The value depends on the application.
You just haven't seen enough circuits. I've used caps ranging from 1uF to 470uF. Electrolytic capacitors typically have a wide tolerance which will affect timing. With large electrolytic capacitors, you also need to factor in leakage current.

National Semiconductor included this graph in their datasheet:
View attachment 260457
It only goes up to 100uF, but larger caps can be used.

Thanks, but that didn't help much. I want to know why I should choose a particular capacitor and why. For these LED projects, the snowflakes will have up to 24 LEDs. That flag is super ambitious and may not be feasible as I envision it. I am sure hoping I can pull it off. Anyway, the timer circuit, as I understand it, just serves to make the 4017s advance. It isn't driving anything but a 4017 counter advance. I suppose even the smallest capacitor would suffice for that. I don't think there were any capacitors in the cascaded 4017s circuit. I don't see a need for them. Not even for the pulsing of the LEDs in a "random" fashion as I envision it. I'll get something drawn up for everyone's review (and hopefully only constructive criticism) soon. I have a lot going on right now and progress is slow. I sure do appreciate the responses.

 

#20 is a little too thick. The boards were designed for #22 solid and 0.025" square headers fit well. I've seen some people advising to not use them because they're too wide (just another old wives' tale). They're not if oriented square to the contact faces; the diameter of #22 wire is 0.0253".

I check continuity...


View attachment 260375
Hate to have to be the one to break it to you, but these devices are packaged improperly. If they aren't outright dead, they could be unreliable.

Any CMOS IC's are static sensitive as are some blue and white LEDs and need to be handled, packaged, and stored properly. CMOS IC's include protection diodes, but they're only tested to a couple thousand volts and aren't intended to provide protection from flagrant abuse.

Were we supposed to be able to see the markings?
View attachment 260376
Unless TI changed their marking methodology for NE555P, I'd be suspicious of them.

The discoloration on the leads of the top device looks suspicious:
View attachment 260377

The 20 AWG jumpers came in today. They fit perfect in the breadboards. I am so happy happy happy.

 

They fit perfect in the breadboards.

That's the maximum diameter breadboards are designed for and a bit too snug for my taste. 3M recommends using #22 (page 4 of the attached brochure - note that they have a typo and have 0.32" when they meant 0.032").

Stressing the contact clips will impact the ability to make good contact with smaller diameter leads. I've seen some saying to not insert 0.025" male headers and to not use the contacts by the channel for anything except IC leads.

The leads for TO-220 are 0.005" larger than #20 wire and I've been twisting them 90 degrees so they're 0.015".

https://www.allaboutcircuits.com/news/the-best-wire-for-breadboarding/

 

I want to know why I should choose a particular capacitor and why.

It would be helpful if you posted a schematic and asked specific questions.

Anyway, the timer circuit, as I understand it, just serves to make the 4017s advance. It isn't driving anything but a 4017 counter advance. I suppose even the smallest capacitor would suffice for that.

In your application, the 555 is providing the clock signal for the counters. You select the capacitor and resistor values based on the frequency you want.

The datasheet shows how to calculate the on and off times (periods). Frequency is the reciprocal of the total time period.

I don't think there were any capacitors in the cascaded 4017s circuit. I don't see a need for them.

With many schematics for digital circuits, decoupling caps are assumed. Their function is to prevent switching noise from getting on the power rail and causing difficult to debug problems. 0.1uF ceramic caps are commonly used. For higher frequency circuits, you may require a combination of 0.01uF and 0.1uF caps for good decoupling.

Some put one across the power pins of each IC. You can even buy IC sockets with integral decoupling caps. I tend to use fewer.

 

That's the maximum diameter breadboards are designed for and a bit too snug for my taste. 3M recommends using #22 (page 4 of the attached brochure - note that they have a typo and have 0.32" when they meant 0.032").

Stressing the contact clips will impact the ability to make good contact with smaller diameter leads. I've seen some saying to not insert 0.025" male headers and to not use the contacts by the channel for anything except IC leads.

The leads for TO-220 are 0.005" larger than #20 wire and I've been twisting them 90 degrees so they're 0.015".

https://www.allaboutcircuits.com/news/the-best-wire-for-breadboarding/

Hmmm. At least breadboards are not terribly expensive.

 

It would be helpful if you posted a schematic and asked specific questions.
In your application, the 555 is providing the clock signal for the counters. You select the capacitor and resistor values based on the frequency you want.

The datasheet shows how to calculate the on and off times (periods). Frequency is the reciprocal of the total time period.
With many schematics for digital circuits, decoupling caps are assumed. Their function is to prevent switching noise from getting on the power rail and causing difficult to debug problems. 0.1uF ceramic caps are commonly used. For higher frequency circuits, you may require a combination of 0.01uF and 0.1uF caps for good decoupling.

Some put one across the power pins of each IC. You can even buy IC sockets with integral decoupling caps. I tend to use fewer.

Definitely some good info in this post. I don't know what frequency I'll settle on. I hope to be able to actually see the circuit in operation and make adjustments to find the right effect. Keep in mind, I have no real idea what I am doing. That makes it more tedious than it probably needs to be, but it is fun.

 

At least breadboards are not terribly expensive.

If you abuse the contact springs, you could waste a lot of time troubleshooting intermittent connections. I used to use #24 wire because I had a lot of CAT5 cable. I decided that it wasn't worth having wires that dislodged too easily and bought a couple 1000' reels of solid #22 wire.

Back in the 70's, I was paying $10 or more for high quality breadboards (there were no Chinese knock-offs back then).

I don't know what frequency I'll settle on.

0.1uF ceramic caps will be sufficient for any frequencies that you'd use for CD4017.

 

puncitation

punctuation?

 

I have this. I am going to build my circuits to test them on it.

This is what I do for breadboards that have a break in the power rails:

I used #22 wire on this breadboard, but I've also used component leads.

You can remove one of the power rails when you connect boards. If you attach them to a substrate, you can run some of the spare rails perpendicular to the breadboards for convenient power distribution:

These breadboards don't have split power rails.

 

Which page of this thread has the schematic of all those resistors and unmarked transistors and ICs?