- MAX232 VCC not connected. hand solder to VCC5.
- TXMUX VSS and MAX232 capacitor GNDs not connected. hand solder to GND.
- Too much voltage drop across AVCC isolation resistor. short.
- Omit R29, substitute R26 100k instead of 50k (or, R25 to 25k)
- AD5220 should have higher resistance
- Make R10 smaller
- Remove JTAG port, use a bootloader instead.
- Increase sonar TX power by a factor of 2.
I didn't realize why I put in R26 in until now: replace it with a tuned inductor to make the transmitter resonant. Apparently this does not work. I think the problem is that the piezo transducers are not particularly efficient capacitors. If a real capacitor is put in parallel with the transmitter and the inductor value is readjusted it should work but at this point I am more inclined to copy the tried-and-true circuit from Crunch.
More to come, unfortunately.