Switch off HdmiPi display with software?


12 posts
by Sjefke » Sun Jan 11, 2015 4:23 pm
The HdmiPi display is pretty good. I use it for signage. http://hdmipi.com/
Is it possible to switch the display off with a python script?

Of course, this command will work:
/opt/vc/bin/tvservice -o
But then the screen turns blue. That is not what I want.

HdmiPi has a little on/off switch at the back. After switching the display off, the Raspberry is still on. That is good.
I want to switch the display off on a specific time, and also with a PIR sensor.

If there is no software interface available, maybe it is possible that the display when searching for input is black instead of blue?
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by alexeames » Sun Jan 11, 2015 7:04 pm
Hi,

You are now I think the third or fourth person to ask about this feature. The way things are now, this cannot be done programmatically.

I am going to have a go at hacking the power switch to use a GPIO pin to toggle the screen instead of/as well as the power switch. I'm not sure yet how easy this will be to implement (don't know if it's a 3V3, 5V or 12V circuit) because I haven't looked yet. Pressing the power button shorts to GND (I think - still to check), so even if it was higher voltage than the Pi's 3V3, something like a Darlington array chip or transistor could be used here.

So in summary, with HDMIPi as it is, I'm pretty sure it can be made to work, but will require a little hardware hack as well as some (very simple) GPIO programming on the Pi.
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by Sjefke » Sun Jan 11, 2015 7:36 pm
Thank you for these pointers, Alex.
I will examine this.
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by KenT » Sun Jan 11, 2015 8:22 pm
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by alexeames » Sun Jan 11, 2015 11:12 pm


This is worth a look, thanks Ken, but I doubt it will switch off the HDMIPi backlight.

Will try it though.
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by alexeames » Mon Jan 12, 2015 1:10 pm
Just done some multimeter probing and it appears that this button is on a 3V3 circuit, which means that it should be possible to control it directly with a Pi GPIO port without the need for a transistor. I will stick a resistor in series though to protect the port.

A momentary shorting of the button to GND toggles the screen on/off.

Next step is to hack the board and try it out for real. :D
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by alexeames » Tue Jan 13, 2015 8:58 am
OK. I've got this working now. Will be blogging about it in a day or two.

The good news is that it's quite easy. :D
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by alexeames » Wed Jan 14, 2015 2:24 pm
OK full instructions how to programmatically control the on/off functions of your HDMIPi (wiring, photos, video and Python code) are now published at...

http://raspi.tv/2015/hacking-hdmipi-power-switch

Also a little YouTube demo video
http://youtu.be/qECVrxWmbm0

There will be a part 2 as well :)
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by Sjefke » Sat Jan 17, 2015 9:28 am
This is terrific, Alex. A perfect answer. Thanks!

My "solution" was a very lazy one. The web page was only black during the day and was active in the evening.
However, there is too much backlight bleeding.

Code: Select all
<body style="background-color:black">
<?php
date_default_timezone_set('Europe/Amsterdam');
//  Switch on the display between 17.00 and 22.00 (5 and 10 pm).
$show = date('H', time());
if ($show > 21 || $show < 17)
   die;


bleed backlight.jpg
bleed backlight.jpg (6.76 KiB) Viewed 1551 times

leftside.jpg
leftside.jpg (22.58 KiB) Viewed 1551 times

front.jpg
front.jpg (31.95 KiB) Viewed 1551 times
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by Sjefke » Sun Jan 18, 2015 6:57 pm
Soldering a jumper wire to the power button of the HdmiPi display is very simple.
Now I can really switch off the screen, while the Raspberry Pi continues to work.

The system normally needs 13 Watt (display + Raspberry Pi B version 1 + some sensors). When the display is off, the power is just 7 Watt.
Obviously, with a Raspberry Pi A+ the power demand will be a little bit lower.
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by alexeames » Wed Jan 21, 2015 9:47 pm
How are you measuring the power usage? At the wall socket?

HDMIPi uses only 5 Watts when the backlight is on and the model B uses 2-3.

Have you got some greedy sensors?
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by Sjefke » Tue Jan 27, 2015 10:21 pm
That is a big difference.
I measure with a Brennenstuhl wall socket power meter. Even without the sensors it uses 13 Watt.
Maybe the 12 Volt adapter consumes some Watts?
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