I want to light up an LED with 220 VAC using least components. These two circuits come to mind:    R1, R2 will be around 200K - 300K depending upon the brightness that I will need. Not much brightness is required so I can even go higher if I am able to get some amount of light out of the LED.  Which one (if any) will work?  (I am not much concerned with efficiency as these will be used as indicators when a high power device is turned on. For ex - a geyser. This circuit will be wired in parallel with the geyser to accomplish that. If I use 200K resistor, I'll be using up around 0.25 watts which will be negligible as compared to 1000 watts being consumed by the main device.)
I'm attempting to build an LED bed lamp that will be powered by 240V mains. The LEDs are  which if I use with a 12V supply and have calculated correctly will draw 0.24W each. I plan to use 5 or 6 of them in the lamp so will consume a maximum of 1.5W.  Initially I thought I'd use a transformer and bridge rectifier to get the required 12V DC but the transformer weighs a ton and is too bulky. The next option was to use a  but I'm wondering is there is a better way?  I think it would be possible to power the LEDs directly from mains using only a rectifier without mains and stepping down the voltage but then it's not safe. Are there any smallish components that can both isolate the mains and supply a DC voltage?
Problem Currently, I am playing on a server where hoppers transport items at the rate of 64 items a second, and this has proved very difficult to build a sorter for. I'm not at all proficient in Redstone building but have tried building basic sorters and ones that I have found on YouTube and I haven't gotten anything to work. Solution Hopefully one of you is really good at Redstone and can help me design a sorter that can work under these conditions. (I need the sorter that can sort items while I AFK kill witches with a looting 47 sword P.S. most of the problem is with the sorter itself because no items will stay in the sorter hopper (bc the whole stack goes into the chest so the hopper doesn't have anything to go off of to sort) so any solution to that would be helpful as well. How To Recover My Data From Not Detected Hard Disk? I am using Acer Laptop one day before my Hard Disk is not detected in BIOS and not booting it's shows Insert Boot Disk and I am try another H.D.D it's boot perfectly in my Laptop but,I want detect and recover my data on not detected hard disk. I am not experience about Hard Disk please, can any one help me how to recover my data from not detected Hard Disk. Selectively coloring text in RichTextBox How can I paint in red every time I meet the letter "A" in RichTextBox? Possible Duplicate:             Each post has an indicator which summarises who the post is shared.    What is the difference between these two terms? Should I write summarises or summarizes? What is the most concise and efficient way to find out if a JavaScript array contains a value? This is the only way I know to do it: function contains(a, obj) {     for (var i = 0; i &lt; a.length; i++) {         if (a[i] === obj) {             return true;         }     }     return false; }  Is there a better and more concise way to accomplish this? I have a Python script which I would like to execute at every startup. I can run it by adding this to the startup applications:  python3 /path/to/script.py   That works, but it doesn't open a terminal window, so I can't see the program's output. How could I make it open a terminal window and execute the script in there?  Note: I get the window to stay open with input(' ') at the end of the Python script. Thanks! Let f(t)=2/(t+8)  (a) Simplify the following difference quotient as much as possible: $$[f(t+h)−f(t)]/h$$  MY ANSWER (CORRECT): $-2 / [(t+8)(t+h+8)]$  (b) Use your result from (a) and the limit definition of the derivative to calculate $f′(t)=\lim_{h → 0} [f(t+h)−f(t)]/h=$  MY ANSWER (CORRECT): $-2 / [(t+8)^2]$  (c) Use your answer from part (b) to evaluate $f′(−3)$  MY ANSWER (CORRECT): $-2 / 25$  (d) Find the equation of the tangent line to the curve at the point $(−3,f(−3))$ y=  I have tried the point-slope formula, $y-y_1=m(x-x_1)$, but my answer was incorrect. How can I link to an external resource in a community-friendly way? I would like to help my fellow Stackizens, using material from my blog or other website.  But external links are sometimes viewed as excessive promotion.  From the FAQ:     Be careful, because the community   frowns on overt self-promotion and   tends to vote it down and flag it as   spam. Post good, relevant answers, and   if they happen to be about your   product or website, so be it. However,   you must disclose your affiliation in   your answers. Also, if a huge   percentage of your posts include a   mention of your product or website,   you're probably here for the wrong   reasons.   I have tried posting answers that reference my blog, and I have followed the above rules, but my answers still get flagged as spam.  How can I craft an answer that references my blog, website or other resource, but is still acceptable to the community? L293, L298 and SN754410 H-bridge drivers on low voltage power supply Using PTSerif-TLF for Cyrillic with TeX Gyre Pagella Let $f_1 , f_2: I\mapsto \mathbb{R}$ bounded functions. Show that $L(f_1)+L(f_2)\leq L(f_1+f_2)$ (Riemann integral) Let $f_1 , f_2: I\mapsto \mathbb{R}$ bounded functions. Show that $L(f_1)+L(f_2)\leq L(f_1+f_2)$ where $L(F)$ is the supremum of the lower sums of the Riemann integral.  I tried to by contradicction $L(f_1)+L(f_2)&gt; L(f_1+f_2)$ and isoleting $L(f_1)&gt; L(f_1+f_2)-L(f_2)$ and usig the definition of sup.  I also tried to use $\sup(A)+\sup(B)=\sup(A+B)$ but it din't work.  Thanks. Wifi disabled, no hardware switch available, rfkill list reads "Hard Blocked" anyway on an Acer Aspire One I have got codes like the following (generated by Kile). How can I add a caption. I guess I should have used the table environment. Is there any solution now?  \newcommand{\mc}[3]{\multicolumn{#1}{#2}{#3}} \begin{center} \begin{tabular}{rccll}      &amp;   &amp; \mc{3}{c}{Colin}\\      &amp;   &amp; a &amp; \mc{1}{c}{b} &amp; \mc{1}{c}{c}\\\cline{3-5} Rose &amp; \mc{1}{c|}{A} &amp; \mc{1}{c|}{(1,2)} &amp; \mc{1}{c|}{(2,5)} &amp; \mc{1}{c|}{(4,4)}\\\cline{3-5}      &amp; \mc{1}{c|}{B} &amp; \mc{1}{c|}{(7,4)} &amp; \mc{1}{c|}{(3,5)} &amp; \mc{1}{c|}{(0,6)}\\\cline{3-5} \end{tabular} \end{center} Programming pattern to generate VGA signal with micro-controller? can you help me to do a difference of CDF? I have 2 CDF's with equal number of points that I want to compare. These are from:   Temperature of 1 month from 2012 Mean temperature across months   What can I do to obtain this difference, this is from the formula of Finkelstein-Schafer I have the following code:  if ($_POST['submit'] == "Next") {     foreach($_POST['info'] as $key =&gt; $value) {         echo $value;     } }   How do I get the foreach function to start from the 2nd key in the array? I have this statement and I need to say if it is true or false:  Let $\{a_n\}$ be a real sequence.  $$\lim_{n\to +\infty} a_n = 0 \quad \implies \quad \sum_{n=1}^{\infty}(-1)^na_n \quad \text{converges}$$  I know, from the Leibniz criterion that:     If $a_n \to 0$, $a_n$ is decreasing and positive then $\sum_{n=1}^{\infty}(-1)^na_n$ converges   From this fact I believe that the statement is false but I couldn't come up with an infinitesimal sequence that isn't decreasing and for that reason is divergent. I tried some function with $sin(\frac{1}{n})$ without any luck. Any help would be very appreciated, thank you! Fubini's theorem for series with dependent indices As a part of a proposition about power series that I am trying to prove I have to show that  $$ \sum_{m=0}^{\infty} \left(\sum_{n=m}^{\infty} \frac{n!}{m!(n-m)!}(b-a)^{n-m}c_n\right)(x-b)^m = \sum_{n=0}^{\infty}c_n(x-a)^n$$  Proof: What I have done so far is to show that  $$\sum_{m=0}^{n} \frac{n!}{m!(n-m)!}(b-a)^{n-m}(x-b)^m = (x-a)^n $$  So the next idea is to use Fubini's rearrangement theorem for infinite series (I have also shown that the series are absolutely convergent). However, the theorem does not accomodate for dependent indices. Intuitively (using triangular summation), I think that the proper way to interchange series would be \begin{equation*} %\begin{array}{ll} \sum_{m=0}^{\infty} \sum_{n=m}^{\infty} \frac{n!}{m!(n-m)!}(b-a)^{n-m}c_n(x-b)^m = \sum_{n=0}^{\infty} \sum_{m=0}^{n}\frac{n!}{m!(n-m)!}(b-a)^{n-m}c_n(x-b)^m %\end{array} \end{equation*} and thus  $$=\sum_{n=0}^{\infty} c_n(x-a)^n$$ However, I do not know how to perform this step rigorously in case of infinite summation. Why is it impossible to override a getter-only property and add a setter? Why is the following C# code not allowed:  public abstract class BaseClass {     public abstract int Bar { get;} }  public class ConcreteClass : BaseClass {     public override int Bar     {         get { return 0; }         set {}     } }      CS0546 'ConcreteClass.Bar.set': cannot override because 'BaseClass.Bar' does not have an overridable set accessor I am using nginx/0.7.68, running on CentOS, with the following configuration:  server {     listen       80;     server_name ***;     index index.html index.htm index.php default.html default.htm default.php;      location / {             root   /***;             proxy_pass   http://***:8888;             index  index.html index.htm;     }     # where *** is my variables   The proxy_pass is to a DNS record whose IP changes frequently. Nginx caches the outdated IP address, resulting in a request to the wrong IP address.  How can I stop nginx from caching the IP address, when it is outdated?