You could put a sample-and-hold circuit on the output of each DAC. The output voltages of the sample-and-hold circuits could be held while the the software changes one DAC voltage then the other. A GPIO digital output would control both sample-and-hold circuits so their outputs would change simultan...

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'm getting only -40mV. Is that measured with a scope or meter. That was measured with a scope with 4kHz signal. There's no negative voltage if I drop the GPIO drive stre...

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'm getting only -40mV but no negative voltage if I reduce the GPIO drive strength to the lowest option.

mzimmers wrote:-- if I set the timer to 13 bits, and the duty to 0x1fff, shouldn't I expect this to work (at maximum volume)?

To get 50% duty cycle square wave, I would expect to set duty to 50% of 2^13 = 0x1000.

It would help if you provide a link to the type of buzzer you are using. It sounds to me as if it's probably a piezo transducer such as this. If so, drive it directly from a GPIO, not through a transistor.

mzimmers wrote:I've discovered that most of the antennas that meet our size requirements are of very little gain (1-2 dBi) . . . .

ESP32 modules may not have such a good radiation pattern as omnidirectional aerials.

Below shows results of measurement of output voltage v. current for drive strength capabilities 0, 1, 2 and 3 (2 is the default). VIgraph.png The measurements were made with the following resistances: infinite, 2kΩ, 1kΩ, 470Ω, 220Ω, 150Ω, 100Ω, 47Ω and 0Ω. But for strengths 2 and 3 the minimum resis...

In my view the main thing that needs sorting out for the next chip is the analogue to digital converter (ADC). The issues with the ADC at present are: 1) Severe non-linearity with 11dB attenuation; 2) With a fixed input voltage, the digital readings vary significantly from one sample to the next (I ...

Neither 40mA nor 12mA applies to DAC outputs.

The issue is described here under "Minimising Noise" . . . . http://esp-idf.readthedocs.io/en/latest/api-reference/peripherals/adc.html#adc-api-adc-calibration It is really very poor. The Arduino Atmel processors are very much better. Beware also that I find linearity when the attenuation is set to ...