Resistance to Power Supply !PS_ON pin

I soldered up my v1.2 Motherboard with the ATX header. I plugged in the power supply, flipped the switch, and nothing happened. Long story short, it appears that 10K is too much resistance between ground and !PS_ON. If I jumper over R18 (10K), then the switch works and the power supply turns on.

Did I do something wrong? Is my power supply "special"? Or have others experienced this as well?

Edited 1 time(s). Last edit at 03/06/2010 12:28PM by buzzard192.

you're supposed to have no resistance there at all. On my setup, I feed that pin directly into my arduino, and set output to zero when I want it to switch on. If you're determined to have resistance in there for some reason, make sure it's less than about (0.5v/1mA=~) 470 ohms.

That line is an *input* to the power supply that's internally pulled up to 5vsb via a resistor or current source or something- don't assume which. you need to pull it below 0.7v or so for the ps to switch on.

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Wooden Mendel
Teacup Firmware

it depends on the power supply. some just need a jumper, and some will only activate under load.

check out [pinouts.ru] or [pinouts.ru]

if the psu fan comes on with just a jumper then you do not need the resistor. most of what I have seen is 10 Ohm 10 Watt.

Edited 1 time(s). Last edit at 02/06/2010 06:35PM by mfsamuel.

the resistor is to load the 5v rail so 12v stays fairly regulated, the PS_ON signal is separate. you need both.

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Wooden Mendel
Teacup Firmware

Surely the enable pin of the PSU should be driven with an open collector/drain drive. I suspect the series resistor was an attempt to fix the Arduino dragging down the enable when it is not powered itself.

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[www.hydraraptor.blogspot.com]

yes it should be driven with open drain.

I simulate an open drain by setting the pin to zero then toggling input or output as necessary.

My arduino runs from the 5vsb line of the same power supply, so the issue you mention doesn't exist here.

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Wooden Mendel
Teacup Firmware

I do the same thing. I output 0 to turn the PS on and set the pin to input to turn the PS off. I don't have the Arduino powered by the PS standby so if I unplug the USB cable or the computer's power cord, the power supply turns on, which kind of sucks.

When I put a volt meter on the green wire, it reads 1.5 V, I think. So outputting a digital 1 (5 V) wouldn't be very nice.

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Darwin clone, Gen 2 electronics, Arduino Duemilanove w/ AtMega328, 5D Firmware, Pinchwheel extruder
[www.codeerrors.com]