(If you are not solid on voltage/ current/ resistance, please sonciser reading my page about them.)
This page has been written in haste. Diagrams, etc, to come... if I gt any indication that anyone is READING it!
I've said this is a page about "intermediate" digital electronic signals.
Forgive me a very fast recap of some basics?
"Digital" is a bad name. Digital electonics is when only two volages matter.
Often they are called "zero" or "ground" and "one".
If you know what "everyone" knows, you will understand that "zero" means "CLOSE ENOUGH" to zero to COUNT as "zero".
"One" will often mean "near 5v" or "near 3.3 volts" (often written "3v3")
You don't want a voltage in your digital electronics circuit ABOVE some nominal "top" voltage; you don't want a voltage ABOVE that... but often we are calling 5v or 3v3, or whatever voltage is being used, is really only "near" that "other" voltage. (Sometimes called Vcc or Vdd.
You really don't need to worry about all of that too much!
In digital electronics, you will have inputs and outputs.
INPUTS: You connect a "high" (i.e. 3v3, or 5v, or whatever the circuit is using for "high" or "one") to an input, and VERY LITTLE CURRENT FLOWS! But the circuit "knows" you have connected that voltage.
OR you connect a wire betweem the input and the "ground" end of the power supply or battery. Again- very little current flows, but the circuit "knows" the connection is there.
It is a Bad Idea to leave an input connected to NOTHING. The input is said to be "floating". "Pull-up" resistors are the answer! (Or pull-down resistors.) When you work with Arduinos, you can even "connect" a pull-up resistor that is inside the chip in your Arduino... or not... as suits your needs this day.
OUTPUTS: Outputs can be make "high" or "low". When they are high they are as good as... up to a point... a wire connected to the "high" end of your power supply or battery.
When they are low they are as good as... up to a point... a wire connected to the "ground" (aka "zero volt") end of your power supply or battery.
What many things do depends upon the LEVEL seen, at the moment, on an input. Your desk lamp is a "level driven" device. While there is a high voltage applied to the bulb, it is on. When it is absent, the bulb is off. (In desklamps, the input would probably be "floating"... allowed in desk-lamps, not a good idea in digital electronics.)
But some devices are more clever. They react to a CHANGE in the "state" (or "level" or voltage) applied to the input.
These devices are said to be edge sensitive. They are so clever that they usually respond only to one or the other of the possible "edges".
If what's connected to the input has gone from low to high, the input is said to have experienced a "positive", or "rising" edge.
If what's connected to the input has gone from high to low, the input is said to have experienced a "negative", or "falling" edge.
(If an input has a pull-up resistor on it, connecting a low output from somewhere to the input will "drive the input low". If you disconnect the output, you might think "Oh! That's now floating, right?" Well, no. You would have beenm right to remember that inputs should have something connected to them. But when the low output was disconnected from the input, the pull-up resistor "counted" again, and because it is there, for our intents and purposes, the input is being "driven high", as if a high output was connected to it.)
That, I hope, will be enough to serve those who need it in the course of reading another page I am working on just now!
If you found this of interest, please mention in forums, give it a Facebook "like", or whatever. If you want more of this stuff: help!? There's not much point in me writing these things, if no one hears about them. Does anyone feel they are of any use? If YOU do- please spread the word!
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It's both! Flat-Earth-Academy.com is something I started years ago. For a variety of reasons, I can't offer you httpS:// access there. (As you are not asked to input any information, that's moot, but it "worries" search engines.) So I'm moving to my new, all singing, and will do the httpS:// dance site, "WYWTK.com", and Flat-Earth-Academy is gradually acquiring pages there. (Well, HERE, as what you are reading is one of my "wywtk/fea" pages.)
Why "WYWTK"? It comes from "What You Want To Know".
Page has been tested for compliance with INDUSTRY (not MS-only) standards, using the free, publicly accessible validator at validator.w3.org. It passes in some important ways, but still needs work to fully meet HTML 5 expectations. (If your browser hides your history, you may have to put the page's URL into the validator by hand. Check what page the validator looked at before becoming alarmed by a "not found" or "wrong doctype".)
AND tested for
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