AVR-Chat

I'm working off of a schematic that I found on the web which is an
ultrasonic rangefinder utilizing a PIC... The transmitter section has
the PIC driving an Ultrasonic Transmiter at 40khz... The schematic shows
one side of the transmiter connected to one pin on the PIC and the other
side connected to another pin on the PIC.... I am doing this with a
Tiny15; shouldn't one side of the transmitter be connected to ground and
the other to the avr?  Do I need to use a resister or will the
transmitter draw a low enough current?  Should I use a transistor to
drive the transmitter?
Thanks,
Daniel