How to make a laptop start up when ext power is applied?

Hardware dependent.

If the system has a BIOS setting that controls the power settings - it can be done. If it does not - it cannot be done.

Leave them on all night, or BIOS setting, or come around and switch on in the morning - that's how the showrooms do it. If no BIOS setting is available - often the case on laptops - then you need to build a little circuit that pulses the power control line when the standby voltage appears. I've done this many times when repurposing laptops to use as the core of an embedded system. I used an 8-pin PIC because I had them lying around. A 555 would do just as well.

larwe wrote

Very interesting - would you be able to post more details?

It's highly platform-specific, but here is the general principle:

When power is available, there will be a standby voltage present somewhere on the board at all times, to support Wake-on-LAN, wake-on- Bluetooth, etc. On a desktop PC, there is an explicit +5Vsby output from the PSU. On a laptop, you either get lucky with the silk- screening or you probe around the board with the machine switched off. Start with the Vcc pin of any small microcontroller you can observe. The line should also be available at any internal PCI, PCIe slot, I believe.

IIRC when I had an Eee 2G Surf, it provided USB bus power at all times when AC was present (to hell with the spec, full speed ahead, right?). So that might be a convenient takeoff point if you have no luck elsewhere - it won't be available when the unit is running off battery, though.

The power button on a laptop is typically an active low input to some kind of power management microcontroller. Pull it low, the machine starts up. Unfortunately in most cases it is not enough to simply tie that line low because holding the button low typically invokes an emergency hard shutdown in the case where the main CPU is irrevocably crashed.

So get your 8-pin PIC, or your 555 rigged as a one-shot. Configure it so that as soon as power is applied, it will wait (say) 1 sec for everything to stabilize, then pull the power-on line low for 500ms, then release that line and go to sleep forever. Power the micro/555 from the standby voltage and connect the output to the power control pin.

An RC might sometimes do the trick too, but I haven't found this to be very reliable in the past (too iffy, especially if there is a brownout or power glitch that leaves the PSU in its switched-off state, but the RC charged above the Vil voltage of that control line).

Inaccurate. You forget that this message was cross-posted to comp.arch.embedded, where we don't need operating systems nor user manuals, and any signal that can be physically accessed can be used, even if it isn't brought out to a LED or pushbutton.

Actually I just re-read your post and I realize I may have misinterpreted your skillset (based on the fact that I came across the message in c.a.e I assumed you were an embedded person).

If you need actual design/building help, email me - the address is valid.

No - I did not forget - I ignored and followed up on exactly what had been given.

Without modification of the hardware, which a "computer showroom" mentioned in the beginning of this posting would not do unless they did not want to sell those particular laptops again, what I said is accurate.

It is *hardware dependent*. If the system has a BIOS setting that controls the power settings - it can be done. If it does not - it cannot be done.

Now - if the OP is intending to modify the hardware - well sure, it could be done. Then again - why mention a 'computer showroom' if that is so - after all, I have not seen a computer showroom that modified their systems (especially laptops) in order to turn them on. They either left them on or they had someone who worked there turn them on when the store opened.

It's not clear that a computer show room was the intended application. I read it as the poster suggesting a situation where people might already be doing something similar to what was needed for unspecified application.

In a computer showroom, wake-on-lan might be a possibility. Just have an pre-ATX box wired to the light switch that continually hits all the machines with whatever traffic will wake them up.

Realistically though, I bet they leave them on all night - even in the unlikely case that its store policy to shut them down, I bet they usually get left on.

wetware. A minimum wage worker walks by and hits the power buttons on all of them.

More likely, they're simply left on 24x7.

That sounds like it's BIOS-dependant rather than hardware-dependant. And BIOS is software, not hardware. ;)

To be more accurate, the BIOS is "Firmware*, which makes it more hardware-dependent than not.

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it more

A hardware engineer won't generally make that distinction - to such a person, chips are hardware and the bits stored within them are software.

So, how many angels can dance on the head of a pin, anyway?

larwe wrote

I am quite experienced hardware/software developer, ex 8048, 8051, z80, z180, z280, 80x86, H8/300, but don't like to dismantle laptops because getting them back together again can be tricky ;)

Also I know very little about PC architecture - beyond constructing loads of PCs from standard parts.

The application in this case is indeed an embedded comms controller, interfacing to a satellite phone and outputting some data on the VGA output.

Thank you for posting the other stuff - very useful.

I did it on a real PC with a capacitor across the startup button....... no reason it shouldn't work for a laptop...

It's not always reliable - see other post.

Good, I guessed right the first time then :)

The Eee is very simple though, not challenging to disassemble at all. Lots of people are using them for robotics and other applications. It's a very cheap SBC for the performance, especially the older/ smaller models which can now be found on eBay under $120 sometimes.

Enjoy :)

Peter - check the bios for power-on options, ie what happens when power is turned on. Usually there is a message on the screen when the computer is first booting that says, roughly, "press xxx for setup".

Hul

I don't know, but if was up to me, I'd put them on a wired network, leave the power on, and send them wake-on-lan packets when I wanted them to start.

Clifford Heath

If I were in that situation, I would use the RTC and BIOS turn on time setting. No hardware mods required. This has been a standard feature of PC BIOS setup programs for a very long time. Of course if you need anything more flexible you will need to use the ideas provided by the other posters.

As an example, I checked my old NEC Versa VXi and it has this capability in the Power Management Setup screen.