Tag Archives: Pi

Raspberry Pi Thermal Probe

How to read a temperature probe, save the value to a MySQL database and then show the value on a webpage or just show the value with no database.

 

See this link for how to setup a DS18B20+ thermal probe with a Raspberry Pi, these instructions  are the best that i have come across for this and will cover the bullet points below :

  • Enabling the 1 wire features in the Raspbian OS
  • Physically connecting the probe via a resistor to the RPi
  • Instructions on how to read the probe and a script example

https://www.modmypi.com/blog/ds18b20-one-wire-digital-temperature-sensor-and-the-raspberry-pi

Once you have followed the above steps you should have a working temperature probe, that’s great.. but what can you do with it now!?

For the piTank/piGrow projects,  I started off by just using the script provide in the instructions above, modifying it slightly and using that to display the temperature value on the piTank web-page. Using some JavaScript you can make the box’s refresh every x seconds, running the probe read script and showing a new value without the need for a page reload.  I call this a ‘live’ reading.

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Raspberry Pi Slideshow .PPT .PPTX .ODP

The information below will help you to setup a Raspberry Pi with Raspbian OS that will play a slideshow/PowerPoint presentation using a PPT/PPTX or ODP file.

The system will be setup to automatically login to a desktop, load Libre Office Impress (PowerPoint alternative) and run a slide show presentation with custom slide show settings defined.

Please note, MS Powerpoint slideshows might not display 100% correctly in Libre, you can save from MS PP to an open format or to ensure an output as expected, just grab Libre office for PC or Mac, it is Free after all!!

Why:

Instead of using a costly full blown MS Windows desktop PC we can use a Raspberry Pi that not only costs hundreds of pounds less to buy but also consumes a minor percentage of power that a full desktop uses as well as being small enough to attach to the rear of the display device.

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Raspberry Pi Enable Cron

By default,  Cron is disabled meaning anything entered into  ‘crontab’ wont be run.

To enable this function, follow the steps below:

Once logged into the Pi use the below command to open up the ‘rsyslog.conf’ file in the Nano editor

cd/etc
sudo nano rsyslog.conf

Once the rsyslog is loaded into nano, navigate to the below section and un-comment the ‘cron’ option

#
# First some standard log files.  Log by facility.
#
auth,authpriv.*              /var/log/auth.log
*.*;auth,authpriv.none          -/var/log/syslog
cron.*                          /var/log/cron.log
daemon.*                        -/var/log/daemon.log
kern.*                          -/var/log/kern.log
lpr.*                           -/var/log/lpr.log
mail.*                          -/var/log/mail.log
user.*                          -/var/log/user.log

Save the document by pressing CTRL + O and then CTRL+X  close the editor.

Reboot the Raspberry Pi:

sudo reboot

Raspberry Pi GPIO Start-up Script

On powering/reset of the Raspberry Pi connected to a relay board, the state of the relays needs to be defined or they just sit in limbo until their first use, this might be fine in some application but not others..

For my Raspberry Pi  aquarium system, the ‘original‘ Web UI does have a script on loading the webpage to define the pin modes but if there is a power cut and the RPi is restarted, we need these values set and activated when the RPi boots in case nobody loads the piTank webpage directly after a reboot – thus critical components wont be turned on.

The fix to this issue is gpiobootscript.sh

GPIO Readall

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