A simple 555 oscillator circuit that produces a square-wave oscillation, with a 50% duty cycle. The that can be simple 555 oscillator circuit operates at can be adjusted by altering the R1 and C1 values as shown in the table.
1 x 555 timer
1 x 200nF capacitor
1 x R1 resistor (as selected from table)
1 x C1 capacitor (as selected from table)