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555 Timer Pinout (NE555)

NE555 timer · DIP-8 / SOIC-8

The 555 timer in its 8-pin form: two comparators with thresholds at one third and two thirds of the supply, a flip-flop and a discharge transistor. Wire pins 2, 6 and 7 one way for a one-shot pulse, another way for an oscillator.

Checked against the KiCad library and datasheet on

NE555 timer pinout: KiCad footprint Package_DIP:DIP-8_W7.62mm seen from the top, beside the KiCad library symbol Timer:NE555P with every pin number and name
The KiCad NE555P symbol groups the pins by job, not by number: TRIG (2) and THRES (6) on the left with RESET (4) and DISCH (7), OUT (3) on the right. The footprint shows where those numbers land on the package. Exported from the KiCad 9 libraries (Timer:NE555P, Package_DIP:DIP-8_W7.62mm). Open full size

Pin by pin

PinNameFunction
1GNDGround
2TRIGStarts a timing cycle when pulled below 1/3 VCC; the output goes high
3OUTOutput; sources or sinks up to about 200 mA
4RESETActive low. Tie to VCC when not used
5CONTControl voltage, sits at 2/3 VCC. TI's example circuits put 10 nF from it to ground
6THRESEnds the cycle when it rises above 2/3 VCC; the output goes low
7DISCHOpen-collector discharge: shorts the timing capacitor to ground while the output is low
8VCCSupply, 4.5 V to 16 V for the bipolar NE555

Things that catch people out

  • A floating RESET (pin 4) resets the timer at random. Tie it to pin 8.
  • The bipolar NE555 draws a sharp current spike from the supply every time the output switches. Decouple pin 8 with 100 nF plus 10 µF or more beside the chip.
  • Oscillator (astable): R1 from VCC to pin 7, R2 from pin 7 to pins 6 and 2 joined, C from there to ground. f ≈ 1.44 / ((R1 + 2·R2)·C). One-shot (monostable): t ≈ 1.1·R·C.
  • CMOS versions (TLC555, LMC555, ICM7555) have the same pinout and draw far less current. Most start at lower voltages (the TLC555's C grade from 2 V, the LMC555 from 1.5 V), but none drives 200 mA from pin 3: the TLC555 sinks about 100 mA and sources about 10 mA.

Putting the NE555 timer on a PCB

  • Keep the timing capacitor's loop short: from pins 6 and 2 to the capacitor and straight back to pin 1. Do not share that ground return with whatever pin 3 is driving.
  • Put the 10 nF on pin 5, if you fit one, and the supply decoupling on pin 8 right at the package.
  • If pin 3 drives a relay or motor, add the flyback diode at the load and give that current its own path to the supply.

Common questions

Is the NE555 pinout the same as the LM555 and TLC555?
Yes. The 8-pin 555 timers from every maker share one pinout, bipolar and CMOS alike. The NE556 is two timers in a 14-pin package and has a different pinout.
What does pin 5 on a 555 do?
It is the internal 2/3 VCC threshold, brought out. Driving it shifts both thresholds, which changes the timing (that is how a 555 does voltage-controlled frequency). If you do not use it, TI's example circuits bypass it with 10 nF to ground, which usually improves noise immunity.
Why does my 555 circuit reset or glitch at random?
Usually a floating RESET pin or missing supply decoupling. Tie pin 4 to VCC and put 100 nF plus a larger capacitor across pins 8 and 1 at the chip.

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Sources

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