Control slot car with Arduino I'm brand new at electronics, and brand new at Arduino. I know very little about eighter, so please bear over with me... :-) To top it of, this is my very first post here on Electronics.  I'm working as a frontend developer, and my first Arduino project is about controlling a slot car via a website.  I can turn an LED on and off, remotely from a website, and I have connected the slot car to the Arduino, like I connected the LED, but of course there isn't enough power to get it running very fast. I does run, but sloooow... :-) I used a digital multi meter and saw that there were only 2V in the tracks, compared to 14.8V when plugged in the wall.  With my very limited knowledge of electronics, I was wondering if I could plug the slot car into the normal power socket, and somehow control how much power that goes into the tracks with Arduino.  How do I do that? With a resistor? Or?  Thank you in advance.
Arduino-controlled slot cars - alternative to MOSFETs for speed control? I'm attempting to control the speed of two slot cars in a set using Arduino.    Each car is controlled by a controller with a variable resistor that looks like this:    They're wired in parallel to the same 17V DC power supply:    Simplified:    For Arduino control, I experimented with manipulating a single car's speed using a MOSFET. It worked really well. Using a PWM output on the Arduino, I was able to pulse the MOSFET on and off to throttle the current and change the car's speed. The behavior of the MOSFET seemed to be exactly the same as the variable resistor controller; the resistance, voltage, and current fluctuated the same way on various parts of the circuit.  Enter car B. I added a MOSFET to the setup and mimicked the MOSFET wiring for car A, grounding them both to the Arduino ground. The result looks like this:    Here's a sketch:    Close up, MOSFET A:    MOSFET B:    At first, all seemed well. I sent signals to MOSFET A and successfully changed Car A's speed. I stopped Car A and pulsed MOSFET B, and I was able to control Car B's speed just fine.  Then, I turned Car B to a constant speed, and sent a signal to MOSFET A while Car B was still running. Car A started, but Car B's speed immediately dropped as a result of running Car A.  I hooked a multimeter up across the rails of Car B and watched its voltage while it ran on its own. Then, sure enough, when Car A started running alongside it, Car B's voltage dropped dramatically.  I figured this was because of my wiring configuration, so I left the multimeter on Car B, and made one change. I replaced MOSFET A with the original slot car controller:    I started running Car B again using its MOSFET. The multimeter showed a steady voltage, so I began to squeeze Car A's controller (the variable resistor), and Car A's speed increased. This time, however, unlike using a MOSFET to control Car A, the variable resistor did not affect Car B's voltage at all. Car B remained at a steady speed the whole time.  Any idea why this happens? The MOSFET seemed to function the same as the variable resistor (empirically) with a single car, but had totally different behavior with two cars in parallel. Is it because the MOSFET is not really changing resistance to current, but just switching it on and off, so it opens up another path for current to flow fully every time it closes? Is there an Arduino-controllable alternative to a MOSFET that would fluctuate actual resistance like the variable resistor? Digital potentiometer? Servo hooked up to a potentiometer? ;) I'm really curious what the difference is and what causes the major differences in behavior.
For a graph $G$, let $W$ be the (random) vertex occupied at the ﬁrst time the random walk has visited every vertex. That is, $W$ is the last new vertex to be visited by the random walk. Prove the following remarkable fact:      For the   random walk on an $n$-cycle, $W$ is uniformly distributed over all vertices different   from the starting vertex. html - how to remove right margin completely? I had a problem with disappearing marker as the data sum up to more than 100 while xmax was set to 100. See .  As written in the answer to the cited question I tried to avoid the problem by normalizing the value to 100. But this lead to (much smaller) rounding errors in previously correct rows and now the marker disappear there. See the following example. Before the normalisation the column F ist affected, after the column B.   How can I in a reliable way avoid this rounding problem? Or at least get a clear error message. I have quite a number of this plots and I don't want to have to check them all the time for missing markers.    \documentclass{scrreprt} \usepackage{pgfplots} \pgfplotsset{compat=1.13} \usepackage{pgfplotstable} \pgfplotsset{  my stackbar plot/.style={              xbar stacked,              xmin=0,xmax=100,              symbolic y coords={A,B,C,D,E,F,G},              ytick=data,              nodes near coords={xxx},}}  \begin{document}  \pgfplotstableread[col sep=space]{  text   --  -    +       ++  A      0.0 1.7 13.8    84.5  B      0.0 0.6 20.1    79.3  C      0.0 1.9 13.2    84.9  D      0.0 1.6 27.9    70.5  E      1.3 3.9 19.5    75.3  F      0.0 1.4 15.0    83.7  G      0.3 1.7 24.8    73.2  }\data   \pgfplotstablecreatecol[create col/expr={\thisrow{--}+\thisrow{-}+\thisrow{+}+\thisrow{++}}]{sum}\data %  \pgfplotstablecreatecol[create col/copy=--]{--o}\data  \pgfplotstablecreatecol[create col/copy=-]{-o}\data  \pgfplotstablecreatecol[create col/copy=+]{+o}\data  \pgfplotstablecreatecol[create col/copy=++]{++o}\data  \pgfplotstablecreatecol[create col/expr={100/\thisrow{sum}*\thisrow{--o}}]{--}\data  \pgfplotstablecreatecol[create col/expr={100/\thisrow{sum}*\thisrow{-o}}]{-}\data  \pgfplotstablecreatecol[create col/expr={100/\thisrow{sum}*\thisrow{+o}}]{+}\data  \pgfplotstablecreatecol[create col/expr={100/\thisrow{sum}*\thisrow{++o}}]{++}\data  \pgfplotstablecreatecol[create col/expr={\thisrow{--}+\thisrow{-}+\thisrow{+}+\thisrow{++}}]{sumnew}\data  \pgfplotstabletypeset[columns={text,sum}   ,precision=10,columns/text/.style={string type}]\data \quad \pgfplotstabletypeset[columns={text,sumnew},precision=10,columns/text/.style={string type}]\data   %\pgfplotstablesave{\data}{pgfplotstempout.dat} \begin{tikzpicture} \begin{axis}[my stackbar plot]  \addplot table [x expr = \thisrow{--o},y=text] {\data};  \addplot table [x expr = \thisrow{-o}, y=text] {\data};  \addplot table [x expr = \thisrow{+o}, y=text] {\data};  \addplot table [x expr = \thisrow{++o}, y=text] {\data}; \end{axis} \end{tikzpicture} \quad \begin{tikzpicture} \begin{axis}[my stackbar plot]  \addplot table [x expr = \thisrow{--},y=text] {\data};  \addplot table [x expr = \thisrow{-}, y=text] {\data};  \addplot table [x expr = \thisrow{+}, y=text] {\data};  \addplot table [x expr = \thisrow{++}, y=text] {\data}; \end{axis} \end{tikzpicture}  \end{document} Gameplay programmers write game code, but so do game designers and developers. Where is the line drawn? What skills do gameplay programmers use that game designers or developers do not? We're planning to upgrade an existing farm from 2007 to 2013. I learned that the best way and maybe the only way to achieve this is by migrating in two steps. 2007 to 2010 and 2010 to 2013. The actual farm is a sql-server(2008r2 64 bit) and a sperate sharepoint-server(web-frontend, etc....) I want to keep the sql-server as it is, if possible and we want to install a new 64bit host for sharepoint 2013. We will design a new branding for 2013 afterwards, so we need to keep the content, but not the layout. There's so much about migration available on the web, but Can I find something like best practises? How to differ sessions in browser-tabs? Expected area of the intersection of two circles If we pick randomly two points inside a circle centred at $O$ with radius $R$, and draw two circles centred at the two points with radius equal to the distance between them, what is the expected area of the intersection of the two cirlces that contain the origin $O$. How to add tags to files in Windows 7 so that they appear in search results In Windows 7, I want to add tags to my files (PDF, Word, Images etc) so that they appear directly in the search results, regardless of their content, title etc.    shows how to search by tag, but it does not tell how to add a tag in any file.  In the long term, I'm planning to add such tags programmatically as well. I've lost my portal home, and I am invincible. How can I leave the nether? I've gone into the Nether and seemed to have lost my portal out of it, I also can't die in lava or by mobs attacking me, I'm appear to be invincible and can't die.  This is Single Player by the way.  Why is this happening? I have a homework question that asks     Find necessary and sufficient conditions on $1 \leq i &lt; j \leq n$ so that $(i \, j)$ and $(1 \, 2 \, \dotsc \, n)$ generate $S_n$.   Here is what I have done so far.  Call $c = (1 \, 2 \, \dotsc \, n)$.  I made the observation that $$ \overbrace{c c \dotsb c}^{n - j + 1} (i \, j) \overbrace{c^{-1} c^{-1} \dotsb c^{-1}}^{n - j + 1} = (1 + i - j + n \, 1). $$ Thus, $\langle (i \, j), c \rangle = \langle (1 \, i - j + n + 1), c \rangle$, so it suffices to look at $\langle (1 \, k), c \rangle$ for positive integers $2 \leq k \leq n$.  I've checked that, for the value $k=2$, $\langle (1 \, 2), c \rangle = S_n$.  This immediately implies $\langle (1 \, n), c \rangle = S_n$.  I suspect that no other values of $k$ will work, but am not sure how to prove it. Prove that for all non-negative integers $m,n$, $\frac{(2m)!(2n)!}{m!n!(m + n)!}$ is an integer. Prove that for all non-negative integers $m,n$, $\frac{(2m)!(2n)!}{m!n!(m + n)!}$ is an integer.   I'm not familiar to factorial and I don't have much idea, can someone show me how to prove this? Thank you. How to cite own unpublished work in text and reference? How does matter know to obey physical laws? First of all, you may say that, this is a "why" question and in physics we don't ask such a question and instead we ask about "how". However, I want to discuss this with you.  We model the behavior of matter by physical laws, for example by quantum mechanics laws. I want to know how the matter, say electron, knows that it must obey such a law. What forces the electron to obey quantum mechanics laws?  If you consider a simulation of the universe in a computer, in the view of someone  simulated in that computer the physical laws are just there. They may not know what keeps  in check the simulated matter to obey physical laws, but in our perspective those simulated physical laws are there because we implemented them as zero and ones in a hard disk. If we wanted, we could change those physical laws and in the eye of the simulated person everything would be still fine.  Is there a scientific attempt to discuss this issue? so that I can read about it. When should I use "a" versus "an" in front of a word beginning with the letter h? When using an Int- or FloatProperty, is there any way of changing their min and max values dynamically?  I'm currently loading images on the fly and would like to limit a frame property to run from 0 to len(loaded_images) every time I call the loading operator. However, the property seems to be read-only and re-assigning gives the following error:  bpy.context.scene.project_props.bl_rna.properties['myIntProp'] = bpy.props.IntProperty(...) TypeError: bpy_prop_collection[key] = value: invalid, expected a StructRNA type or None, not a tuple   I understand the bpy.props constructor uses an intermediary tuple, but I'm not sure how to proceed. Is there any way around this? If $k$ is a positive integer, how to prove that there is no solution for $n$ in positive integers except $n = 1$ for $2^n = nk + 1$ Troubleshoot High CPU usage by the "System" process Is there any way to set a system wide memory limit a process can use in Windows XP? I have a couple of unstable apps which do work ok for most of the time but can hit a bug which results in eating whole memory in a matter of seconds (or at least I suppose that's it). This results in a hard reset as Windows becomes totally unresponsive and I lose my work.  I would like to be able to do something like the /etc/limits on Linux - setting M90, for instance (to set 90% max memory for a single user to allocate). So the system gets the remaining 10% no matter what. Arrow with plus/minus sign on top Below you can see an arrow with a plus and a minus sign on top of it. How is this achievable in latex? Further possibilities: arrow with only plus and arrow with only minus sign on top. How can I do this? $$ \lim \limits_{(x,y)\to (0,0)} \frac {x^2 + y^2}{\sqrt{x^2 +y^2 + 1} - 1} $$  According to my textbook the limit equals $2$.  What I have tried:  Using the squeeze theorem:  $$ \lim \limits_{(x,y)\to (0,0)} \frac {x^2 + y^2}{\sqrt{x^2 +y^2 + 1}} \le \lim\limits_{(x,y)\to (0,0)} \frac {x^2 + y^2}{\sqrt{x^2 +y^2 + 1} - 1} \le \lim\limits_{(x,y)\to (0,0)} \frac {x^2 + y^2}{\sqrt{x^2 +y^2 + 1} - 2} $$ $$ 0 \le \lim\limits_{(x,y)\to (0,0)} \frac {x^2 + y^2}{\sqrt{x^2 +y^2 + 1} - 1} \le 0 $$  I have also tried to use the squeeze theorem with two other equations and obtained different values:  $$ \lim\limits_{(x,y)\to (0,0)} \frac {x^2 + y^2 - 1}{\sqrt{x^2 +y^2 + 1}} \le \lim\limits_{(x,y)\to (0,0)} \frac {x^2 + y^2}{\sqrt{x^2 +y^2 + 1} - 1} \le \lim\limits_{(x,y)\to (0,0)} \frac {x^2 + y^2 + 1}{\sqrt{x^2 +y^2 + 1} - 2} $$ $$ -1 \le \lim\limits_{(x,y)\to (0,0)} \frac {x^2 + y^2}{\sqrt{x^2 +y^2 + 1} - 1} \le -1 $$