[mythtv-users] Power Relay for Frontends

Gary Dawes gary.dawes at gmail.com
Sun Oct 21 06:48:56 UTC 2012


On 21 October 2012 07:28, tortise <tortise at paradise.net.nz> wrote:

> On 21/10/2012 3:42 a.m., DaWorm wrote:
>
>> Measure the current draw to your TV both when active and when off.  When
>> you turn the TV off, you can detect the decrease in current and initiate
>> shutdown on the frontent
>>
>
> I am not sure what advantage measuring drawn current offers over a USB
> rail that is either 5V or 0V?  Sounds like a lot of extra electronic
> wizardary / complexity to achieve the same input control?  (I agree it
> would be helpful when the monitor has no switched USB out.)
>
>
> > (oneshot to opto that shorts power switch
> > pins).
>
> Touching the power switch momentarily, seemingly the equivalent, on my
> frontend does nothing. If it did tell the FE to gracefully shut down then
> another relay could probably be wired to achieve this.
>
> While not all monitors / TV's give EDID responses, sensing the presence of
> the monitor via EDID (or somehow sensing the voltage on the USB bus?) via a
> cron job to gracefully turn off seems to me a good idea.
>
> I need to read up on serial ports, however it may be a serial port can be
> recruited to sense the TV's 5V and use that in conjunction with CRON to
> cover all turn off cases (for USB switching monitors).  In that event the
> cron job would sense for 0V and when it got 0V that would trigger a
> graceful shutdown.
>
> There may be an even more KISS elegant way than this to achieve a graceful
> power off?
>
>
> >Same for power on, the increase in current also triggers the
> > oneshot.
>
> My proposed cheap set of relay and diodes in conjunction with the FE Bios
> achieves power on via the TV power remote.
>
>
> >The circuit itself wouldn't draw much power but would have to
> > be on all the time.
>
> Certainly that in itself would be compatible, however the relay idea draws
> no power when off.  Only the TV standby power is then drawn.
>
> I gave some thought to using a Raspberry Pi to do similar but that also
> seems to duck the KISS principle...
>
> Measuring power use from these power supplies and also what is actually
> charged is complex and difficult to measure, because where the current is
> out of phase with the voltage (that is the case with the switch mode power
> supplies that are generally utilised in these fancy digital kit) measuring
> real power charged is not at all straight forward.  The cheap power meters
> available are likely to under estimate the true position.
>
> The other scenario example I have is a Revo with a monitor and separate
> Amplifier connected. In that case the power to the monitor and amplifier
> could be even more simply controlled using a 5V Relay connected to the
> Revo's USB bus, that when the REVO is powered up it turns on the amplifier
> and monitor's mains power, and when the FE is turned off it also
> automatically turns them right off.  Can still do remote WOL of the REVO in
> that configuration.  Not the same as a monitor with an IR remote that was
> first described.
>
>
> In the vein of KISS, a couple of suggestions:

In the UK you can get TV standby killers, which have an IR receiver to
learn the TV off command, and then shuts off the power. These are available
in multi-gang or single-gang form and readily available via the likes of
Amazon and ebay. I have used these with diskless frontends and AV equipment
such as DVD & receivers successfully. these also turn the power back on
when the TV is turned back on

The other thing I have done in the past is to teach LIRC the TV off
command, and tie it to the shutdown command on the frontend.

Gaz
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