Transmitter
The top part of the transmitter circuit is the power control of the transmitter. By writing PA0 low you can turn the chip on, the user can also choose to simply ground the base of the transistor if they want the system on the 100% of the time.
PA1 is coded to a timer that makes +5V, 40kHz pulses. that signal is split and sent to an inverter and bypassed. The original and inverted signal are sent to the chip and boosted to +8V and -8V still at 40kHz. these signals are connected to both sides of the transducer.
Pins 2 and 6 on the MAX232 chip are used to generate +8V DC and -8V DC. Those sources are used to power the receiver and extend its voltage range.
Timer 2 Pulses
Original Signal
Inverted Signal
Due to an inaccuracy with the Delay_100us(); function 9 pulses are generated.
Sources
+8V Signal
+5V Signal
-8V* Signal
The -8V signal only went to -5V for some reason
Zoomed in Sources
+8V Signal
+5V Signal
-8V* Signal
The -8V signal only went to -5V for some reason