External power-up indicator light, somehow?

yannseznec

I am working on a few projects with the Gem (and some older Bela boards). I very often want to have a power switch on the enclosure. I also generally want to have some sort of LED that indicates that the power has been switched on.
In the past I have done this using the digital output pins, making a thing in my Pure Data patch that turns on that LED when the patch loads. This has the advantage of indicating not only that the Bela is powered on, but also that the patch is loaded and ready to make sound.
The disadvantage of this approach is that it takes some time for the Bela to boot and eventually load the patch. That means that I power on the board but have no indication that the board is powered until 20 seconds or so after I turn it on. That can feel kind of unsatisfying, of course.
I'm wondering if there's a good way to have an external LED that turns on the moment the board receives power?

The next stage, and my ideal outcome, would be to have an indicator LED with two states - like a startup state followed by a "ready" state. Perhaps flashing for startup, and solid for ready. Or potentially use an RGB LED and have two colours, I suppose.

In any case, I'm wondering if anyone has suggestions how to do this? Or is this even already built-in somehow that I'm unaware of?

giuliomoro

That the board is powered on is signalled by the +3.3V line, which is available on the headers.

The Bela running LED's (the one that blinks blue when the project is running) are also available on the headers. These are bicolor LEDs, they would turn red when an underrun occurs.

BelaMini:
P1.02 blue LED
P1.04 red LED

Bela cape Rev C:
P8.34 and P8.38 (not sure which is red which is blue)

Gem:
P2.02 and P2.04 (not sure which is red which is blue)

Additionally, Gem has a second "status" LED, which goes solid blue as soon as the board is powered (at the same time as +3.3V goes high), then it starts blinking when Linux has booted. The signal for this is available on P2.08 .
You can even change its behaviour at some later stage, for instance set it always off when the IDE is up and running.

All of the above signals are already present on the headers and won't take up one of the Bela digital outputs.

yannseznec

ok excellent, some good options to explore there. thanks!