NE555Bipolar timer
Turn a resistor and capacitor into a clock.
NE555 is an eight-pin timer for repeating pulses or a single timed output. An external resistor-capacitor network sets the timing; internal comparators and a latch control the output. Choose NE555P in PDIP-8 or NE555D in SOIC-8. Both use the same eight-pin mapping. The example is a 5 V astable LED flasher.
8Physical pins
NE555PPDIP-8
Manufacturer-referencedTexas Instruments
Pin diagram
Select a pin to explore its connection
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NE555PPDIP-8Top view
NE555DSOIC-8Top view · dot marks pin 1
Click a lead or use the arrow keys. Top view
PIN 1 · Ground
GroundGND
Function
Circuit reference.
How to connect
Connect to supply return.
PIN 2 · Timing inputs
InputTRIG
Function
Starts a timing cycle below roughly VCC/3.
How to connect
For astable operation, join TRIG to THRES at the capacitor node.
PIN 3 · Outputs
OutputOUT
Function
Timer output.
How to connect
Drive the LED through a current-limiting resistor.
Electrical note
Output is not rail-to-rail; check loading and dissipation.
PIN 4 · Control & reset
InputRESET
Function
Active-low reset overrides the timing cycle.
How to connect
Tie to VCC when reset is unused.
PIN 5 · Control & reset
ControlCONT
Function
Adjusts comparator reference levels.
How to connect
A small bypass capacitor to ground reduces noise when control is unused.
PIN 6 · Timing inputs
InputTHRES
Function
Ends the high interval above roughly 2VCC/3.
How to connect
Connect to the timing capacitor node.
PIN 7 · Outputs
Open collectorDISCH
Function
Discharges the timing capacitor during the low interval.
How to connect
Connect to the junction of the astable timing resistors.
PIN 8 · Supply
PowerVCC
Function
Positive supply.
How to connect
Use 4.5–16 V, with local supply decoupling.
Key specifications
The capacitor moves between two thresholds, and the output changes state each cycle.
Recommended supply4.5–16 V
Timing modes2 astable / monostable
Ambient range0–70 °C
Package8 pins
Package details
NE555P · PDIP-8
| Property | Details |
|---|---|
| Manufacturer | Texas Instruments |
| Part number | NE555P |
| Package | PDIP-8 |
| Connections | 8 pins |
| Mounting | Through-hole |
| Lead pitch | 2.54 mm |
| Package code | P |
| Thermal reference | See manufacturer thermal table |
Operating conditions
Reviewed manufacturer specifications
Manufacturer specifications 4 parameters
Scroll sideways to see all columns.
| Parameter | Value | Conditions / notes |
|---|---|---|
| Supply | 4.5–16 V | Recommended for NE555 |
| Ambient | 0–70°C | NE555 grade |
| Output | Up to ±200 mA | Do not ignore output drop or package dissipation |
| Supply absolute maximum | 18 V | Stress limit, not an operating target |
No specifications match. Try a parameter name or a unit.
Timing equations
Reviewed manufacturer specifications
Manufacturer specifications 5 parameters
Scroll sideways to see all columns.
| Parameter | Value | Conditions / notes |
|---|---|---|
| High interval | tH ≈ 0.693 (RA + RB) C | Standard astable circuit |
| Low interval | tL ≈ 0.693 RB C | Standard astable circuit |
| Frequency | f ≈ 1.44 / ((RA + 2RB) C) | R in ohms; C in farads |
| Duty cycle | D ≈ (RA + RB) / (RA + 2RB) | Greater than 50% in this basic circuit |
| Single pulse | t ≈ 1.1 RC | Monostable circuit |
No specifications match. Try a parameter name or a unit.
Astable worked example
Reviewed manufacturer specifications
Manufacturer specifications 4 parameters
Scroll sideways to see all columns.
| Parameter | Value | Conditions / notes |
|---|---|---|
| RA / RB / C | 10 kΩ / 68 kΩ / 10 µF | Illustrative values |
| High time | ≈0.541 s | Calculated ideal interval |
| Low time | ≈0.471 s | Calculated ideal interval |
| Frequency | ≈0.99 Hz | Approximate; tolerance changes the result |
No specifications match. Try a parameter name or a unit.
Connections by function
Select a pin for its function, connection guidance and electrical notes.
Ground1 pin
Timing inputs2 pins
Outputs2 pins
Control & reset2 pins
Supply1 pin
Ground1 pin
Timing inputs2 pins
Outputs2 pins
Control & reset2 pins
Supply1 pin
NE555 at a glance
Follow the labeled connections and functional stages
How it works
3 stages · Explore one step at a time
Power and control
Connect pins 8 and 4 to +5 V, pin 1 to ground. Use a 100 nF supply bypass and a 10 nF capacitor from CONT to ground.
Build the timing network
RA = 10 kΩ, RB = 68 kΩ and C1 = 10 µF. Join pins 2 and 6 to the capacitor node; pin 7 connects to the resistor junction. The capacitor’s positive plate faces the timing node.
Read the cycle
Nominal high time is 0.693 × (RA + RB) × C1 = 0.541 s. Low time is 0.693 × RB × C1 = 0.471 s. The LED flashes about once per second; tolerance changes the exact result.
Step 1 of 3
NE555 in a circuit
A complete wiring example with numbered pins, component values and local ground symbols.
Connect it, step by step
Follow the component values and pin connections
Power and control
Connect pins 8 and 4 to +5 V, pin 1 to ground. Use a 100 nF supply bypass and a 10 nF capacitor from CONT to ground.
Build the timing network
RA = 10 kΩ, RB = 68 kΩ and C1 = 10 µF. Join pins 2 and 6 to the capacitor node; pin 7 connects to the resistor junction. The capacitor’s positive plate faces the timing node.
Read the cycle
Nominal high time is 0.693 × (RA + RB) × C1 = 0.541 s. Low time is 0.693 × RB × C1 = 0.471 s. The LED flashes about once per second; tolerance changes the exact result.
Inside NE555
A labeled functional schematic with the important signal paths.
Explore the circuit
Select a stage to see its role and connections
Create the thresholds
Three nominal 5 kΩ resistors establish 1/3 and 2/3 of VCC. The control pin provides access to the upper reference.
Compare and remember
TRIG below 1/3 VCC sets the latch. THRES above 2/3 VCC resets it. Active-low RESET overrides the timing cycle.
Drive and discharge
The output stage follows the latch. In the low state, the discharge transistor connects pin 7 toward ground and empties the timing capacitor through RB.
Selected packagePDIP-8NE555P
Physical connections8 pinsPackage-specific numbering
Reference collection4 tables13 parameters & pin functions
Pin reference
Signal names, electrical functions and connection guidance
Physical pin numbers8 pins
Scroll within the table to see all columns and rows.
| Pin | Signal | Type | Function & connection |
|---|---|---|---|
| GND | Ground | Circuit reference.Connection guidanceConnect to supply return. | |
| TRIG | Input | Starts a timing cycle below roughly VCC/3.Connection guidanceFor astable operation, join TRIG to THRES at the capacitor node. | |
| OUT | Output | Timer output.Connection guidanceDrive the LED through a current-limiting resistor. Output is not rail-to-rail; check loading and dissipation. | |
| RESET | Input | Active-low reset overrides the timing cycle.Connection guidanceTie to VCC when reset is unused. | |
| CONT | Control | Adjusts comparator reference levels.Connection guidanceA small bypass capacitor to ground reduces noise when control is unused. | |
| THRES | Input | Ends the high interval above roughly 2VCC/3.Connection guidanceConnect to the timing capacitor node. | |
| DISCH | Open collector | Discharges the timing capacitor during the low interval.Connection guidanceConnect to the junction of the astable timing resistors. | |
| VCC | Power | Positive supply.Connection guidanceUse 4.5–16 V, with local supply decoupling. |
No pins match these filters. Try another signal name or reset the filters.
Operating conditions
Reviewed manufacturer specifications
Manufacturer-referenced values4 parameters
Scroll within the table to see all columns and rows.
| Parameter | Value | Conditions / notes |
|---|---|---|
| Supply | 4.5–16 V | Recommended for NE555 |
| Ambient | 0–70°C | NE555 grade |
| Output | Up to ±200 mA | Do not ignore output drop or package dissipation |
| Supply absolute maximum | 18 V | Stress limit, not an operating target |
No specifications match. Try a parameter name or a unit.
Timing equations
Reviewed manufacturer specifications
Manufacturer-referenced values5 parameters
Scroll within the table to see all columns and rows.
| Parameter | Value | Conditions / notes |
|---|---|---|
| High interval | tH ≈ 0.693 (RA + RB) C | Standard astable circuit |
| Low interval | tL ≈ 0.693 RB C | Standard astable circuit |
| Frequency | f ≈ 1.44 / ((RA + 2RB) C) | R in ohms; C in farads |
| Duty cycle | D ≈ (RA + RB) / (RA + 2RB) | Greater than 50% in this basic circuit |
| Single pulse | t ≈ 1.1 RC | Monostable circuit |
No specifications match. Try a parameter name or a unit.
Astable worked example
Reviewed manufacturer specifications
Manufacturer-referenced values4 parameters
Scroll within the table to see all columns and rows.
| Parameter | Value | Conditions / notes |
|---|---|---|
| RA / RB / C | 10 kΩ / 68 kΩ / 10 µF | Illustrative values |
| High time | ≈0.541 s | Calculated ideal interval |
| Low time | ≈0.471 s | Calculated ideal interval |
| Frequency | ≈0.99 Hz | Approximate; tolerance changes the result |
No specifications match. Try a parameter name or a unit.
No matching rowsTry a pin name, parameter, unit or test condition, or reset the filters.
LED flasher
A timing network produces regular output pulses. Keep a resistor in series with the LED.
Manufacturer application guideOne-shot pulse
Monostable operation creates one timed interval per valid trigger.
Manufacturer application guideTake it into ProTech
Find NE555 in the Components Library to place its schematic symbol and connect its pins.
Simulation model available · Open the working exampleOpen ProTech