I.C NE555

Assalammualaikum..

An I.C NE555 is a component for our project which is Wet Diaper Detector (W.D.D). The purpose of using this component is to make a time delay or oscillation when the sensor detect the wetness on the diaper. Actually, the NE555 is a monolithic timing circuit that is highly stable controller able to producing accurate time delays.  

Figure 1.0 Image of NE555 

In time delay (operation mode), highlights in here, the time is controlled by one external capacitor and resistor. The circuit may be triggered and reset on falling waveform. the output structure can source and sink up to 200mA.

The NE555 is available in lastic and ceramic package with 8 pin connection. The image of NE555 is as below:

Figure 1.1 Pin connection from top view 

Figure 1.2 Block Diagram NE555

By referring to the figure 1.1 and 1.2 pin connection from top view and block diagram NE555:

1. Pin number one is the ground of the I.C. 

It connects to the 0V power supply.

2. Pin number two is the trigger in the circuit. 

Pin 2 has control over pin 6. 

If pin 2 is LOW and pin 6 LOW, output goes and stays HIGH. 

If pin 6 HIGH and pin 2 goes LOW, output goes LOW while pin 2 LOW. 

This pin has a very high impedance (about 10M) and trigger about 1uA.

3. Pin number three is the output. 

Pin 3 and pin 7 are 'in phase'. 

Goes HIGH (about 2V less than rail) and LOW (about 0.5V less than 0V) and will deliver up to 200mA.

4. Pin number four connected to pin number 8. 

Connected HIGH via 100k. It must be taken below 0.8V to reset the chirp.

5. Pin number five is the pin that is not connected to any pin or circuit.

A voltage applied to this pin will vary the timing of the RC network.

(quite considerably)

6. Pin number six is the threshold.

This pin has a very high impedance (about 10M) and will trigger with about 0.2uA.

7. Pin number seven is the discharge.

Goes LOW when pin 6 detects 2/3 voltage but pin 2 must be HIGH. 

If pin 2 is HIGH, pin 6 can be HIGH or LOW and pin 7 remains LOW. 

Goes OPEN (HIGH) and stays HIGH when pin 2 detects 1/3 rail voltage (even as a LOW pulse) when pin 6 is LOW. 

Pin 3 and 7 are 'in phase'. 

Pin 7 is equal to pin 3, but pin 7 not go high - it goes OPEN. 

But it goes LOW and will sink about 200mA.  

8. Pin number eight is the voltage supply.

It connects to the positive power supply (Vs). 

This can be any voltage between 4.5V to 15 DC, but commonly it is 5V DC when working with digital ICs.

Each of the pins is connected to the circuit which consists of over 20 transistors, 2 diodes and 15 resistors.