NE555 TIMER IC

Overview

NE555 / LM555 Timer IC — one of the most versatile and widely used integrated circuits ever manufactured. A precision timing IC capable of operating as a monostable multivibrator (one-shot timer), astable multivibrator (oscillator/clock generator), or bistable multivibrator (flip-flop). Used in millions of applications including LED flashers, PWM generators, tone generators, delay circuits, pulse generators, motor speed control, and signal processing. Compatible with 5V to 15V supply, making it suitable for Arduino, ESP32, and standalone circuits.

Specifications

Parameter	Value
Model	NE555 / LM555 / SE555
Type	Precision Timer IC
Supply Voltage	4.5V – 16V
Output Current	200mA (source/sink)
Timing Accuracy	±1%
Temperature Stability	0.005% per °C
Operating Frequency	DC to 500kHz
Output Voltage (HIGH)	VCC – 1.7V
Output Voltage (LOW)	0.1V
Trigger Current	0.5μA
Reset Current	0.1mA
Power Dissipation	600mW
Package	DIP-8 (Through-hole)
Operating Temperature	0°C to +70°C (NE555)
Military Grade	-55°C to +125°C (SE555)

Pin Configuration

Pin	Name	Description
1	GND	Ground (0V)
2	TRIG	Trigger input — starts timing when < 1/3 VCC
3	OUT	Output — HIGH or LOW depending on state
4	RESET	Reset (active LOW) — tie to VCC if unused
5	CTRL	Control voltage — tie 10nF cap to GND if unused
6	THRES	Threshold — stops timing when > 2/3 VCC
7	DISCH	Discharge — open collector output for timing capacitor
8	VCC	Power supply (4.5V – 16V)

Operating Modes

Mode 1 — Astable (Oscillator / Clock Generator)

Continuously oscillates — generates square wave output. No external trigger needed. Used for LED flashers, tone generators, PWM.

Frequency Formula: f = 1.44 / ((R1 + 2×R2) × C) Duty Cycle = (R1 + R2) / (R1 + 2×R2) × 100%

Astable Circuit: VCC ── R1 ── Pin7 ── R2 ── Pin2/6 │ C ── GND Pin4 (RESET) → VCC Pin5 (CTRL) → 10nF → GND

Mode 2 — Monostable (One-Shot Timer)

Outputs a single pulse of defined duration when triggered. Used for delay circuits, debouncing, pulse stretching.

Pulse Width Formula: T = 1.1 × R × C

Example: R=10kΩ, C=10μF → T = 1.1 × 10,000 × 0.00001 = 0.11 seconds

Monostable Circuit: VCC ── R ── Pin6/7 │ C ── GND Pin2 (TRIG) ── Button ── GND (trigger on LOW pulse) Pin4 (RESET) → VCC Pin5 (CTRL) → 10nF → GND

Mode 3 — Bistable (Flip-Flop / Latch)

Output latches HIGH or LOW based on trigger and reset inputs. Used for switch debouncing, latching circuits.

Pin2 (TRIG) ── Button1 ── GND (SET) Pin4 (RESET) ── Button2 ── GND (RESET) No timing components needed

Timing Reference Table (Monostable)

R Value	C Value	Pulse Width
10kΩ	1μF	11ms
10kΩ	10μF	110ms
10kΩ	100μF	1.1s
100kΩ	10μF	1.1s
1MΩ	10μF	11s
1MΩ	100μF	110s

Frequency Reference Table (Astable)

R1	R2	C	Frequency
1kΩ	1kΩ	100nF	4.8kHz
10kΩ	10kΩ	100nF	480Hz
10kΩ	10kΩ	10μF	4.8Hz
1kΩ	47kΩ	10μF	1.5Hz
10kΩ	100kΩ	100μF	0.07Hz

LED Flasher Circuit (Astable)

VCC (9V) │ R1 (1kΩ) │ Pin8 (VCC) ──────────── VCC Pin4 (RESET) ─────────── VCC Pin1 (GND) ───────────── GND Pin7 (DISCH) ── R1(1kΩ) ─── VCC Pin7 (DISCH) ── R2(47kΩ) ── Pin2/6 Pin2/6 ── C(10μF) ─── GND Pin5 (CTRL) ── 10nF ─────── GND Pin3 (OUT) ── 470Ω ─ LED ─ GN

Flash rate: ~1.5Hz (slow blink)

Arduino Integration

Use 555 timer with Arduino for:

• Hardware PWM independent of Arduino processor
• High current LED driving (200mA vs Arduino's 40mA)
• Precise timing without software delays
• Motor speed control via hardware PWM

// Read 555 output frequency with Arduino
int pin555 = 2; // Connect 555 OUT to pin 2
volatile int count = 0;

void countPulse() { count++; }

void setup() {
  Serial.begin(9600);
  attachInterrupt(digitalPinToInterrupt(pin555), countPulse, RISING);
}

void loop() {
  count = 0;
  delay(1000);
  Serial.print("Frequency: ");
  Serial.print(count);
  Serial.println(" Hz");
}

PWM Motor Speed Control

VCC ── R1(1kΩ) ── Pin8 Pin7 ── R2(10kΩ pot) ── Pin2/6 Pin2/6 ── C(100nF) ── GND Pin3 (OUT) ── MOSFET Gate ── Motor Pin4,8 ── VCC Pin5 ── 10nF ── GND

Adjust pot R2 to vary PWM duty cycle and motor speed.

555 vs 556 vs 558

IC	Timers	Package	Notes
NE555	1	DIP-8	Standard single timer
NE556	2	DIP-14	Dual 555 in one package
NE558	4	DIP-16	Quad timer
LMC555	1	DIP-8	CMOS version, lower power
ICM7555	1	DIP-8	CMOS, works from 2V

NE555 vs LM555 vs SE555

Version	Temp Range	Grade
NE555	0°C to +70°C	Commercial
LM555	0°C to +70°C	Commercial (TI)
SA555	-40°C to +85°C	Industrial
SE555	-55°C to +125°C	Military

⚠️ Important Notes

• Pin 4 (RESET) — always tie to VCC if not used, or IC will not work
• Pin 5 (CTRL) — connect 10nF bypass capacitor to GND to reduce noise
• Output current 200mA — can directly drive LEDs, small relays, buzzers
• Timing capacitor — use non-polarized capacitor for small values, electrolytic for large
• Electrolytic capacitor polarity — positive lead to Pin 2/6, negative to GND
• Decoupling capacitor — add 100nF between VCC and GND near IC
• Maximum frequency — 500kHz, higher freq use CMOS version (LMC555)
• Avoid touching Pin 5 — sensitive control voltage input
• For 3.3V operation — use CMOS 555 (LMC555 or ICM7555), NE555 needs min 4.5V

Applications

• LED flasher and blinker circuits
• Tone and sound generator
• PWM motor speed control
• Servo signal generator
• Debounce circuit for buttons
• Delay timer relay control
• Pulse width modulator
• Clock signal generator
• Missing pulse detector
• Frequency divider
• Metronome and rhythm generator
• Touch switch circuit
• Dark/light activated switch
• Battery level indicator
• Arduino hardware timer extension