Alexis Polti gave us some tweeters he ordered. My goal was to determine the electrical characteristic of the tweeters in order to design the H-bridge.
As the tweeter acts as a capacitor, we’ll need to add a resistor in series with the tweeter in order to protect against intensity peaks the capacitor will generate when the voltage changes (i=C * du/dt).
So, I need to figure out what is the capacitance of the tweeter at the given frequency, so I can calculate the resistance value (it will act as a low-pass filter for the capacitor). With the tweeter was given a little circuit which generates the ultrasound frequency.
After soldering it (and figuring out that the short circuit was because I haven’t applied the erratum. Yes, the PCB was faulty), I have been able to measure the frequency output, the voltage, and the intensity of the tweeter. The strange thing is that even if the datasheet says it will generate a 23kHz frequency, I only see a 19kHz frequency with a very crappy signal (you can see the frequency by clicking on the image and zooming — I had only two hands to take the photo and connect the circuit 🙂 ).
I measured 6.7Vpp, 19.01kHz and 202uA. That means the capacity of the tweeter at 19.01kHz is 1.59 nF. So by using a resistor of 10kohm, the cutoff frequency will be over 40kHz which will be really fine.