Interference when connecting a piezo tweeter

[gmarocco]

I am building an ultrasonic generator with a dual frequency (25kHz and 36kHz). When the tweeter is not connected, the circuit works fine. When I connect the tweeter at the H-Bridge, I notice that that the frequency generated by U6 (NE555) has moved to 70kHz. Moreover, the square wave generated by U8 (NE555) has no more a period of 3s but of 0.1s. Should I connect an inductance at one side of the tweeter? Which is a suitable value?

The tweeter I have tried to connect is the following: **broken link removed**

ThanksView attachment ultrasound generation.pdf

 

[barry]

My guess is that you are pulling your power supply down. You might be getting some shoot-through in your bridge.