NE555 datasheet and Pinout, NE555 circuits generates square waves

 NE555 Datasheet

1. What is NE555 timer?

The NE555 timer IC is a highly stable integrated circuit belonging to the 555 series of timing ICs, commonly used in timers, pulse generators, and oscillation circuits. This IC was released by Signals Corporation around 1971 and was the only very fast and commercialized Timer IC at that time. Due to its ease of use, low cost, and good reliability, it is still widely used in the design of electronic circuits to this day.

The NE555 timer mainly consists of a comparator, SR latch, R-S trigger, digital to analog converter, and other parts. Due to its excellent performance, it is widely used in various timing control circuits, such as stable oscillators, monostable triggers, PWM generators, slope integral A/D conversion, etc.

2. NE555 Features

From the data table of NE555, we can know that IC 555 has the following characteristics

● Timing From Microseconds to Hours

● Astable or Monostable Operation

● Adjustable Duty Cycle

● TTL-Compatible Output Can Sink or Source

● Up to 200 mA

● On Products Compliant to MIL-PRF-38535,All Parameters Are Tested Unless Otherwise Noted. On All Other Products, Production Processing Does Not Necessarily IncludeTesting of All Parameters.

3.Applications

● Fingerprint Biometrics

● lris Biometrics

● RFID Reader

Data from NE555 spec sheet

4. NE555 Pinout

We can obtain its pinout information from the NE555 spec sheet

NE555 Pinout

NE555 Pin Functions

5. Usage of NE555 IC

Power connection: The NE555 IC can operate at a power supply voltage of 4.5V to 18V. VCC is connected to the positive pole, and GND is connected to the negative pole.

Timing function: By connecting resistors and capacitors to the corresponding pins, the NE555 IC can be configured to be used as a timer.

Trigger and reset: The NE555 IC can be placed in the trigger or reset state through external circuits to achieve different functions.

Output: The NE555 IC has an open drain output that can drive LEDs, relays, or other loads.

6. NE555 circuits usage tips

Stability: To ensure the stability of the circuit, it is recommended to use resistors and capacitors with a precision of 1%.

Power decoupling: Add a 0.1 between VCC and GND μ The ceramic capacitor of F can improve the stability of the circuit.

Protect output: To protect the output of the NE555 circuits from damage, an appropriate current limiting resistor can be added.

Extended functionality: Through innovative design of external circuits, more complex functions can be achieved, such as adjustable duty cycle and frequency.

7. Advantages and disadvantages of NE555

Advantages:

Multifunctionality: The NE555 can be configured to achieve various functions, such as timers, pulse generators, and oscillators.

Wide power supply voltage range: can operate at a power supply voltage of 4.5V to 18V.

Affordable price: As NE555 has been produced for decades, its price is relatively low.

Easy to use: The required functions can be achieved through simple external component connections.

Disadvantages:

Limited speed: Compared to modern microcontrollers, the NE555 has limited speed.

Temperature stability: Its performance may be affected by temperature.

Single function limitation: Although its functionality can be extended through external circuits, its single function capability may be limited compared to dedicated ICs.

8. NE555 alternatives and selection suggestions

Alternative: Modern microcontrollers or other specialized ICs can be considered as substitutes for NE555 to achieve more complex and high-speed functions.

Selection suggestion: When selecting an alternative model, factors such as required functionality, speed, power supply voltage range, size, and cost need to be considered. Ensure that the selected model meets practical application requirements and provides better performance and stability. For example, if complex functions or high-speed applications need to be implemented, modern microcontrollers can be chosen; If only simple timing or pulse functions are needed, and cost is a factor to consider, then NE555 is still a good choice.

9. Generating square waves using NE555 circuits

Firstly, let's take a look at the internal structure of the NE555 circuits:

C1 and C2 are two operational amplifier comparators, and the internal resistance values of these three resistors are the same, all 5K ohms. The one behind is an SR latch, the one behind is an inverter, and there is also an NPN transistor inside.

Let's take a look at the basic parameters. From the resistance voltage divider, we can know that the voltage VI1 at the same phase end of comparator C1 is 2/3VCC, and the voltage VI2 at the opposite phase end of C2 is 1/3VCC. Everyone should know that the output of an operational amplifier comparator is VCC when the voltage at the same phase end is greater than the voltage at the opposite phase end, and 0 when the voltage at the same phase end is less than the voltage at the opposite phase end.

For this SR latch

NE555 circuits can be used to connect Schmitt triggers, monostable triggers, and multi harmonic oscillators.

To generate square waves, NE555 circuits needs to be connected to a multi harmonic oscillator. Let's take a look at the circuit diagram, everyone

This circuit mainly needs to understand the charging and discharging circuit diameter of the capacitor. When charging a capacitor, it is charged through R1 and R2. When discharging, when Q1 conducts, the capacitor is discharged through R2.

When charging capacitors, when VI1=VI2<1/3VCC, VO=1, Q1 is turned off,

When 1/3VCC< VI1=VI2<2/3VCCtime, VO=1,

When VI1=VI2>2/3VCC, VO=0, Q1 conducts, and the capacitor discharges. When 1/3VCC<VI1=VI2<2/3VCC, VO=0,

When the discharge is placed at VI1=VI2<1/3VCC, VO=1, Q1 is turned off, and the capacitor is charged,

By repeatedly charging and discharging in this way, the output VO will output a square wave.

Let's take a look at parameter calculations.

Calculation formula for capacitor charging from V1 to V2

The time t for the capacitor to charge from V1 to V2 is RC * l n ((VCC-V1)/(VCC-V2))

The time it takes for the capacitor to discharge from V1 to V2

T=RC * ln (V1V2)

Charging time/square wave high-level time

T1=(RA+RB) * C * ln2

Discharge time/square wave low-level time

T2=RB * C * ln2

cycle

T=(RA+2RB) C * ln2

Duty cycle

Q=(RA+RB)/(RA+2RB)

Everyone can see from the formula of this duty cycle that the duty cycle of this square wave is fixed and not adjustable. In order to obtain an adjustable duty cycle, we need to separate the charging and discharging paths of the capacitor. The following circuit is obtained.

The charging path is this,

The discharge path is this,

We can change the duty cycle of the output square wave by adjusting the position of the center tap of the potentiometer. The parameters of this circuit are as follows:

Charging time/square wave high-level time T1=(RA+Rw1) * C * ln2

Discharge time/square wave low-level time T2=(RB+Rw2) * C * ln2

Cycle T=(RA+RB+Rw) C * ln2

Duty cycle q=(RA+Rw1)/(RA+RB+Rw)