The IC555 part 2

Hello, we return today to continue talking about the IC555, this post will shown and explained how the 555 will be used to turn the LCD backlight.

I found the montage that we will use in an old electronics magazine, this setup is simpler than those found on the Internet, but works with great precision.

Seen by the image we will use three resistors, a capacitor and a button (could be four resistors, but there’s no need).
The calculation for the time that the circuit is enabled follows this formula:

In the example we have RT = 546 and CT = 100.

The units will be T [s], CT [µF], RT [KΩ]. We think 5s is sufficient to look at the LCD, then remains to use a value to a variable, and find the other.
We decided to use CT = 100 [µF], then making a calculation using the equation we obtain RT = 45,45 [KΩ].

The commercial value that 45,45 is closer is the 47. Then redoing the calculations for 47 [KΩ] and 100 [µF], we obtain T = 5.17 [s], an accuracy more than enough for our project.

In the next post will show how the 555 will be connected to the LCD.
By!