apessos's New Writeupshttp://everything2.com/?node=New%20Writeups%20Atom%20Feed&foruser=apessos2003-09-02T17:30:38Zfrequency divider (idea)http://m.everything2.com/user/apessos/writeups/frequency+dividerapessoshttp://m.everything2.com/user/apessos2003-09-02T17:30:38Z2003-09-02T17:30:38Z<p>A frequency divider takes a frequency and slows it down. How much depends upon how you use the frequency divider. There are many ways to create a frequency divider. You won't use them all, but just remember that each has its own advantages and disdavantages.</p>
<p>There are chips that are made specifically for frequency division, <a href="/title/FPGA">FPGAs</a> can use code to divide frequencies, and there are a handful of other ways using simple logic. The way that will be described here will use a <a href="/title/D+flip-flop">D flip-flop</a>, as that's where a frequency divider was mentioned.</p>
<p>For this example we are going to take a 2MHz clock and divide it down to 1MHz. This is only for illustrating how to do frequency division with a <a href="/title/D+flip-flop">D flip-flop</a>.</p>
<pre>
_______
| |
--|D Q|--
| _|
--|CLK Q|--
-------
</pre>
and connect it as shown below.<br>
<pre>
/------------------\
| _______ |
| | |<!-- close unclosed tag --></pre>…D flip-flop (idea)http://m.everything2.com/user/apessos/writeups/D+flip-flopapessoshttp://m.everything2.com/user/apessos2003-08-29T19:06:15Z2003-08-29T19:06:15Z<p>D <a href="/title/flip-flops">flip-flops</a> are much like ice cream, they come in many different flavors. And regardless of the flavor you have, it's still a D <a href="/title/flip-flop">flip-flop</a>.</p>
<p>We are going to look at a simply D flip-flop first. The other flavors just build off the basic one.</p>
<br>
<pre>
\Enable
|
_______|_______ <a href="/title/Truth+Table">Truth Table</a>
| | ----------------------
D | | Q D CLK Q \ENABLE
----| |---- ----------------------
| | H ^ H L
| | L ^ L L
| | X L Q L
| 74LS374 | X X L H
CLK | | ----------------------
----| | X = Don't care
| | ^ = LOW to HIGH transition
|_______________| H - HIGH (voltage)<!-- close unclosed tag --></pre>…Pull-up resistor (idea)http://m.everything2.com/user/apessos/writeups/Pull-up+resistorapessoshttp://m.everything2.com/user/apessos2002-02-20T21:28:21Z2002-02-20T21:28:21Z<p>Formerly known as <b>The Black Art of Pull-Up Resistors</b></p>
<p>Well, it's not really a black art, but pull-up <a href="/title/resistor">resistors</a> are one of those concepts that seem to get glossed over in <a href="/title/college">college</a>. It is important to know when to use pull-up <a href="/title/resistor">resistors</a> in a design and why. That is what I will talk about in this node.</p>
<p>Before I continue, I want to define the symbol below as a switch. It can either be open or closed.</p>
<pre>
/
____/ -----
SWITCH
</pre>
<p>It is helpful to understand what happens in a design when there are no pull-up <a href="/title/resistor">resistors</a>. Shown below is a small chip connected to a switch. When the switch is closed, the first pin of the chip is connected to ground.</p>
<pre>
/ -------
_____/ -------| |---
| ---| |---
| ---| |---
\ / -------
GND
</pre>
<p>However, when the switch is open, the signal is not connected<!-- close unclosed tag --></p>…open collector (thing)http://m.everything2.com/user/apessos/writeups/open+collectorapessoshttp://m.everything2.com/user/apessos2001-04-23T23:33:33Z2001-04-23T23:33:33Z<p>These beauties are the basic building blocks of NANDs, NORs, and NOTs. And understand them not only puts you on your way to becoming a great engineer but you can impress your friends with terms like "collectors", "emitters" and "bases"!</p>
<p>An open collector is just a <a href="/title/BJT">BJT</a> with the emitter grounded. The collector is left floating or unattached to anything hence it is called an open collector.</p>
<p>The key to understand this circuit is realizing when there is no voltage applied to the base of the <a href="/title/BJT">BJT</a>, no current can flow from the collector to the emitter. When a voltage is applied to the base, the <a href="/title/BJT">BJT</a> turns on, allowing current to flow from to the collector straight throught the emitter and right to ground.</p>
<p>Now, if a voltage is just connected to the collector, let's just pick 5 volts, when the <a href="/title/BJT">BJT</a> is turned on, that 5 volts is going to flow right through the collector, straight through the emitter and will go right to ground. Thus creating a short circuit, the <a href="/title/BJT">BJT</a> will<!-- close unclosed tag --></p>…equivalent resistance (idea)http://m.everything2.com/user/apessos/writeups/equivalent+resistanceapessoshttp://m.everything2.com/user/apessos2001-04-19T18:26:30Z2001-04-19T18:26:30Z<p>Equivalent resistance is a handy thing to know in a few situations. One situation is when your college professor is testing your knowledge on equivalent resistance and you want to pass. In this instance, you will have to reduce a confusing circuit filled with lots of resistors down to a circuit with fewer resistors. And then you solve lots of equations on this smaller circuit. However, in real life, this rarely happens.</p>
<p>What will be more likely, however, is to connect two resistors in series or parallel to get a desired resistance. For example, for a hobby project I was working on, I needed a 130 ohm resistor and I couldn't find any at Active Electronics, my local electronics shop. But they had plenty of 260 ohm resistors. Putting two of them in parallel got me 130 ohms and my circuit worked great. </p>
<p>It might seem silly, but resistors don't come in every value you need, despite how many letters you write to the manufacture. If you can't find the exact resistance you need, you have a<!-- close unclosed tag --></p>…vegan (idea)http://m.everything2.com/user/apessos/writeups/veganapessoshttp://m.everything2.com/user/apessos2001-04-18T21:16:08Z2001-04-18T21:16:08Z<p>A person who chooses not to using or consume any <a href="/title/animal">animal</a> products. This includes <a href="/title/meat">meat</a>, <a href="/title/dairy">dairy</a> and <a href="/title/eggs">eggs</a>. They also avoid <a href="/title/fur">fur</a>, <a href="/title/leather">leather</a>, <a href="/title/wool">wool</a>, <a href="/title/down">down</a> or any other material made from animals.</p>
<p>Most have strong tendencies towards protecting the <a href="/title/environment">environment</a> and not causing <a href="/title/harm">harm</a> to <a href="/title/animal">animals</a>. Some vegans are strong advocates of promoting a cruelity-free and healthy lifestyle while others are not. But not all vegans are animal rights activities, as some are most focused on the health benefits. And evidence is mounting linking the consumption of <a href="/title/animal">animal</a> fats and <a href="/title/protein">proteins</a> to heart disease, colon and lung cancer, and osteoporosis to name a few. But this is still being debated and each side has research and case studies which support their case, respectively.</p>
<p>There is much opposition to this belief causing a heated debate on either side of the issue. Many people consider vegans to have a misplaced empathy towards <a href="/title/animal">animals</a> and cite reasons why humans<!-- close unclosed tag --></p>…