Real View
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.
Supply & groundTiming inputsOutputsControl & reset
NE555PPDIP-8Top view
NE555DSOIC-8Top view · dot marks pin 1
Click a lead or use the arrow keys. Top view
PIN 1 · Supply & 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 & ground
PowerVCC
Function
Positive supply.
How to connect
Use 4.5–16 V, with local supply decoupling.
At a glance
Bipolar timer
The capacitor moves between two thresholds, and the output changes state each cycle.
4.5–16 VRecommended supply
2 astable / monostableTiming modes
0–70 °CAmbient range
8 pinsPackage
Operating profile
NE555P
Operating conditions
Key parameters and their test conditions
- Supply
- 4.5–16 VConditions / notes: Recommended for NE555
- Ambient
- 0–70°CConditions / notes: NE555 grade
- Output
- Up to ±200 mAConditions / notes: Do not ignore output drop or package dissipation
- Supply absolute maximum
- 18 VConditions / notes: Stress limit, not an operating target
Package details
Follows the selected physical package
- 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
Connections by function
Select a pin to open its function, electrical notes and wiring guidance.
Supply & ground2 pins
Timing inputs2 pins
Outputs2 pins
Control & reset2 pins
Supply & ground2 pins
Timing inputs2 pins
Outputs2 pins
Control & reset2 pins
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.
The astable equations describe the standard circuit. Real timing also depends on tolerance, leakage and the device limits.
Pin reference
Select a pin to explore its function and connection.
8 pins
| Pin | Signal | Type | Function |
|---|---|---|---|
| GND | Ground | Circuit reference. | |
| TRIG | Input | Starts a timing cycle below roughly VCC/3. | |
| OUT | Output | Timer output. | |
| RESET | Input | Active-low reset overrides the timing cycle. | |
| CONT | Control | Adjusts comparator reference levels. | |
| THRES | Input | Ends the high interval above roughly 2VCC/3. | |
| DISCH | Open collector | Discharges the timing capacitor during the low interval. | |
| VCC | Power | Positive supply. |
No pins match. Try a signal name or choose All pins.
Operating conditions
Reviewed manufacturer specifications
Manufacturer specifications 4 parameters
| 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
| 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
| 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.
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