PAGE 076 OF 150 · TIMERS, FLASHERS & DIMMING
The 555 Timer Basics
The 555 is a classic timing chip with three common modes.
LED SYMBOLTriangle points from anode to cathode; the arrows show light leaving the part.
What the 555 is
The 555 is an 8-pin timer chip used for blinkers, delays and pulses. It compares a capacitor's voltage against one third and two thirds of the supply.
Pins
- 1 ground, 2 trigger, 3 output, 4 reset
- 5 control, 6 threshold, 7 discharge, 8 supply
Details
The standard NE555 works from about 4.5 to 16 V and its output can supply up to around 200 mA, enough for an LED with a resistor. Common modes are astable (repeating), monostable (one pulse) and bistable (flip-flop).
REMEMBER
Switching an LED on and off quickly can look like steady dimmer light.Try it yourself
Sketch the circuit on paper first, calculate the values, then build it on a solderless breadboard using a low-voltage supply. Measure with a multimeter before you make anything permanent.
Explore LED clocks, stopwatches and electronics at cosycom.com.