https://play.google.com/store/apps/details?id=com.keuwl.functiongenerator
I was able to program it to put out a 1KHz pulse of 100mS duration once per second, which was perfect for making transmit latency measurements. It is remarkably flexible, with two channels that can be assigned to the left and right outputs, and a wide variety of waveforms and options for noise, sweeps, pulses, etc.
I had to make a cable that went from the tablet headphone output to my microphone input, but that was easy. I had the connectors, so the entire thing was free

73!
Scott