That was measured with a scope with 4kHz signal. There's no negative voltage if I drop the GPIO drive strength to minimum. I would not expect a piezo transducer to work well if it's just in series with the drain of a transistor but that should be OK for the electro-magnetic transducer.mikemoy wrote:Is that measured with a scope or meter.Archibald wrote:I'm getting only -40mV.mikemoy wrote:Just an FYI, it's not a good idea to drive a piezo electric device via a GPIO pin. Piezo devices can generate negative voltages.
I would recommend a kick-back diode (reference) with that electro-magnetic transducer to protect the transistor. I see its coil resistance is only about 16Ω.