By Dave Thomas, David Heinemeier Hansson, Sam Ruby
Ruby on Rails is helping you produce top quality, beautiful-looking internet functions fast. you consider developing the applying, and Rails looks after the details.
Tens of millions of builders have used this award-winning e-book to benefit Rails. It's a wide, far-reaching instructional and reference that's advised via the Rails middle group. If you're new to Rails, you'll get step by step suggestions. If you're an skilled developer, this ebook provide you with the excellent, insider info you need.
Rails has advanced through the years, and this e-book has developed besides it. We nonetheless commence with a step by step walkthrough of creating a true program, and in-depth chapters examine the integrated Rails beneficial properties. This version now offers new Ruby and Rails clients additional information at the Ruby language and takes extra time to provide an explanation for key ideas all through. most sensible practices on the right way to practice Rails proceed to alter, and this version retains up. Examples use cookie subsidized periods, HTTP authentication, and energetic Record-based types, and the e-book focuses all through at the correct option to use Rails. also, this version now displays Ruby 1.9, a brand new liberate of Ruby with huge useful and function improvements.
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Extra resources for Agile Web Development with Rails (4th edition)
The power equation is as follows: P = IV Where P is power in watts, and I and V are still defined as the current and voltage. 02A = 60mW, well under the resistor’s rating of 1/8W, or 125mW. So, you do not have to worry about the resistor overheating; it is well within its operating limits. Programming Digital Outputs By default, all Arduino pins are set to inputs. If you want to make a pin an output, you need to first tell the Arduino how the pin should be configured. In the Arduino programming language, the program requires two parts: the setup() and the loop().
Of course, because this is all in the main loop, this pattern repeats ad infinitum. Be sure to note a few differences in this for loop. In the first loop, i++ is just shorthand code to represent i=i+1. Similarly, i-- is functionally equivalent to i=i–1. The first for loop fades the LED up, and the second loop fades it down. PWM control can be used in lots of circumstances to emulate pure analog control, but it cannot always be used when you actually need an analog signal. For instance, PWM is great for driving direct current (DC) motors at variable speeds (you experiment with this in later chapters), but it does not work well for driving speakers unless you supplement it with some external circuitry.
Knowing that you want approximately 20mA to flow through these components, you can find the resistor value by solving for R: R = V/I Where V = 3V and I = 20mA. 02A = 150Ω. So, with a resistor value of 150Ω, 20mA flows through both the resistor and LED. As you increase the resistance value, less current is allowed to flow through. 220Ω is a bit more than 150Ω, but still allows the LED to glow sufficiently bright, and is a very commonly available resistor value. Another useful equation to keep in mind is the power equation.