# Basic schematics question



## fancypete (Jan 24, 2021)

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





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						Breadboard A Vintage Distortion
					





					diy.smallbearelec.com
				




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!


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## giovanni (Jan 24, 2021)

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!


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## fig (Jan 24, 2021)

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


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## Robert (Jan 24, 2021)

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.


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## zgrav (Jan 24, 2021)

fig said:


> 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.
> 
> ...



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.


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## fancypete (Jan 24, 2021)

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


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## giovanni (Jan 24, 2021)

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.


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## Chuck D. Bones (Jan 24, 2021)

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:


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## fancypete (Jan 24, 2021)

Chuck D. Bones said:


> I recommend this book:


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


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## fig (Jan 24, 2021)

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


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## phi1 (Jan 24, 2021)

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.


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## Chuck D. Bones (Jan 25, 2021)

Great article, well written.


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## fancypete (Jan 29, 2021)

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.


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## Chuck D. Bones (Jan 29, 2021)

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.


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## fancypete (Jan 29, 2021)

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


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## Chuck D. Bones (Jan 29, 2021)

Yes.  Are you building a breadboard?


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## fancypete (Jan 29, 2021)

Chuck D. Bones said:


> Yes.  Are you building a breadboard?





Chuck D. Bones said:


> 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.


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## Chuck D. Bones (Jan 29, 2021)

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.


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## fig (Jan 30, 2021)

@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.


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## giovanni (Jan 30, 2021)

Chuck D. Bones said:


> 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.


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## Chuck D. Bones (Jan 30, 2021)

Maybe I was a little harsh.  As a refresher, AoE might be fine.

When I was in school, the text books were all pretty dry.  Long on theory, short on applications.  Best instructor I had was a retired Navy electrical engineer.  His lectures were all about practical applications.


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## fancypete (Jan 31, 2021)

This article had the exact information I was confused about.  Can't believe I missed it.  I'm absolutely sure it's linked to elsewhere in this forum, but in any case, here it is:





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						Breadboard A Vintage Distortion
					





					diy.smallbearelec.com
				




Hope it helps someone else!  I'll add it to OP as well.


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## Grubb (Feb 7, 2021)

Chuck D. Bones said:


> 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.


How do the + and - circles relate to VCC in that diagram? Is VCC representing an output in that stage and then an input 4 times (R3, R6, R8 and Q1) in the top section of the schematic?


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## phi1 (Feb 7, 2021)

The + and - are the solder pads for the wires to the dc jack.

Vcc is approximately 9vDC that powers the circuit. The diode in between + and Vcc is to block reverse voltage, so other components in the circuit wouldn’t be damaged if you plugged in the wrong supply. I said approximately 9vDC because the diode will cause a very small voltage drop (I think around 0.2-0.3v) from the + to Vcc.


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## Nostradoomus (Feb 7, 2021)

Think of all the VCC pins as having a trace from the power supply to those points, it’s just a lot easier and cleaner to make them pin points in the schematic.


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## zgrav (Feb 7, 2021)

Chuck D. Bones said:


> Great article, well written.


it is a fun and informative journey with the bean.


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