Hi Wowowee,
It's difficult to say if the oscillator part will work, where are you
gonna find a 40 kHz crystal, or is it some kind of resonator ?
The - 3 dB point of the low-pass filter with the 100 k resistor and
the 50 pF capacitor is only about 32 kHz.
Only one comment, the output to the ultrasonic TX won't be of much
use because these transducers require a substantial amount of drive.
Remove both 220R resistors and replace them with the same drive
circuit driven by the previous "inverter" to form an H-bridge.
If you can't find a 40 kHz crystal you can always replace the
oscillator part with the following "no tune" circuit.
**broken link removed**
on1aag.
The oscillator part will not work because you used a nand gate
with a schmitt-trigger input and this kind of oscillator requires
the gate to operate in linear mode !
A 4011 will be a better choice for the oscillator part.