* Multi-board system: power supply, amplifier, and I/O board
* Demonstrates inter-module wiring

.subckt power_supply VCC GND
J1 AC_IN AC_GND AC_INLET
.ends power_supply

.subckt amplifier VIN GND VOUT
R1 VIN N001 10k
C1 N001 GND 100n
J1 VIN GND INPUT_CONN
TP1 VOUT
.ends amplifier

.subckt io_board SIG_IN SIG_OUT GND CTRL
J1 SIG_IN SIG_OUT DB9_CONN
J2 CTRL GND CTRL_CONN
.ends io_board

* Top-level instantiation
X1 VCC GND power_supply
X2 VCC GND AUDIO_OUT amplifier
X3 AUDIO_OUT CTRL_SIG GND ENABLE io_board

* Top-level connectors
J_CHASSIS GND EARTH chassis_gnd
TP_VCC VCC