Led on/of

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This is too easy to think about, but it helped me, so here’s my ‘tutorial’

I have very small led (used in model-train hobby projects), that I want to have switched on when a device somewhere in the house is switched on by a rule or condition. Of course I can check the pimatic-page, but I want to see this without taking out my phone/table or whatever.

So. The ground (shorter pin) of this LED is on the ground pin (6th pin of my GPIO pins and the power pin (the longer one) is on pin 26, which is GPIO 7
(I did not use a resistor for this led, is looks like it’s not needed, but correct me if i’m wrong with that)

Next I created a new device with class GpioSwitch and have 7 as GPIO pin.

This device van be used as any other device in Pimatic, you can switch it on manually or have it switched on, for example when a specific temperature switches on a socket for example.

See, too easy to think about…

Very fine tutorial, but as many will try this i ahve to correct you on the part with the omitted resitor. You should never drive a LED directly from a digital output. The reason is quite simple: The resistance of an LED is (theoretically) 0, so applying ohm’s law U=R*I you would get an infinite current.
Of course this is not possible, but the LED will consume the GPIOs maximum current.
This might work some time, but in worst case you will destroy your raspberry with that. You might also destroy the LED or even worse you shift the whole raspberry’s voltage levels getting a weird behaviour on other pins.

So please add a simple resitor to your circuit. Simple rule here:
Higher Resitor -> lower current -> less light from LED.