4 ms·

Do you have a layman's explanation for what the 555 timer is used for and how it works?

• colejohnson66 5y ago
  It's such a simple IC that it's hard to see what it can do. But if you stick some resistors and capacitors around it in just the right ways, it can do so much. Google "555 examples" for thousands of example schematics. Wikipedia has a few examples: https://en.wikipedia.org/wiki/555_timer_IC#Modes https://en.wikipedia.org/wiki/555_timer_IC#Modes
• deleted 5y ago
  [deleted]
• kens 5y ago
  The basic idea of the 555 timer is to generate a pulse of a fixed timing, from microseconds to hours. But it is a very flexible chip so it has hundreds of applications, operating as anything from a timer or latch to a voltage-controlled oscillator or modulator. As a result, the chip was very widely used. How it works is that when you charge a capacitor through a resistor, the capacitor will charge relatively slowly. The rate depends on the value of the components. What the 555 chip does is monitors the voltage level on the capacitor. When it reaches an upper level, the chip discharges the capacitor. When the voltage reaches a lower level, the chip starts charging the capacitor. Thus you get oscillations with the desired timing. Think of it kind of like filling your sink with water. When the sink gets 2/3 full, you pull the plug from the drain. When the water level drops to 1/3, you put the plug back in the drain. This will give you periodic oscillations. The timing depends on the size of the sink (capacitor) and how much you open the tap (resistor).
  • tadbit 5y ago
    This is a fantastic explanation. Thank you!
  • altcognito 5y ago
    How do you get such a wide range of times with such a tiny capacitor? I imagine there is some magic with multiplying this effect across multiple caps?
    • kens 5y ago
      For a short delay, you use a small resistor and a small capacitor. For a long delay, you use a large resistor and a large capacitor. The result is that it supports "timing from microseconds through hours." The timing resistors and capacitors are external, so you can select whatever values you want for your application.
    • bonzini 5y ago
      It's not necessarily tiny. You could use an electrolytic capacitor with a capacity of a few millifarads, for example. However, the tolerance of larger capacitors is larger (usually 20%, and up to 50%) so that quickly becomes expensive. It's more likely that you'll generate a 10 second or less pulse with the 555 and then make it longer using (for example) T flip-flops. A single 744040 ripple counter IC for example can divide the output by up to 4096.