The 555 timer IC has been used in electronics projects for decades.
The 555 timer integrated circuit (IC), first introduced in the 1970s, is a perennial favorite among electronics designers and hobbyists. Inexpensive and flexible, it can perform many basic time-related functions including oscillators, one-shot pulse generators and frequency dividers. To use the 555 IC, first look at its data sheet and learn its basic operating parameters, then practice building circuits on a breadboard. This will give you enough experience to put the 555 to use in circuits of your own design.
Instructions
1. Study the 555 timer's data sheet thoroughly. It lists the circuit's current and voltage requirements, typical performance specifications and the functions of each of its eight pins. Pay close attention to the applications section. These are general examples of how you can use the IC.
2. Read the data sheet section describing the 555's timing network. A capacitor and one or two resistors determine the time period of the IC's pulse output. For example, the frequency of the 555's astable mode is determined by the following formula:
T = .693 x C x (Ra + 2Rb)
T is time in seconds, C is the capacitor's value in farads, and Ra and Rb are the ohm values for two resistors.
3. Understand the 555's modes of operation. Depending on how you configure the 555, it can be used in different ways. The astable mode is a pulse generator where the timing network described in Step 2 determines the pulse's duty cycle and period. You can use this to make a tone generator, a slow clock pulse for a digital circuit or to flash an LED.
The 555's monostable mode, or one-shot, generates a pulse with a specific on time when you trigger the IC at pin 2. This is useful anytime you need to turn something on for an exact period of time. In this case, the timing network determines the 555's on time.
You can also configure the IC for a bistable mode. This has two triggers, a set and a reset. The set trigger turns the circuit on, reset turns it off. This serves as an electronic latch or simple memory circuit. The bistable mode doesn't use a timing network.
4. Build several circuits with the 555 on a prototype breadboard using the application notes as a starting point. Try different values of resistors and capacitors in the timing network to see their effect on frequency and duty cycle. Use the 555's output at pin 3 to drive an LED in series with a 150-ohm current limiting resistor, and examine the output and timing network waveforms on an oscilloscope.
Tags: timing network, data sheet, astable mode, bistable mode, duty cycle