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Old 10th August 2010, 11:06 AM   #11
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As phofman has said, pushing the power button momentarily will initiate a controlled shutdown, where the computer closes all open files and saves it's settings.

Pushing the button for ~5 secs forces the PSU off and is normally only used when the PC locks up and refuses to do anything including shut down, this leaves files open and although XP and later systems almost invariably cope with it, it runs the risk of something being corrupted if a write to the hard disk is interrupted. Start-up is protracted anyway due to the disorganised state of the file system if you force the machine off like this and in the worst case a re-install may be required.

Have you checked that you can actually get the machine to start without the keyboard, mouse and monitor? Some PCs may refuse to do so, and although there may be BIOS settings that will allow it, it'd be better to check now than discover later that you have a problem.

w
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Old 11th August 2010, 01:27 AM   #12
wwenze is offline wwenze  Singapore
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No keyboard halts POST by default but it can be circumvented by setting "Halt on" to "No errors" in the first BIOS option page.
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Old 11th August 2010, 07:24 AM   #13
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what powersupply are you using in your pc?

with many of the mini-box powersupplys you have a ACC trigger ,which will shut down the pc after a certain amount of seconds and after a minute or so it cuts power completely.

M3-ATX-HV, intelligent ATX automotive power supply, 12/24V - power your PC in a car

I have been doing tests using a atom pc with a 4gb flash drive. with no monitor attached and 1 gigabyte of ram it only draws 900mA from a 12V powersupply.

The 2A 9V transformer you will use for this can be always on or you can add a lm555 circuit to switch that off also with a relay.

It can from 6V to 34V DC

Not sure what your pc specs are you might use a much smaller one.
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Old 11th August 2010, 08:09 AM   #14
dfidler is offline dfidler  United Kingdom
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Questions:
  • What OS do you want to use?
  • What kind of switch are you using? (SPST, SPDT, DPST, DPDT, momentary?)
  • What are the details on your BIOS (manufacturer, revision)
  • Which motherboard are you using? (manufacturer & model #)
  • Have you looked through your BIOS options for power options, which ones are available?

Note: You should never do a 'force shutdown' on a computer because it increases the risk of losing data and corrupting your file system. In windows, if the system doesn't shutdown nicely, it will boot into the your computer wasn't shutdown properly last time screen which may delay boot times or halt boot completely.

Always opt for the soft shutdown method.

And the method to achieve that depends entirely on the OS and BIOS (manufacturer & version) that you have on the PC.
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Old 11th August 2010, 08:16 AM   #15
dfidler is offline dfidler  United Kingdom
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Actually, it just dawned on me that you're probably trying to mate the computer on/off behavior to the enclosing devices power switch (which is probably SPST).

Try going the other way. Mate the device's on/off behavior to that of the computer. Hook a 12v relay up to one of the power plugs on the computer's PSU that triggers the power to your device. That way, when the computer turns on, it turns on your amp (or whatever).

Then, replace the switch in your chassis from the one in your computer case and wire it to the mobo. Then it's just the software that handles the soft shutdown or suspend to memory features.

Actually, you don't even need one of the PSU plugs; just wire it to the Case Fan or Alt Fan port (also 12v).

Cheers,
Dave.

Last edited by dfidler; 11th August 2010 at 08:18 AM.
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Old 11th August 2010, 08:22 AM   #16
dfidler is offline dfidler  United Kingdom
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PS - You'll never make this completely headless. Neither OS will ever boot perfectly every time. There will be times when you need to hard-reset your system which will require you to interceded with windows.

Similarly, with linux, you will need to set the 'disk check boot interval' setting using tune2fs. Otherwise, your system will automatically do a filesystem check every 20-100 boots (thereby delaying boot time).
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Old 11th August 2010, 08:43 AM   #17
dfidler is offline dfidler  United Kingdom
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Also, I just realized that I'm assuming too much about your amplifier. If it's the kind that turns on when it gets power then the above will work.

However, if it's like my Denon, which has a power switch plus a soft switch, you'll need to design a circuit that generates the momentary press of the power switch to the amp.

I've no idea if this can be achieved with some simple gates, caps, or whatever (probably with some caps to delay the momentary press; shrug) but it can be achieved with a timer circuit and, optionally, an ALU (though it would take me a few months to design the circuit as I really don't remember all that much from the classes where I built the PDP-11 CPU.

Cheers,
Dave.

Last edited by dfidler; 11th August 2010 at 08:45 AM.
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Old 12th August 2010, 08:40 AM   #18
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Quote:
Originally Posted by dfidler View Post
Questions:
  • What OS do you want to use?
  • What kind of switch are you using? (SPST, SPDT, DPST, DPDT, momentary?)
  • What are the details on your BIOS (manufacturer, revision)
  • Which motherboard are you using? (manufacturer & model #)
  • Have you looked through your BIOS options for power options, which ones are available?

Note: You should never do a 'force shutdown' on a computer because it increases the risk of losing data and corrupting your file system. In windows, if the system doesn't shutdown nicely, it will boot into the your computer wasn't shutdown properly last time screen which may delay boot times or halt boot completely.

Always opt for the soft shutdown method.

And the method to achieve that depends entirely on the OS and BIOS (manufacturer & version) that you have on the PC.
And I'm working on a very simple soft shutdown that simply activates the power button for a half second, waits 45 seconds and then activates it again for 5 seconds. I have a whole bunch of Motorola (Freescale) 68HC908JK1 processors from a different project that would do this just fine. Should only take 3 resistors, 3 capacitors and a 2N7000 and a crystal.

G
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Old 12th August 2010, 08:44 AM   #19
phofman is online now phofman  Czech Republic
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Quote:
Originally Posted by stratus46 View Post
And I'm working on a very simple soft shutdown that simply activates the power button for a half second, waits 45 seconds and then activates it again for 5 seconds. I have a whole bunch of Motorola (Freescale) 68HC908JK1 processors from a different project that would do this just fine. Should only take 3 resistors, 3 capacitors and a 2N7000 and a crystal.
G
Why don't you use the PC power button as the primary shutdown button and operate the rest of the chain with a relay hooked to the PC PSU line, e.g. 5V?
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Old 13th August 2010, 08:36 AM   #20
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Quote:
Originally Posted by phofman View Post
Why don't you use the PC power button as the primary shutdown button and operate the rest of the chain with a relay hooked to the PC PSU line, e.g. 5V?
Agreed. How do you make the power button (relay) activate for 1/2 second and then deal with the possibility of some software hanging and preventing the actual shutdown?

G
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