Explanation of SifuF's volume control diagram


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I posted this on BH, but as per a request, here she is on good ol Modretro!

I noticed that a lot of people were scared and confused by this diagram. No need to be :) !!!

Essentially, you are looking at the building blocks of the electronic world. What you see in the picture below are "logic gates." The half circle is an AND gate. In noob terms, the AND only allows voltage to flow through it if both inputs are activated.

Keep in mind: these are symbols not physical drawings of gates. All you need to know is that these gates are inside of IC chips - that is how you will use them.


Thus, pushing "start" AND the "up" button will allow voltage to go to the "volume up" area. "Start" AND the "down" button will allow voltage to go to the "volume down" area.

The triangle with a circle on the end is a NOT gate. It reverses the high/low flowage. In noob terms: this gate makes sure that voltage will go to the AND gate. Why do you need it? Because when you push the "start" and "up" button, you are connecting ground to the AND gate.

AND gates don't like ground very much. In fact, they hate ground so much that no voltage will pass through the AND gate unless both of their inputs are "high" (basically not ground). So the NOT gate turns that ground into a voltage signal (high) that can then pass through the AND gate.

SifuF was also kind enough to give us the names of the IC chips that peform AND and NOT functions.

Here's what is going on inside of an AND IC chip (known as the "4081 series"). This picture is what allowed me to understand this crap:

In the above pic, Vss is ground and Vdd is power (if I have that backwards then let me know).

See my second post for info on the NPN logic.

These chips are EXTREMELY helpful even though they are kinda basic compared to billion transistor chips. But these chips can give you a lot of cool ways to program your portable. Volume control, as seen above, is a great example. Think about when you use SNES emulators on a PSP. You have to press several buttons to get to the menu. That is AND gates in action.

- If you were really crazy, you could even program your portable to switch between battery and power cord at the press of a button (although that would require plugging in the power cord before hand)
- OR you could program the fan in your portable to shut off to save power (you would have to live in either Canada or Wisconsin for this mod :p )
- program a switch between PS1 screen and TV screen
- program a switch between gaming platforms if your portable was multi-platform
- program a reset button combo (ex: start+Dpad left+L = reset system)
- screen brightness

^some of those would require more than AND gates, but hopefully it gets you thinking!

You get the idea! So gates are cool, no need to think of them as "too much work". I mean we portablize so even AP exams aren't too bad these days :p
Erlex said:
Good work on explaining some basic circuit theory. As stated, a lot are turned off by it when it isn't nearly as hard as it looks.

The NPN - 2N3904 is the type of discrete transistor that he used. This one works by passing a signal from the collector, to the emitter when the base is high (can be thought as on/when voltage is applied/binary 1). See picture.

I don't want to high jack your explanation or anything, but here is a visual explanation of pretty much what Tchay said. This is for the case up turning the volume UP. Remember, the diagram is a logic diagram, the symbols are not physical components.

This is when no button is pressed.

This is when the start button and the up button are pressed.

Maybe that will make it a little more clear ;)

EDIT: Fixed my silly logic mistake.