The BIOS on your computer’s motherboard will typically allow you to wake up your computer without additional hardware. More or less any modern machine should have a function for time-controlled booting. There are two methods that can be used with MythTV to wakeup your computer.
This uses the system's ACPI subsystem and requires the presence of /proc/acpi/alarm or /sys/class/rtc/rtc0/wakealarm.
This is a small program that reads and writes the WakeUp time in the BIOS. This is done via /dev/nvram on recent kernels (>2.4.6, including 2.6.x) or, alternatively, via direct ISA access. On this WakeUp time the computer is powered on automatically.