PIR Sensors + Arduino

A cool article from bildr regarding a PIR sensor bought at inmotion store.

Datasheet here
You can find the original article in http://bildr.org/2011/06/pir_arduino/, specially the comments which can help you a lot.

Security alarms, time lapse cameras, and those house-lights that turn on when you walk by all have something in common… Motion detection. Motion detection can be a very handy thing in installation art, interactive walls, and other times you need a cheep way to know when people are around.

PIR or Passive Infrared is a common method of motion detection that measure changes in heat to signal the change. The basic model is that they take IR (heat) images on 2 sensors at different times, when they differ, they know something has changed. This particular sensor from SparkFun beings the signal pin low when it senses a change.

Hooking it up

Hooking one up to your Arduino is pretty simple, but you need to make sure not to fall for the manufacturer’s trap. The red wire is V+ as you would think, the brown wire is ground, NOT the black wire. The black wire is the signal wire. To make matters even worse, the manufacturer uses a B/W image to show you what wire is what.

Aside from power, the signal pin connects to any digital pin on your Arduino but also needs a 10k pullup resistor between the signal and 5V.

The reason for the resistor is that the signal pin is something called an open-collector, meaning it is as if it was not connected to anything at all when nothing is signaled. When motion is sensed, it connects the pin to ground. So we use the resistor so when we read the value from that pin when no motion is detected it looks HIGH. Without the resistor the pin would be floating around and the read value would randomly float between HIGH and LOW, and we don’t want that.


The code for this is pretty simple. When it starts up, it needs 2 seconds to take an image to compare to. When we see the signal pin go low, we print some text to the serial terminal (you can replace that with any code you want) and wait 2 seconds again before checking.

You could make the code a little more sophisticated to do away with the 2sec delay after motion is sensed, but I found that the signal pin triggered on and off for a few seconds after it first sensed motion, so that delay is just to take care of that.

int pirPin = 2; //digital 2 
void setup(){ 
pinMode(pirPin, INPUT); 
void loop(){ 
int pirVal = digitalRead(pirPin); 
if(pirVal == LOW){ //was motion detected 
Serial.println("Motion Detected"); 
Unless otherwise stated, this code is released under the MIT License – Please use, change and share it.

Git cheat sheet

All the cheats for command line Git… this, or use Git Extensions @ Windows 😛
git clone <repo>

clone the repository specified by <repo>; this is similar to "checkout" in

some other version control systems such as Subversion and CVS

Add colors to your ~/.gitconfig file:


ui = auto

[color "branch"]

current = yellow reverse

local = yellow

remote = green

[color "diff"]

meta = yellow bold

frag = magenta bold

old = red bold

new = green bold

[color "status"]

added = yellow

changed = green

untracked = cyan

Highlight whitespace in diffs


ui = true

[color "diff"]

whitespace = red reverse



Add aliases to your ~/.gitconfig file:


st = status

ci = commit

br = branch

co = checkout

df = diff

dc = diff –cached

lg = log -p

lol = log –graph –decorate –pretty=oneline –abbrev-commit

lola = log –graph –decorate –pretty=oneline –abbrev-commit –all

ls = ls-files

# Show files ignored by git:

ign = ls-files -o -i –exclude-standard



git config -e [–global]

edit the .git/config [or ~/.gitconfig] file in your $EDITOR

git config –global user.name ‘John Doe’

git config –global user.email johndoe@example.com

sets your name and email for commit messages

git config branch.autosetupmerge true

tells git-branch and git-checkout to setup new branches so that git-pull(1)

will appropriately merge from that remote branch. Recommended. Without this,
you will have to add –track to your branch command or manually merge remote

tracking branches with "fetch" and then "merge".

git config core.autocrlf true

This setting tells git to convert the newlines to the system’s standard

when checking out files, and to LF newlines when committing in

git config –list

To view all options

git config apply.whitespace nowarn

To ignore whitespace

You can add "–global" after "git config" to any of these commands to make it

apply to all git repos (writes to ~/.gitconfig).



git reflog

Use this to recover from *major* mess ups! It’s basically a log of the

last few actions and you might have luck and find old commits that

have been lost by doing a complex merge.

git diff

show a diff of the changes made since your last commit

to diff one file: "git diff — <filename>"

to show a diff between staging area and HEAD: `git diff –cached`

git status

show files added to the staging area, files with changes, and untracked files

git log

show recent commits, most recent on top. Useful options:

–color with color

–graph with an ASCII-art commit graph on the left

–decorate with branch and tag names on appropriate commits

–stat with stats (files changed, insertions, and deletions)

-p with full diffs

–author=foo only by a certain author

–after="MMM DD YYYY" ex. ("Jun 20 2008") only commits after a certain date

–before="MMM DD YYYY" only commits that occur before a certain date

–merge only the commits involved in the current merge conflicts

git log <ref>..<ref>

show commits between the specified range. Useful for seeing changes from
git log HEAD..origin/master # after git remote update

git show <rev>

show the changeset (diff) of a commit specified by <rev>, which can be any

SHA1 commit ID, branch name, or tag (shows the last commit (HEAD) by default)

also to show the contents of a file at a specific revision, use

git show <rev>:<filename>

this is similar to cat-file but much simpler syntax.

git show –name-only <rev>

show only the names of the files that changed, no diff information.

git blame <file>

show who authored each line in <file>

git blame <file> <rev>

show who authored each line in <file> as of <rev> (allows blame to go back in


git gui blame

really nice GUI interface to git blame

git whatchanged <file>

show only the commits which affected <file> listing the most recent first

E.g. view all changes made to a file on a branch:

git whatchanged <branch> <file> | grep commit | \

colrm 1 7 | xargs -I % git show % <file>

this could be combined with git remote show <remote> to find all changes on

all branches to a particular file.

git diff <commit> head path/to/fubar

show the diff between a file on the current branch and potentially another

git diff –cached [<file>]

shows diff for staged (git-add’ed) files (which includes uncommitted git
cherry-pick’ed files)

git ls-files

list all files in the index and under version control.

git ls-remote <remote> [HEAD]

show the current version on the remote repo. This can be used to check whether
a local is required by comparing the local head revision.

Adding / Deleting


git add <file1> <file2> …

add <file1>, <file2>, etc… to the project

git add <dir>

add all files under directory <dir> to the project, including subdirectories

git add .

add all files under the current directory to the project

*WARNING*: including untracked files.

git rm <file1> <file2> …

remove <file1>, <file2>, etc… from the project

git rm $(git ls-files –deleted)

remove all deleted files from the project

git rm –cached <file1> <file2> …

commits absence of <file1>, <file2>, etc… from the project



Option 1:

Edit $GIT_DIR/info/exclude. See Environment Variables below for explanation on

Option 2:

Add a file .gitignore to the root of your project. This file will be checked in.

Either way you need to add patterns to exclude to these files.



git add <file1> <file2> …

git stage <file1> <file2> …

add changes in <file1>, <file2> … to the staging area (to be included in

the next commit

git add -p

git stage –patch

interactively walk through the current changes (hunks) in the working

tree, and decide which changes to add to the staging area.

git add -i

git stage –interactive

interactively add files/changes to the staging area. For a simpler

mode (no menu), try `git add –patch` (above)



git reset HEAD <file1> <file2> …

remove the specified files from the next commit



git commit <file1> <file2> … [-m <msg>]

commit <file1>, <file2>, etc…, optionally using commit message <msg>,

otherwise opening your editor to let you type a commit message

git commit -a

commit all files changed since your last commit

(does not include new (untracked) files)

git commit -v

commit verbosely, i.e. includes the diff of the contents being committed in

the commit message screen

git commit –amend

edit the commit message of the most recent commit

git commit –amend <file1> <file2> …

redo previous commit, including changes made to <file1>, <file2>, etc…



git branch

list all local branches

git branch -r

list all remote branches

git branch -a

list all local and remote branches

git branch <branch>

create a new branch named <branch>, referencing the same point in history as

the current branch

git branch <branch> <start-point>

create a new branch named <branch>, referencing <start-point>, which may be

specified any way you like, including using a branch name or a tag name

git push <repo> <start-point>:refs/heads/<branch>

create a new remote branch named <branch>, referencing <start-point> on the

remote. Repo is the name of the remote.

Example: git push origin origin:refs/heads/branch-1

Example: git push origin origin/branch-1:refs/heads/branch-2

Example: git push origin branch-1 ## shortcut

git branch –track <branch> <remote-branch>

create a tracking branch. Will push/pull changes to/from another repository.

Example: git branch –track experimental origin/experimental

git branch –set-upstream <branch> <remote-branch> (As of Git 1.7.0)

Make an existing branch track a remote branch

Example: git branch –set-upstream foo origin/foo

git branch -d <branch>

delete the branch <branch>; if the branch you are deleting points to a

commit which is not reachable from the current branch, this command

will fail with a warning.

git branch -r -d <remote-branch>

delete a remote-tracking branch.

Example: git branch -r -d wycats/master

git branch -D <branch>

even if the branch points to a commit not reachable from the current branch,

you may know that that commit is still reachable from some other branch or

tag. In that case it is safe to use this command to force git to delete the


git checkout <branch>

make the current branch <branch>, updating the working directory to reflect

the version referenced by <branch>

git checkout -b <new> <start-point>

create a new branch <new> referencing <start-point>, and check it out.

git push <repository> :<branch>

removes a branch from a remote repository.

Example: git push origin :old_branch_to_be_deleted

git co <branch> <path to new file>

Checkout a file from another branch and add it to this branch. File

will still need to be added to the git branch, but it’s present.

Eg. git co remote_at_origin__tick702_antifraud_blocking

git show <branch> — <path to file that does not exist>

Eg. git show remote_tick702 — path/to/fubar.txt

show the contents of a file that was created on another branch and that

does not exist on the current branch.

git show <rev>:<repo path to file>

Show the contents of a file at the specific revision. Note: path has to be

absolute within the repo.



git merge <branch>

merge branch <branch> into the current branch; this command is idempotent

and can be run as many times as needed to keep the current branch

up-to-date with changes in <branch>

git merge <branch> –no-commit

merge branch <branch> into the current branch, but do not autocommit the

result; allows you to make further tweaks

git merge <branch> -s ours

merge branch <branch> into the current branch, but drops any changes in

<branch>, using the current tree as the new tree



git cherry-pick [–edit] [-n] [-m parent-number] [-s] [-x] <commit>

selectively merge a single commit from another local branch

Example: git cherry-pick 7300a6130d9447e18a931e898b64eefedea19544

git hash-object <file-path>

get the blob of some file whether it is in a repository or not

Find the commit in the repository that contains the file blob:


git log –pretty=format:’%T %h %s’ \

| while read tree commit subject ; do

if git ls-tree -r $tree | grep -q "$obj_blob" ; then

echo $commit "$subject"





WARNING: "git rebase" changes history. Be careful. Google it.

git rebase –interactive HEAD~10

(then change all but the first "pick" to "squash")

squash the last 10 commits into one big commit



git mergetool

work through conflicted files by opening them in your mergetool (opendiff,

kdiff3, etc.) and choosing left/right chunks. The merged result is staged for


For binary files or if mergetool won’t do, resolve the conflict(s) manually

and then do:

git add <file1> [<file2> …]

Once all conflicts are resolved and staged, commit the pending merge with:

git commit



git fetch <remote>

update the remote-tracking branches for <remote> (defaults to "origin").

Does not initiate a merge into the current branch (see "git pull" below).

git pull

fetch changes from the server, and merge them into the current branch.

Note: .git/config must have a [branch "some_name"] section for the current

branch, to know which remote-tracking branch to merge into the current

branch. Git 1.5.3 and above adds this automatically.

git push

update the server with your commits across all branches that are *COMMON*

between your local copy and the server. Local branches that were never

pushed to the server in the first place are not shared.

git push origin <branch>

update the server with your commits made to <branch> since your last push.

This is always *required* for new branches that you wish to share. After

the first explicit push, "git push" by itself is sufficient.

git push origin <branch>:refs/heads/<branch>

E.g. git push origin twitter-experiment:refs/heads/twitter-experiment

Which, in fact, is the same as git push origin <branch> but a little

more obvious what is happening.



git revert <rev>

reverse commit specified by <rev> and commit the result. This does *not* do

the same thing as similarly named commands in other VCS’s such as "svn

revert" or "bzr revert", see below

git checkout <file>

re-checkout <file>, overwriting any local changes

git checkout .

re-checkout all files, overwriting any local changes. This is most similar

to "svn revert" if you’re used to Subversion commands

Fix mistakes / Undo


git reset –hard

abandon everything since your last commit; this command can be DANGEROUS.

If merging has resulted in conflicts and you’d like to just forget about

the merge, this command will do that.

git reset –hard ORIG_HEAD or git reset –hard origin/master

undo your most recent *successful* merge *and* any changes that occurred

after. Useful for forgetting about the merge you just did. If there are

conflicts (the merge was not successful), use "git reset –hard" (above)


git reset –soft HEAD^

forgot something in your last commit? That’s easy to fix. Undo your last

commit, but keep the changes in the staging area for editing.

git commit –amend

redo previous commit, including changes you’ve staged in the meantime.

Also used to edit commit message of previous commit.



test <sha1-A> = $(git merge-base <sha1-A> <sha1-B>)

determine if merging sha1-B into sha1-A is achievable as a fast forward;

non-zero exit status is false.



git stash

git stash save <optional-name>

save your local modifications to a new stash (so you can for example

"git svn rebase" or "git pull")

git stash apply

restore the changes recorded in the stash on top of the current working tree


git stash pop

restore the changes from the most recent stash, and remove it from the stack

of stashed changes

git stash list

list all current stashes

git stash show <stash-name> -p

show the contents of a stash – accepts all diff args

git stash drop [<stash-name>]

delete the stash

git stash clear

delete all current stashes



git remote add <remote> <remote_URL>

adds a remote repository to your git config. Can be then fetched locally.


git remote add coreteam git://github.com/wycats/merb-plugins.git

git fetch coreteam

git push <remote> :refs/heads/<branch>

delete a branch in a remote repository

git push <remote> <remote>:refs/heads/<remote_branch>

create a branch on a remote repository

Example: git push origin origin:refs/heads/new_feature_name

git push <repository> +<remote>:<new_remote>

replace a <remote> branch with <new_remote>

think twice before do this

Example: git push origin +master:my_branch

git remote prune <remote>

prune deleted remote-tracking branches from "git branch -r" listing

git remote add -t master -m master origin git://example.com/git.git/

add a remote and track its master

git remote show <remote>

show information about the remote server.

git checkout -b <local branch> <remote>/<remote branch>


git checkout -b myfeature origin/myfeature

git checkout -b myfeature remotes/<remote>/<branch>

Track a remote branch as a local branch. It seems that

somtimes an extra ‘remotes/’ is required, to see the exact

branch name, ‘git branch -a’.

git pull <remote> <branch>

git push

For branches that are remotely tracked (via git push) but

that complain about non-fast forward commits when doing a

git push. The pull synchronizes local and remote, and if

all goes well, the result is pushable.

git fetch <remote>

Retrieves all branches from the remote repository. After

this ‘git branch –track …’ can be used to track a branch

from the new remote.



git submodule add <remote_repository> <path/to/submodule>

add the given repository at the given path. The addition will be part of the

next commit.

git submodule update [–init]

Update the registered submodules (clone missing submodules, and checkout

the commit specified by the super-repo). –init is needed the first time.

git submodule foreach <command>

Executes the given command within each checked out submodule.

Removing submodules

1. Delete the relevant line from the .gitmodules file.

2. Delete the relevant section from .git/config.

3. Run git rm –cached path_to_submodule (no trailing slash).

4. Commit and delete the now untracked submodule files.

Updating submodules

To update a submodule to a new commit:

1. update submodule:

cd <path to submodule>

git pull

2. commit the new version of submodule:

cd <path to toplevel>

git commit -m "update submodule version"

3. check that the submodule has the correct version

git submodule status

If the update in the submodule is not committed in the

main repository, it is lost and doing git submodule

update will revert to the previous version.



git format-patch HEAD^

Generate the last commit as a patch that can be applied on another

clone (or branch) using ‘git am’. Format patch can also generate a

patch for all commits using ‘git format-patch HEAD^ HEAD’

All page files will be enumerated with a prefix, e.g. 0001 is the

first patch.

git format-patch <Revision>^..<Revision>

Generate a patch for a single commit. E.g.

git format-patch d8efce43099^..d8efce43099

Revision does not need to be fully specified.

git am <patch file>

Applies the patch file generated by format-patch.

git diff –no-prefix > patchfile

Generates a patch file that can be applied using patch:

patch -p0 < patchfile

Useful for sharing changes without generating a git commit.



git tag -l

Will list all tags defined in the repository.

git co <tag_name>

Will checkout the code for a particular tag. After this you’ll

probably want to do: ‘git co -b <some branch name>’ to define

a branch. Any changes you now make can be committed to that

branch and later merged.



git archive master | tar -x -C /somewhere/else

Will export expanded tree as tar archive at given path

git archive master | bzip2 > source-tree.tar.bz2

Will export archive as bz2

git archive –format zip –output /full/path master

Will export as zip

Git Instaweb


git instaweb –httpd=webrick [–start | –stop | –restart]

Environment Variables



Your full name to be recorded in any newly created commits. Overrides

user.name in .git/config


Your email address to be recorded in any newly created commits. Overrides

user.email in .git/config


Location of the repository to use (for out of working directory repositories)


Location of the Working Directory – use with GIT_DIR to specifiy the working
directory root
or to work without being in the working directory at all.

Changing history


Change author for all commits with given name

git filter-branch –commit-filter ‘

if [ "$GIT_COMMITTER_NAME" = "<Old Name>" ];






git commit-tree "$@";


git commit-tree "$@";

fi’ HEAD

Raspberry Pi hangs

So… after solved the last hangups, so more things changed by this side.

My new raspberry pi had arrived, and it was time do turn the one that i’ve been trying to Vasco.

So, took the sdcard from one, and plugged in another. Only have to change the internet stuff at router. At this time i’ve taked the usb cable from my samsung phone and replaced with a cheap one bought in ebay.

So, after that hangs came back….

Our software being developed had changed too.

After reading some stuff, I’ve decided to replace the usb cable with the previous. This hangs are different than the other in the past. Last one there was messages in the stdout about kernel panics… in this don’t.

In the beginning the overload was a thing that i blamed, but after being working in the pi and it blocked without anything special running… made me think. So replacing the cable with the samsung one helped a lot.

Still some hangs persist, not regular.

So ‘ive decided. I will change to raspberry pi debian wheezy beta.

Still, it may solve some things, but there is a unsure rumour about a pl2303 interface being causing problems.

I’ve being using one in our projects to parse the XML supplied by a Current Cost Envi. So despite the huge load caused by python, the arduino usb  interface being bug fixed to interface better with the home X10 interface, some lockups in the sqlite database used by python and web interface, and this new fact of the pl2303 i’m not quite sure of what’s the real problem.

Since the device don’t have anything on the screen when it crashes it’s complicated. My best bet is now the pl2303, which seen in a forum that can be solved with deleting the module and inserting it again with some tweaks.

But let’s try wheezy. It should be better for sure.