I'm building a simple circuit to drive an LED status indicator in a project built around a RPi. The circuit takes its power from the same source as the RPi and is connected to one of the RPi GPIO pins. The aim is that the LED should start blinking when the system is powered on and continue to blink until the RPi system has finished booting, at which a process is launched to set the GPIO high, causing the LED to stop blinking and stay latched on.
I started with this circuit
Which I modified like so:
I've implemented a few circuits as designed by other people but this is the first I've attempted to design myself (ok, only a tiny part is mine, but hey). It does seem to work but I'm not confident that it is robust and I would appreciate any advice on how to do it better, or more simply.
One thing I've noticed when setting up on a breadboard is that if I just hold the wire that goes to the GPIO pin between my fingers - without attaching it - the LED latches on. I don't understand why. I'm not planning to put the circuit somewhere people can stick their fingers in but I would like to understand why it does this and if it is a symptom of a design flaw.