Dual colour power LEDs on PCs

Could you not sort this on the current led with diodes? Brian

Nope, it's a 2-pin. LED is driven across the outputs.

Perhaps there's a short to ground on pin 4.

Another thought ...

That red might only be visible in standby/sleep state.

When the board is actually powered off, the LED is naturally devoid of electrons and doesn't light.

I don't think so, because there are only two pins which I expected to be pos and neg in one stage, and neg and pos in the other state ...

That's what I want.

The SBC does actually have a surface mounted two-colour LED, which works as expected, provided the external power brick is connected, I want a case LED to follow what the on-board one does ...

I'll check, but if so I'd expect it would drag the on-board "off" light down to ground and it not work either, but it does work.

TBH I don't see much use in these lights unless the PC is in a noisy environment. I cant tell when power is on & when hdd is accessing.

NT

This is a fanless SBC, with onboard eMMC, which runs off a 12V power brick, so it really is silent ...

eh, it's all your fault for coming up with the one exception :)

I don't think the LEDs will come to any harm if you just stick them on the relevant pins and see what works.

NT

The manual does indeed say each pin has a pull-up resistor, and I would expect it to pull down one pin or the other depending which colour it want to show.

But why would the LED show one colour when on, but _not_ the other colour when off? Given that both colours work, depending on which way round I connect it ...

Maybe the onboard LED you are comparing against (which is not documented in the manual!), is perhaps just showing a 'power connected' confirmation that you have your external power brick attached - it's not actually sleep.

I have equipment here that works like that.

System Power States

Power on - one colour Sleep - other colour Off - no power so no led at all

Avpx

Hmmm, have probed them with a multimeter ...

When the machine is on, the on-board LED is green, pin 2 is at +5V and pin4 is at 0V, so the green external LED shows "on" as expected.

When the machine is asleep (or is shutdown) the on-board LED is amber and both pins 2 and 4 are are at +5V which explains why neither colour of the external LED across them is lit.

I can't see how the external LED can show red for "off" when connected as per the manual. There's no setting in BIOS to let machine know it has a bi-colour LED available.

I'm sure you've got the right LED. Are you sure you're identifying pins 2 & 4 correctly, along the side of the connector rather than across it? I've got that wrong more than once before. Pins 2 & 3 should give the readings you describe in your other post. That is, the second row

The FP PWR_P/SLP_N: Power/Sleep messaging LED terminal 1 with 510? pull-up resistor to +5V_A voltage. Connect it to an extremity of a dual-color power LED for power ON/OF, sleep and message waiting signaling. Please refer to Intel® Front Panel I/O connectivity Design Guide, chapter 2.2.4, for LED functionalities and signal meaning. FP PWR_N/SLP_P: Power/Sleep messaging LED terminal 2 with 510? pull-up resistor to +5V_A voltage. Connect it to the other extremity of the dual-color power LED above mentioned

So it seems you can attach an R+G LED and get: R=off G=on => green: power on R=on G=on => yellow: sleep R=off G=off => dark: off

The description agrees if there is a ground available, so a pin being pulled up high turns the LED on. Though I would have expected an additional wire on the connector for that, and the Intel doc suggests back to back G+Y LEDs. Either way, you'll never get red.

If I pull up the schematic:

S3_LED=low S5_LED=low: machine on, LED=green S3_LED=high S5_LED=low: sleep, LED=yellow S3_LED=low S5_LED=high: soft-off, LED=red S3_LED=high S5_LED=high: hard-off, LED=dark

which implies an R-G LED with separate ground, rather than an Intel back-to-back G-Y LED.

Since it's firmware controlled, using either would be possible (with different results).

Strangely, the on-board LED has a completely different setup that appears to be based on reset and power rail state, rather than software controlled. So its behaviour could well differ.

Theo

I think they're assuming and amber+green LED, that's certainly what's onboard, you can see the individual dies on the LED, and it isn't mixing red plus green to get yellow, whereas I have a red+green LED.

It seems they're using the intel physical connector, but with different meanings for the signals.

Yes despite the doc, that's the conclusion I've come to; use a 3-pin LED, connect the green anode to pin2 and red anode to pin4, and the common cathode to a ground I can borrow from elsewhere (e.g. the HD LED cathode)

then the green side will stay on all the time, the red will turn on when the system is sleeping or shutdown, thereby mixing to give yellow, so I'll get green or yellow, rather than green or red

Poor documentation though ...

I found a 3-pin amber + green LED in the parts box, and yes it works as above, except amber+green is not very distinguishable from green alone, so I'll buy a 3-pin red + green LED

Well depends which way round you're viewing it, but the ones identified in green as per this diagram.

The disk LED, reset and power switches function OK.