of discrete logic ICs you plan to use. I certainly don’t want to be discouraging, but the scale of this seems really over the top. Even though it would require learning, using an MCU with addressable LEDs would make your life a lot easier. It still wouldn’t change the scale, though.

This seems like a project for literally years of effort unless you plan on putting in 40 hour weeks on it.

In any case, however you do it, make it modular. Design modules that can be used in arbitrary chains to reach the numbers you want. Don’t set out to make it monolithic. Modules will make design, building, and repair much easier.

I hope you manage to work it out.
Each stripe will be its own circuit as will the Union and the stars. I will find a way to add 3 more! It's gotta be right! Any guidance, in layman's terms, is appreciated. I will be drawing this and testing each circuit on a breadboard before I build anything. I have been working on this for 2 years (sort of).
 
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