Versatile IC for timing, pulse generation and oscillation.
The 555 has two comparators, a flip-flop and a discharge transistor. Astable mode: f≈1.44/((R₁+2R₂)C); monostable pulse width T=1.1RC. Used for blinkers, delays, PWM and tone generation. CMOS versions use less power.
R=100 kΩ and C=10 µF monostable gives about 1.1 s.
The 555 timer is one of the most widely used chips, and it teaches the basics of timing, pulses and oscillation in a simple package.
Versatile IC for timing, pulse generation and oscillation.
The 555 timer is one of the most widely used chips, and it teaches the basics of timing, pulses and oscillation in a simple package.
Astable mode gives a repeating square wave, monostable gives a single timed pulse, and bistable acts as a flip-flop with a set and reset.
Choose the resistor and capacitor values in the timing equations for the mode you use, and remember the duty cycle depends on the two resistors.
Typical applications include building a flashing LED indicator with a 555 in astable mode, creating a one-shot delay for a door alarm and generating a PWM signal for a small fan speed control.
Study "Oscillators" first (topic 24 of 104 in Electronics & Embedded). It covers the groundwork this topic builds on.
Reference thresholds ⅓ and ⅔ V_cc. Duty cycle always above 50% in basic astable. Reset pin.
R=100 kΩ and C=10 µF monostable gives about 1.1 s.
The next topic is "Feedback in amplifiers", which builds directly on this one.
It is classed as Beginner in Electronics & Embedded (topic 25 of 104). It is an entry-level topic. It relies only on basic school mathematics and the ideas introduced earlier in this discipline.
Want to practise? Open the interactive course for quick checks, quizzes, simulations and progress tracking.