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Powering on your cab without hitting the power button: the cap trick

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ac3:

Thanks Peale, great guide.  :applaud:

Zebidee:

Long ago I copied Peale's cap trick page into my mamedocs folder, which is full of heaps of interesting bits and pieces relating to arcade cabs & emulation. You can use this trick (or variants on it) for all kinds of electronic gear, form TVs to PCs to audio amplifiers.  It is just too good an idea.


RandyT:

I'm as little confused about this one.  I understand how it works, but how is this better than simply jumping the "power on" (green) line with an adjacent ground line on the ATX power supply?

What am I missing? :)

RandyT



*edit* "Power On", NOT the "Power Good" line as mistakenly stated earlier.  "Power Good" is set to 5v as a way for the power supply to let the PC know that the supply is stable and ready to supply power (if anyone cares ;) )

Zebidee:


--- Quote from: RandyT on December 10, 2008, 04:05:38 am ---
I'm as little confused about this one.  I understand how it works, but how is this better than simply jumping the "power good" line with an adjacent ground line on the ATX power supply?

What am I missing? :)

--- End quote ---

Firstly, the cap trick allows a pulsed signal to be sent, which simply shorting wires won't do.  Some devices require a pulsed, changing state to be detected in order to power up.  The cap trick allows a closed.shorted circuit, but then opens the circuit once the capacitor is powered up.  More than 'jamming' a button, it simulates pressing and releasing a button.

You might not need this for an ATX power supply, but older PCs need it and certainly TVs and amps need it quite often

RandyT:


--- Quote from: Zebidee on December 10, 2008, 05:59:09 am ---Firstly, the cap trick allows a pulsed signal to be sent, which simply shorting wires won't do.  Some devices require a pulsed, changing state to be detected in order to power up.  The cap trick allows a closed.shorted circuit, but then opens the circuit once the capacitor is powered up.  More than 'jamming' a button, it simulates pressing and releasing a button.

You might not need this for an ATX power supply, but older PCs need it and certainly TVs and amps need it quite often

--- End quote ---

Yeah, I get that ;)

But as it is presented in the context of an ATX supply, it seems to be overkill and that is what was confounding me.  I haven't seen a PC with an ATX supply where simply grounding the "power on" (green) line on the supply has created an issue.  In fact, it's the only way one can use an ATX supply for anything other than a PC.  Most of the older Pre-ATX PCs just used physical on/off type switches (not momentary type) so this wasn't really an issue there either.

But for monitors and amps with soft power (and which don't have the ability remember the last state) I can see this as useful.  Perhaps the context should be altered?  Yes, it will work for an ATX box, but it's probably just extra work with little to no extra benefit for the trouble, IMHO.

RandyT

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