[mythtv-users] Power Relay for Frontends

[Joseph Fry]

> 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?
>>
>
> Additionally I've not tried the CEC pulse 8 device yet as not yet upgraded
> to CEC capable mythtv version, however it may be that using CEC and the TV
> remote a power off menu selection on mythtv might be made to turn off both
> the PC (in the usual way) and additionally send an HDMI (CEC) signal back
> to the TV to also turn the TV off?
>

All you need to do to have turning off the TV power down the frontend is
have it short the power switch pins briefly when the tv turns off.  You can
then set the frontend to shutdown when the power button is pressed... but I
suspect that this would be difficult to achieve in a circuit.

What I would probably do is set a cron job to do a EDID query, and if it
gets no response then I can assume the TV is off and shutdown.
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