NE555 – circuit examples

First set of eight 555 circuit examples including printed circuit board designs.

1) A timer with a fixed period

Basic wiring of the 555 circuit as a timer with a single button on START. The timing period is fixed by the value of components R1 and C1 to approximately 50s.

ne555 timer circuit
Img. 1: Circuit diagram

ne555 timer pcb
Img. 2: Layout of components

ne555 timer pcb
Img. 3: Printed circuit board

2) Timer with variable period

Complete wiring of a 555 circuit as a timer. The circuit contains both a START button and a STOP button, which can be used to end the timing prematurely. The timing period can be adjusted by potentiometer P1 in the range of approximately 1.1 to 120 seconds.

ne555 timer schematic
Img. 4: Circuit diagram

ne555 timer
Img. 5: Layout of components

ne555 timer
Img. 6: Printed circuit board

3) Touch-triggered timer

As the first connection of the timer, with the only difference that instead of the start button, a small metal plate is connected to the J5 connector. The timer is started by touching this pad. Of course, the circuit requires power from a mains adapter, or to connect the ground pole of the source (pin J2) to the ground, for example, on the radiator.

ne555 touch trigger
Img. 7: Circuit diagram

ne555 touch trigger
Img. 8: Layout of components

ne555 touch trigger
Img. 9: Printed circuit board

4) Sensor control with sound signaling

Touch control indicating the application of a finger with a sound signal. Of course, the circuit requires power from a mains adapter, or to connect the ground pole of the source (pin J2) to the ground, for example, on the radiator.

ne555 sensor control
Img. 10: Circuit diagram

ne555 sensor control
Img. 11: Layout of components

ne555 sensor control
Img. 12: Printed circuit board

5) Police horn

The connection faithfully imitates the sound of a police siren. Alternatively, it is possible to connect a resistor trimmer instead of resistor R4 and fine-tune the resulting tone.

ne555 police siren
Img. 13: Circuit diagram

ne555 police horn
Img. 14: Layout of components

ne555 police horn
Img. 15: Printed circuit board

6) Soil moisture measuring probe

The probe is inserted into, for example, a flower pot, and it is easy to determine soil moisture based on the pitch of the tone emitted.

ne555 soil moisure
Img. 16: Circuit diagram

ne555 soil moisure
Img. 17: Layout of components

ne555 soil moisure
Img. 18: Printed circuit board

7) Touch indicator

Another touch indicator, this time with an LED. Of course, the circuit requires power from a mains adapter, or to connect the ground pole of the source (pin J2) to the ground, for example, on the radiator.

ne555 touch indicator
Img. 19: Circuit diagram

ne555 touch indicator
Img. 20: Layout of components

ne555 touch indicator
Img. 21: Printed circuit board

8) Water level detector

If the electrodes on pins J3 and J4 are immersed in water, there is supply voltage at the output of the circuit (pin no. 3) and the LED is off. However, as soon as the electrodes emerge from the water, the output switches to approx 0V and LED D1 lights up.

ne555 water level detector circuit
Img. 22: Circuit diagram

ne555 water level detector
Img. 23: Layout of components

ne555 water level detector
Img. 24: Printed circuit board

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