Well the LM386 with 200 gain (cap across pins 1 and 8 works rather well.
Now seeing how a bunch of old bats like me hang out here (lol) was thinking of having this BAT APP output sound either randomly or every 10 minutes or ??
This would "confuse" the bats maybe plus allow the unit to last longer instead of running 24/7
Using the CRITTER RIDDER code for a 18F1320 (programed to randomly output desired frequencies, in this case 18-26khz) so adding a timer would be a simple matter of a few lines of code.
Looking at other repellent circuits that use a 555, 4017, 4013 etc, using a pic saves lots of silicone chips.
any suggestions on time on/time off?