Ultrasonic oscillations which are generated by unmodulated ultrasonic transmitters commonly for remote control are usually affected from other ultrasonic sources in the media and that’s why we are giving a 500Hz modulated ultrasonic transmitter circuit here.
Voltage supply of the circuit is 9 Volts and any change of the value will change the frequency also. You can omit this difference by connecting a resistor between A and B nodes. You can find the value of the resistor by using this formula:
R = (Vsupply – 7V) / O.6 Kohm where Vsupply is the new supply voltage value.
The multivibrator generates 500Hz modulation frequency. To avoid the frequency differences , tolerance of the circuit should not exceed %5.
If the circuit components changed, then the frequency can be determined by using the formula below,
f = (1.44 x 1000) / (C2 x R3 x C3 x R2)
If C1 and C3 are nanofarads then R2 and R3 will be magaohms.