Know How... 194: Raspberry Pi Day!

Build your own Raspberry Pi Security Cam, how to install the official Raspberry Pi 7" touchscreen, and learn the math for how much battery you'll need to power your next project.

Build Your Own Security Camera

Parts Needed:

• Raspberry Pi Model B Revision 2.0 (512MB)
• Micro SD card 8GB or higher
• Webcam Logitech HD Webcam C520
• Usb with external Power Supply

Setting up RaspPi

• Prepare / Format your SD Card
• Download Raspbian Jessie Lite
• Download WinDisk Imager (Or image writer for your OS)
• Insert Card and Boot up Pi
• Find your IP - ifconfig
• Enable SSH - sudo raspi-config
• Set Up Motion - sudo apt-get update - sudo apt-get upgrade
• Install Motion - sudo apt-get install motion
• Check if Raspberry Pi sees webcam - lsusb
• You should see the webcam pop up on the list of USB devices
• Now to Configure Motion - sudo nano /etc/motion/motion.conf
• In case you're using a RasPi 1 or want to make sure you can get your camera working properly; - output_pictures off - ffmpeg_output_movies off - stream_maxrate 30 - stream_localhost off "ctrl x" to save.
• Set Motion to begin at startup - sudo nano /etc/default/motion - start_motion_daemon=yes
• Start and Stop Motion - sudo service motion start - sudo service motion stop
• Done!!!

How long will my battery last?

"I'm trying to figure out the battery life for my lighting project, and I'm hoping you guys can help me out... I have a Lohas 100 watt LED chip, which is being powered by a 5200 mAh 30C lipo. I used an LM2577 power converter to get from ~12v to 35v. While simply knowing the answer would be nice, I'd really like to know how the math works, so I can do it myself in the future." -- 52Degrees

Watt: Unit of Energy per time
Volt: Unit of Electrical Potential
Amp: Unit of Electrical Current

• If you were to think of Volts and Amps in terms of a wave, how high a wave is would be the voltage, and how BIG, or how much water was IN the wave would be the Amperage
• Together, how HIGH and how BIG the wave is determines how much ENERGY the wave can impart over time.

Let's use my favorite equation: "West Virgina" or "Watts = volts x amps"

This is a FANTASTIC relationship for us engineers, because it means we can play with voltage and current to get the amount of wattage that we need for an application

Example:

• Let's take a 100 watt bulb
  • I need 100 energy units (watts) over the course of an hour (Watt/Hour) to keep it lit.
• Assuming that the bulb can handle a variable range of voltage and current, there are several ways I can supply that power:
  1. I can provide high voltage and low current (i.e. 100 volts & 1 amp)
  2. I can provide low voltage and high current (i.e. 1 volt & 100 amps)
  3. I can provide something in between (i.e. 10 volts & 10 amps)
• All of these scenarios will give me 100 units of power (watt) over the course of an hour (watt-hour)

Ok... now to HIS question:

• He was a 100Watt/Hour LED
• He has 5300mAh 3S 30C battery

So Let's do the Math!

1. The Battery has 5300mAh of CAPACITY at 11.1 volts (12volts)
2. If we multiply 5.3Ah (that's 5300mAh) by 11.1 volts, we get 58.83Watt/Hours of capacity.
   • This means if we were to pull 58.83 watts of power, the battery would be COMPLETELY drained in an hour.
3. HOWEVER, LiPo batteries have a "discharge rating" (in his case, 30C)
   • This determines the MAX current at which you can pull power from the pack.
   • 30c X

Let

These show notes have been truncated due to length. For the full show notes, visit https://twit.tv/shows/know-how/episodes/194

Hosts: Fr. Robert Ballecer, SJ and Bryan Burnett

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