Originally Posted by JeffDM
It's not that hard to make circuits wake from standby at a predetermined time. I think I did it with a microcontroller that costs pennies in volume.
Indeed. The PVR that I use has a main board (with the TV tuners, HDD interface, main processor etc.), and a "front panel board", which has a microcontroller and timer. When you put it into standby, the main board sends the time of the next programmed recording to the front panel board, and the main board is turned off. At the alloted time (allowing for the time taken for the HDD to spin up), the front panel board turns the main board on.
Surely this (or something very similar) is how VCRs of old worked? In fact, most of the VCRs I've used in the past required
to be turned to standby in order for the timer to work.
I think the thing with the TIVO is that it's probably got some kind of program delivery control that requires the tuners to be running permanently, in order to receive any updates to the broadcast schedule. There's still room to reduce power consumption though, by running the processor in a reduced power mode, spinning down the HDD, turning off any video processing and output chips etc.