Hit the power button (jumper) on another PC ?

I'm part way through building my design for something that sounds very similar.  I'll be using a Pi to drive it and will have relays to switch mains power, the power button and the reset button. I'll also have detection of the power led being on, along with serial console for each attached PC.

I couldn't find an off the shelf device that did all of this in one box, and being able to remotely physically push the power button, hold it down for four seconds etc. is a huge plus point and I'm surprised that there don't appear to be remote power strips that provide this sort of thing.

You will want relays for the power/reset switches as you can't be sure how the motherboard implements these. You run the risk that the motherboard applies 5V to your Pi's 3.3v-only gpio pins, or takes too much current if you don't use a relay.

If you get a decent network card (intel 1G pci-e ones work for me) then WOL normally works. I can physically disconnect power, reconnect it and have WOL work fine.

Sometimes with a shutdown it'll depend on the OS and/or driver what happens, for some cards and linux distros I've had to use "ethtool -s eth0 wol g" very late in the shutdown sequence to enable MagicPacket WOL to work. Various windows drivers I've seen have an option to enable WOL that defaults to off etc. Finally, you may need bios settings to be correct for it to work.

tuna salad wrote:

 

For example, if you do a shutdown, the motherboard won't boot the system on a power cycle. 

there's normally a bios option for that (but not always especially if it's a desktop board), it's usually called something like 'power state after power failure' and has options like 'always on', 'always off', 'previous state'.  If yours is set to always off or previous state then what you're seeing is to be expected.

selsinork wrote:

 

I'm part way through building my design for something that sounds very similar.  I'll be using a Pi to drive it and will have relays to switch mains power, the power button and the reset button. I'll also have detection of the power led being on, along with serial console for each attached PC.

 

I couldn't find an off the shelf device that did all of this in one box, and being able to remotely physically push the power button, hold it down for four seconds etc. is a huge plus point and I'm surprised that there don't appear to be remote power strips that provide this sort of thing.

 

You will want relays for the power/reset switches as you can't be sure how the motherboard implements these. You run the risk that the motherboard applies 5V to your Pi's 3.3v-only gpio pins, or takes too much current if you don't use a relay.

Yes, that's the other reason to use a relay -- you don't have to worry about the motherboard's implementation.  Also, I think the relay sovles potential grounding issues.  I was thinking I'm not sure how to ground the pi with the PC -- if I power it off of the PC, it may not get juice at some PC power states.

Can you point me to a collection of hardware that you think would work?  I don't know how to connect that relay board to the pi and what software interface I should use.

If you get a decent network card (intel 1G pci-e ones work for me) then WOL normally works. I can physically disconnect power, reconnect it and have WOL work fine.

Sometimes with a shutdown it'll depend on the OS and/or driver what happens, for some cards and linux distros I've had to use "ethtool -s eth0 wol g" very late in the shutdown sequence to enable MagicPacket WOL to work. Various windows drivers I've seen have an option to enable WOL that defaults to off etc. Finally, you may need bios settings to be correct for it to work.

I'll be messing with this.  One problem is that I don't have any free pci slots on that machine, so I can't add an intel nic.  I haven't ruled out using the crappy onboard NIC for WOL.  I just haven't gotten it to work yet.  Another option is USB NICs.  Some support WOL.

there's normally a bios option for that (but not always especially if it's a desktop board), it's usually called something like 'power state after power failure' and has options like 'always on', 'always off', 'previous state'.  If yours is set to always off or previous state then what you're seeing is to be expected.

Yeah, that attribute only had two options, and even when it's 'on,' it doesn't always work.  I don't think there was an 'always on' option.  One time, I did a 'shutdown' and it wouldn't boot on power cycle.  One time, I updated the kernel, and it wouldn't boot on power cycle.  It's meant to be a desktop board, not a server board, so those options aren't very robust.

In any case, a machine that remotely hits the power button would be awesome.

tuna salad wrote:

 

if I power it off of the PC, it may not get juice at some PC power states.

you could power it from 5VSB - pin 9 on the ATX power connector http://en.wikipedia.org/wiki/Atx#Power_supply as this will have power as long as the PSU is connected to the mains.  However keep in mind that 5VSB likely has limited power available, check the rating on your PSU before doing this.

Can you point me to a collection of hardware that you think would work?  I don't know how to connect that relay board to the pi and what software interface I should use.

Not particularly, sorry. I'm building mine from the ground up, designing the pcb's myself.

I'm using an MCP23017 I2C gpio expander and interfacing everything to that. You can connect up to eight of these to a single I2C bus meaning that I can easily expand the number of channels. The software interface is just the kernels standard GPIO interface under /sys/class/gpio, nothing special or specific to the Pi, but there's nothing that needs high speed or out of the ordinary features here.

   Another option is USB NICs.  Some support WOL.

Usually a different 'usb wake' option in the bios for that.

In any case, a machine that remotely hits the power button would be awesome.

I remember finding a blog post some years ago where someone had a machine that kept locking up and had arranged another PC to be facing it in the computer room. Some careful alignment and something glued to the front of the CD drawer on the second system allowed him to eject the CD tray and have it press the reset button on the first PC. Quite ingenious

There's always this, which seems to do exactly what i want:  http://www.skpang.co.uk/blog/archives/753

or maybe this:  http://arduino.cc/forum/index.php/topic,24161.0.html

tuna salad wrote:

 

or maybe this:  http://arduino.cc/forum/index.php/topic,24161.0.html

this r2duino runs runs on 5v, so i can't power it off the raspberry pi

tuna salad wrote:

 

There's always this, which seems to do exactly what i want:  http://www.skpang.co.uk/blog/archives/753

and that's surprisingly similar to what I'm doing, 4 relays like that for mains, then 8 much smaller reed relays for each of power and reset buttons for four channels. My mcp23017 has 16 gpios compared to the 8 on their 23008, I use the remaining four to read the state of the power leds.

Really don't understand what the fascination with darlington arrays is though..

tuna salad wrote:

this r2duino runs runs on 5v, so i can't power it off the raspberry pi

Yes you can, it's a usb device. You just plug it into the USB port on the Pi.

It's another level of abstraction though, you'd basically be using the Pi to download code to the arduino and having the arduino push the buttons. So you'd need to work out how to communicate from the Pi to the code you write for the Arduino so that you can tell it what to do.  The skpang relay board is probably easier to get started with if you don't have arduino knowledge already.

Also be aware that the 'relays' on that board are solid-state, not mechanical. Nothing necessarily wrong with that, just something to consider.

so, this looks like the absolute easiest solution: http://beaglebone.cameon.net/home/devantech-2-channel-usb-relay

unfortunately, it's out of stock.

so piface looks perfect.  i didn't know that even existed.  so i bought one from newark.  i'll let you know how that turns out.