Il faut créer une variable pour contrôler l’affichage LCD:
| Retourne: | objet |
|---|---|
| Type retourné: | Adafruit_CharLCDPlate() |
Ici la variable créée est lcd
Avec Firmata sur l’Arduino. Comme avec l’écran, Création de la variable :
| Paramètres: | id (string) – identifiant de l’Arduino dans le répertoire /dev |
|---|---|
| Retourne: | objet Arduino |
| Type retourné: | Arduino |
Ici, la variable est appelée board.
Il faut ensuite commencer l’écoute sur les entrées :
| Paramètres: | i (integer) – numéro de l’entrée analogique |
|---|---|
| Retourne: | None |
Lorsque la Raspberry Pi commence à écouter, l’Arduino renvoit comme valeur None au début, il faut donc attendre que l’Arduino envoit une valeur valide avant de commencer.
On désire avoir un fichier par capteur et un fichier d’horodatage. La création des fichiers se fait en 3 étapes :
- définition du répertoire de stockage des fichiers
- création des fichiers et d’une liste
- ouverture des fichiers et remplissage de la liste
La liste permet de stocker le nom des fichiers.
Pour toutes ces opérations, on utilisera le module os.
On lit dans quel dossier on se trouve actuellement avec
getcwd() -> path
Return a unicode string representing the current working directory.
Puis on définit le dossier de sortie par la chaîne de caractères “data” et on crée le chemin avec
Join two or more pathname components, inserting ‘/’ as needed. If any component is an absolute path, all previous path components will be discarded. An empty last part will result in a path that ends with a separator.
| Paramètres: |
|
|---|---|
| Retourne: | nouveau chemin |
| Type retourné: | string |
On obtient alors le chemin du dossier dans lequel seront stockés les fichiers
Si le dossier n’existait pas, il est créé avec
makedirs(path [, mode=0o777][, exist_ok=False])
Super-mkdir; create a leaf directory and all intermediate ones. Works like mkdir, except that any intermediate path segment (not just the rightmost) will be created if it does not exist. If the target directory with the same mode as we specified already exists, raises an OSError if exist_ok is False, otherwise no exception is raised. This is recursive.
| Paramètres: | newpath – chemin du dossier à créer |
|---|---|
| Retourne: | None |
L’existence du dossier est testée avec :
Test whether a path exists. Returns False for broken symbolic links
| Paramètres: | newpath (string) – chemin dont on regarde l’existence |
|---|---|
| Retourne: | booléen indiquant l’existence ou non du dossier |
| Type retourné: | boolean |
On crée la liste contenant les fichiers nommée fileList. On crée les noms de fichiers :
| Paramètres: | i (integer) – numéro de l’entrée analogique correspondant à ce fichier |
|---|---|
| Retourne: | le nom de fichier sous la forme data_i avec i le numéro d’entrée analogique |
| Type retourné: | string |
On crée le chemin du fichier avec
| Retourne: | le chemin complet du fichier |
|---|
Enfin, on ouvre le fichier avec
Open file and return a stream. Raise IOError upon failure.
file is either a text or byte string giving the name (and the path if the file isn’t in the current working directory) of the file to be opened or an integer file descriptor of the file to be wrapped. (If a file descriptor is given, it is closed when the returned I/O object is closed, unless closefd is set to False.)
mode is an optional string that specifies the mode in which the file is opened. It defaults to ‘r’ which means open for reading in text mode. Other common values are ‘w’ for writing (truncating the file if it already exists), ‘x’ for creating and writing to a new file, and ‘a’ for appending (which on some Unix systems, means that all writes append to the end of the file regardless of the current seek position). In text mode, if encoding is not specified the encoding used is platform dependent: locale.getpreferredencoding(False) is called to get the current locale encoding. (For reading and writing raw bytes use binary mode and leave encoding unspecified.) The available modes are:
| Character | Meaning |
| ‘r’ | open for reading (default) |
| ‘w’ | open for writing, truncating the file first |
| ‘x’ | create a new file and open it for writing |
| ‘a’ | open for writing, appending to the end of the file if it exists |
| ‘b’ | binary mode |
| ‘t’ | text mode (default) |
| ‘+’ | open a disk file for updating (reading and writing) |
| ‘U’ | universal newline mode (deprecated) |
The default mode is ‘rt’ (open for reading text). For binary random access, the mode ‘w+b’ opens and truncates the file to 0 bytes, while ‘r+b’ opens the file without truncation. The ‘x’ mode implies ‘w’ and raises an FileExistsError if the file already exists.
Python distinguishes between files opened in binary and text modes, even when the underlying operating system doesn’t. Files opened in binary mode (appending ‘b’ to the mode argument) return contents as bytes objects without any decoding. In text mode (the default, or when ‘t’ is appended to the mode argument), the contents of the file are returned as strings, the bytes having been first decoded using a platform-dependent encoding or using the specified encoding if given.
‘U’ mode is deprecated and will raise an exception in future versions of Python. It has no effect in Python 3. Use newline to control universal newlines mode.
buffering is an optional integer used to set the buffering policy. Pass 0 to switch buffering off (only allowed in binary mode), 1 to select line buffering (only usable in text mode), and an integer > 1 to indicate the size of a fixed-size chunk buffer. When no buffering argument is given, the default buffering policy works as follows:
encoding is the name of the encoding used to decode or encode the file. This should only be used in text mode. The default encoding is platform dependent, but any encoding supported by Python can be passed. See the codecs module for the list of supported encodings.
errors is an optional string that specifies how encoding errors are to be handled—this argument should not be used in binary mode. Pass ‘strict’ to raise a ValueError exception if there is an encoding error (the default of None has the same effect), or pass ‘ignore’ to ignore errors. (Note that ignoring encoding errors can lead to data loss.) See the documentation for codecs.register or run ‘help(codecs.Codec)’ for a list of the permitted encoding error strings.
newline controls how universal newlines works (it only applies to text mode). It can be None, ‘’, ‘n’, ‘r’, and ‘rn’. It works as follows:
If closefd is False, the underlying file descriptor will be kept open when the file is closed. This does not work when a file name is given and must be True in that case.
A custom opener can be used by passing a callable as opener. The underlying file descriptor for the file object is then obtained by calling opener with (file, flags). opener must return an open file descriptor (passing os.open as opener results in functionality similar to passing None).
open() returns a file object whose type depends on the mode, and through which the standard file operations such as reading and writing are performed. When open() is used to open a file in a text mode (‘w’, ‘r’, ‘wt’, ‘rt’, etc.), it returns a TextIOWrapper. When used to open a file in a binary mode, the returned class varies: in read binary mode, it returns a BufferedReader; in write binary and append binary modes, it returns a BufferedWriter, and in read/write mode, it returns a BufferedRandom.
It is also possible to use a string or bytearray as a file for both reading and writing. For strings StringIO can be used like a file opened in a text mode, and for bytes a BytesIO can be used like a file opened in a binary mode.
On procède de même avec le fichier d’horodatage, sauf que le nom ne sera pas data_i mais timestamp.
L’initialisation de l’horodatage est faite dans la boucle principale pour avoir le moins d’écart entre l’initialisation du temps et la première mesure, i.e pour que la première mesure ait pour abscisse 0.
Pour cela on crée un booléen timestampInitDone qu’on met à False au début. On va donc faire l’initialisation du timestamp si et seulement si timestampInitDone est à False :
#### CREATION DU TIMESTAMP ####
On utilise la fonction time.time pour initialiser l’horodatage :
time() -> floating point number
Return the current time in seconds since the Epoch. Fractions of a second may be present if the system clock provides them.
On met ensuite le booléen timestampInitDone à True pour indiquer que l’initialisation de l’horodatage a été effectuée.