Description :

this project followed by 3 other projects which all are in a same category with different approaches. we just trying to make/simulate nightly crickets chirping which is one of the loveliest natural sounds for most peoples. all provided projects in this group provides realistic sound as best as possible with no filtering no amplifying and using fewest cheapest strongest components. OK enough boasting lets do it!

Timer 555 :

we have 3 different 555 ic's used in this project where all of them are in Astable mode. we just compine two ic's into single one for more fun so you see one NE556 (which is two NE555) and one NE555. skip explaining timer 555 as there is many useful project's/tutorial's on it available with taking a look in instructables.com. but let me provide some usefull links at least :

555 Astable calculator

https://www.instructables.com/id/555-Timer/

all we do is following the Astable calculation to provide desired frequencies. at step1 i placed an image that is a very approximate preview of chirping result which demonstrates duty and frequency used just with changing two resistors and capacitor per IC.

Supplies

IC

IC1 1 x NE555
IC2 1 x NE556

Resistors

R(2,4,5,6,7,9) 6 x 10 KΩ
R(1,3) 2 x 4.7 KΩ
R8 1 x 3.3 KΩ

Capacitors

C(1,7) 2 x ceramic 4.7 nF
C(2,3,4) 3 x ceramic 10 nF
C5 1 x electrolytic 3.3 µF
C6 1 x electrolytic 47 µF

Transistors

Q1 1 x NPN 2n2222A
Q2 1 x PNP ss9012

Other

BZ1 1 x Passive Buzzer (look at schema to replacement availability)

Step 1: Circuit

every thing is clear. its your choice to use 3x555 ic's or just one 556 + one 555 for simplicity.as you see two marked regions on schema, we used Q1 to invert IC1 output. and other region suggests replacing bounded circuit with an existing passive buzzer module for less effort.