Extract page from pdf and convert to png

Extreure la pàgina que volem:
$ pdftk Caminant.pdf cat 1 output p1.pdf

Convertir-ho al que convingui, aquí en jpg
$ convert -units PixelsPerInch -density 300 p1.pdf p1_300.jpg

Si volem extreure totes les pàgines:
$ pdftk Caminant.pdf burst
Això ens crea un fitxer pg_xxxx.pdf per cada pàgina i un fitxer resum del que hi havia al pdf original
Ara, per convertir totes les pàgines de cop, podem fer:
for file in pg_*.pdf ; do convert -units PixelsPerInch -density 300 "$file" "${file%.*}.jpg" ; done 

Combinació de pdftk i de convert en una línia:

$ pdftk A=filein.pdf cat A14  output - | convert -density 96 - fileout.png

Els guions substitueixen els noms que hi hauria:

• A pdftk faríem ... output output.pdf.
• A convert faríem convert ... filein.pdf fileout.png

I ara per extreure-ho i convertir-ho en un nou PDF, per si el PDF original té problemes de fonts o qualsevol altre problema.
Aquí es fa a 96 dpi, però es pot fer a més resolució, si interessa.

$ pdftk A=POG.pdf cat A14  output - | convert -density 96 - - | convert - pag14.pdf

Això es pot fer automatitzat

NPAGES=$(pdfinfo $1 | grep Pages | awk '{print $2}')

echo $NPAGES

for i in $(seq $NPAGES); do
  echo Processing page $i
  echo Generating "FILE$i".png
  pdftk  A=$1 cat "A$i" output - | convert -density 96 - "__FILE$i".png
done

Octave: Fit Gaussian to data

% Adjust a gaussian
% Define the gaussian function
gausFun = @(hms,x) hms(1) .* exp (-(x-hms(2)).^2 ./ (2*hms(3)^2)) ;
init=[100;0;20]; % Hmax, mean, sigma
[P, FY, CVG, OUTP] = nonlin_curvefit (gausFun , init', XX, NN);
%Print estimated sigma
sigma_est=P(3)

Raspberry pi zero W

Enable headless operation

1. Download raspbian and write to micro-SD card
2. Mount on PC and, on the boot partition:
3. Create an (empty) file called ssh (this enable SSH on startup)
4. Create a wpa_supplicant.conf file with the following content

network={
    ssid="YOUR_WIFI_SSID"
    psk="YOUR_WIFI_PASSWORD"
    key_mgmt=WPA-PSK
}

 

On Off button

Poweroff

To poweroff, follow these instructions:

Essentially:
Connect button between GPIO18 and GND
Write this python script

1. 
   

   1. #!/bin/python  
   2. # Simple script for shutting down the raspberry Pi at the press of a button.  
   3. # by Inderpreet Singh  
   4.   
   5. import RPi.GPIO as GPIO  
   6. import time  
   7. import os  
   8.  
   9. # Use the Broadcom SOC Pin numbers  
   10. # Setup the Pin with Internal pullups enabled and PIN in reading mode.  
   11. GPIO.setmode(GPIO.BCM)  
   12. GPIO.setup(18, GPIO.IN, pull_up_down = GPIO.PUD_UP)  
   13.  
   14. # Our function on what to do when the button is pressed  
   15. def Shutdown(channel):  
   16.     os.system("sudo shutdown -h now")  
   17.  
   18. # Add our function to execute when the button pressed event happens  
   19. GPIO.add_event_detect(18, GPIO.FALLING, callback = Shutdown, bouncetime = 2000)  
   20.  
   21. # Now wait!  
   22. while 1:  
   23.     time.sleep(1)  
   
   
   
   
   

We need our python script to run automatically every time the RPi starts. For this we need to do a little manual editing of the RPI generated files. Run the following command

1. sudo nano /etc/rc.local 

This file is what gets executed everytime your RPi boots up. We need to add our python command before the last line which closes the if loop. Therefore, add the following line before the #fi at the end of the file.

1. sudo python /home/pi/Scripts/shutdown_pi.py & 

Please note that everything is case sensitive so Scripts is not the same as scripts. The & at the end of the command tells it to run the process in the background. If you omit it, then your login prompt probably will not appear.

Poweron

To poweron, place a button across the RUN header of the RPI zero. This is actually a reset button but when halted can bring the Pi on again.

Power Consumption

During boot, I have seen peaks of 240 mA.
After shutdown, power consumption is 30 mA.

SPICE with Python

PySpice seems to be a great tool!
Just do
git clone https://github.com/FabriceSalvaire/PySpice
and install everything that it needs:
PySpice requires the following dependencies:

• Python 3
• Numpy
• Matplotlib
• Ngspice
• CFFI (only required for Ngspice shared)

The way to organize a project is to have the file.py, a folder called libraries and inside put folders with the element.lib files. These can also be put into folders to easily organize things. Then, call this

libraries_path = os.path.join(os.path.dirname(os.path.dirname(__file__)), 'libraries')
spice_library = SpiceLibrary(libraries_path)
circuit.include(spice_library['2n2222a'])
circuit.BJT(1, 'collector', 'base', circuit.gnd, '2n2222a')

Resistor
circuit.R( name, +node, -node, value) 
circuit.R(1, 'out', circuit.gnd, kilo(5))

Capacitor
circuit.C(1, +node, -node, value)
circuit.C(1, +node, -node, value, initial_condition=5)

BJT
circuit.BJT(1, 'collector', 'base', circuit.gnd, '2n2222a')


Results
analysis.base : the voltage of node named 'base'





Interesting features
https://github.com/FabriceSalvaire/PySpice/blob/gh-pages/downloads/voltage-divider.py
Shows how to put a voltage source defined in Python into Spice. This probably means that you can have an arbitrary function generator in Python!!!

Coses sobre l'esquena i els isquiotibials

https://breakingmuscle.com/learn/2-overlooked-reasons-your-hamstrings-are-tight

https://breakingmuscle.com/learn/cant-touch-your-toes-find-and-fix-the-root-of-the-problem

https://breakingmuscle.com/learn/are-your-weak-neck-muscles-making-your-hamstrings-tight

Arduino. On és el main?

Exactament què fa un programa en Arduino?

Executa un loop com aquest: https://github.com/arduino/Arduino/blob/master/hardware/arduino/avr/cores/arduino/main.cpp

int main(void) {
    init();
    initVariant();
   
    setup();
   
    for (;;) {
        loop();
        if (serialEventRun) serialEventRun();
    }  
    return 0;
}

Executa una vegada el setup de client i crida repetidament loop() més serialEventRun.

Tot el codi principal està aquí https://github.com/arduino/Arduino/tree/master/hardware/arduino/avr/cores/arduino

Un element important és Arduino.h (en les versions "modernes" de Arduino).

Flight Controller

One of the best tutorials I have found on flight controllers

http://blog.owenson.me/build-your-own-quadcopter-flight-controller/

Python debugging

Install interactive debugging

sudo -H pip install ipdb

To debug a script in ipython
that uses parameters in its call:

ipython -m ipdb './xvalues.py' -- -d TUB

The parameters for the script are passed after "--"

Once you have the shell, the useful commands are:

• n "next"
• <ENTER> repeats the last command
• p "print" p variable
• s "step into"
• b "breakpoint" b. This can be interesting: break at line 25: b 25. Break when method x of object y is called b y.x
• r "continue to end of subroutine"
• c "continue till the end"

Useful link
https://pythonconquerstheuniverse.wordpress.com/2009/09/10/debugging-in-python/

What to do if Ubuntu freezes?

https://askubuntu.com/questions/4408/what-should-i-do-when-ubuntu-freezes