I didn't see the picture. According to your description, pin 3 is the output of 555, so it can't be directly connected to the power supply. It must pass through the load, and the maximum load current is 200 mA. No more than this. This pin can output in both directions, and the phase should be clear when using it. In addition, the flip trigger voltage of 555 is 1/3 and the power supply voltage of 2/3 is taken as the trigger threshold. If it is used for oscillation, the power supply has little influence. If it is used as signal detection, it is necessary to amplify and shape the external signal and cooperate with the internal signal, otherwise it is easy to fail.