[mythtv-users] Power Relay for Frontends

[tortise]

Hi Guys

I attach (I hope) a circuit I've been thinking about for awhile drawn in 
dia format and pdf. (Be gentle on me here, its first time use of Dia)

Basic problem is a good fast frontend computer draws power even when 
switched off, as does a TV.

In the days of CRT the TV could turn off and on with no issue like a 
monitor however with the swanky TV's these days (with USB outs) that run 
their own PC's and (I assume) are better to turn them self off, rather 
than simply having the plug pulled it seems to me the TV may be the 
better device to leave on and disconnect the FE when its not being used.

The circuit sets out a simple idea that seems to me would work. When the 
TV is switched on it turns the relay on, giving power to the FE. If the 
FE is in power on / turn on mode then it would also start. The +5V from 
the PC would then hold the PC mains relay / supply on until both the FE 
and TV had turned off.

Turning ON:
Turning on is done by turning on the TV with the remote.

The mythtv FE can start automagically via BIOS setting or can be turned 
on manually some other way.

Turning OFF:
Select power off on the Myth menu which shuts down the PC ready for full 
power off.  Turn off the TV turns off the PC relay as both relay power 
sources have now gone.

It would be nice to turn this two step power off operation into one but 
I can't see how to simply do that, i.e. have turning off the TV trigger 
turning off the Frontend as well. I suppose one way might be similar to 
a UPS triggering a PC to turn off, in this case the circuitry could be 
modified to send that an off trigger but I don't know the technical 
options / requirements to do that.  No doubt someone here will?

While its usual to have a diode across the relay coil the two diodes may 
well cover this.

Anyone any thoughts?
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