Basic schematics question

[fancypete]

Edit 1/31/2021: This article answered a lot of my confusion:

Breadboard A Vintage Distortion

Original post:

This is really basic I'm sure, and I'm almost embarrassed to ask. I really enjoy trying to understand how the signal is flowing through each circuit I put together. I try to match the diagram in the build docs to the physical board as I assemble it. But one thing confuses me: Why do the schematics have a separate diagram for the foot switches? Among the pedals I've built, there are similarities in these switch diagrams (4k7 resistors before the leds, a diode, one or more capacitor), but there are variations as well. Why are some configurations different? Wouldn't one foot switch configuration work for every circuit? And why aren't they drawn attached to the effect circuit?

I've googled it and the best I can find is that a lot of basic parts of circuits are assumed, and therefore omitted from the schematics. For hobbyist electronic enthusiasts such as myself, it's confusing. Can anyone recommend a good book or resource I could learn more about interpreting these schematics? There are so many to choose from. Thanks!

 

[giovanni]

Do you have two examples to compare so we can discuss specific differences?
Electronic circuits are very complicated with a lot of parts and technical requirements. So it helps to separate concerns somewhat. That’s why you usually see the main signal circuit schematic to be separate from other things like power filtering, biasing and switching. It’s an attempt to simplify your life, not make it harder. The best advice I can give you is to ignore the parts of the circuit not currently relevant: when you’re looking at the main signal path, you don’t necessarily want to be distracted by details of how the power is filtered and so on.
I hope that makes sense!

 

[fig]

Hi Pete,

These might prove useful. They have been a good reference source for me. Also, there are quite a few experts on this forum that are an invaluable source.

Small Signal Design

Practical Audio Electronics

 

[Robert]

At least for the majority of the circuits here the footswitch wiring isn't part of the PCB, so it isn't included in the schematic.

It was done this way for a "modular" approach. You might want to use a 3PDT footswitch, relay bypass, buffered bypass, in some cases no bypass, you might be building it into a 2-in-1 pedal, or a Eurorack.

Depending on where the indicator LED is located on the PCB it might be more efficient to place the current limiting resistor on the anode (or cathode) side.

 

[zgrav]

Hi Pete,

These might prove useful. They have been a good reference source for me. Also, there are quite a few experts on this forum that are an invaluable source.

Small Signal Design

Practical Audio Electronics

I suggest checking with your local library to check out an introductory text on circuits and electronics. For the links above, you can read some a surprising amount of those books using the "Look Inside" option for them. on the linked page.

 

[fancypete]

The modular approach makes sense. Thanks for the replies and book recommendations.

 

[giovanni]

Those are nice recommendations! Haven’t seen them before. I’ve been going through the Art of Electronics which is very comprehensive but probably more theoretical than those.

 

[Chuck D. Bones]

I was not impressed by The Art of Electronics. It tries to cover too many topics without nearly enough depth on most of them. It's the kind of book you leave out on the coffee table to impress your non-technical friends.

I recommend this book:

 

[fancypete]

I recommend this book:

..yeah but that's an above average dog. I'm just a regular dog. Proof: I actually googled the title.

 

[fig]

Gotta say though, reading posts here have proven more valuable and educational.

 

[phi1]

For foot switches, I think this is a nice article for explaining the background.

https://www.madbeanpedals.com/tutorials/downloads/MBP_FootswitchWiring.pdf

His diagram is a little different than pedalpcbs, but it does the same thing.

 

[Chuck D. Bones]

Great article, well written.

 

[fancypete]

Thanks for all the great reading material. I've looked it over and I still have some questions.

Here is an example of my confusion:


I know that VCC is the common voltage source, and that the three line arrow is the ground. I know that the LED is wired to the switch and that R100 is the CLR. What are D100 and C100 for? I'm also confused by the + and - circles on the switch diagram, and how they connect to the circuit. My best deduction is that the SW is essentially like the IN and the + and - must be referring to the jack? This further confuses me because my builds have the + from the jack connected directly to the switch with no diode/capacitor voodoo in-between. If you were to make an "always on" pedal, would you even need those components?

I'm totally stumped by the shorthand symbols and implied connections. I haven't been able to find a good answer by reading (I've tried!). How do these schematics interface with eachother in the real world? I hope this is a conceptual hurdle that I will be glad to be over soon! Thanks for your help everyone.

 

[Chuck D. Bones]

The + and - circles are where the board connects to the power jack. There is a pad marked + and a pad marked - on the board, near the center along the top edge. Those schematic symbols represent those pads.

D100 is reverse polarity protection. Sooner or later, every one of us has or will connect the power to the board backwards. That diode prevents catastrophic failure if the power is reversed. Some builders do it differently or not at all.

C100 is a power filter. Not absolutely necessary is you run the pedal on batteries, but essential if you use a DC power supply because there is always some amount of noise on the DC power. Nothing magic about 100uF, it's just the most commonly used value for that purpose.

 

[fancypete]

Ok so if the VCC would be like the + rail on a breadboard and the ground would be the end of the - rail, would D100 just be between the + from the jack and the + rail? Getting closer

 

[Chuck D. Bones]

Yes. Are you building a breadboard?

 

[fancypete]

Yes. Are you building a breadboard?

Yes. Are you building a breadboard?

I'm planning to. There were lots of examples on breadboard in the literature linked to above, but they didn't look exactly like the schematic shown.

I figure the only way to learn is to try to construct a circuit from the schematic. I just ordered my first breadboard and can't wait to start some hands on learning.

 

[Chuck D. Bones]

Start with something simple, like a Rangemaster or Fuzz-Face. Breadboard can be rewarding and frustrating, sometime both at once! You will become very familiar with Bill's Law. Make sure you have a DMM and know how to use it.

 

[fig]

@fancypete

Please consider starting a thread and sharing your project and experiences with others. Your learning curve may provide an easier path for someone else.

 

[giovanni]

I was not impressed by The Art of Electronics. It tries to cover too many topics without nearly enough depth on most of them. It's the kind of book you leave out on the coffee table to impress your non-technical friends.

Interesting. In college I used Sedra Smith which was ok. I was looking for a refresher and thought that might do it.