The indicator shows eight wind directions by means of LEDs. The sensors are reed contacts powered by a permanent magnet. The mechanical construction must be such that it is impossible for more than one reed contact to be closed at any one time.
At the instant a reed contact closes, a leading edge is applied to the clock inputs of D-bistables (flip-flops) IC2 and via an OR gate in IC1. This results in the outputs of the bistables assuming the status of the D inputs so that only the LED associated with the closed reed contact lights.
If the wind changes direction slightly, and the reed contact opens, then, owing to the bistable construction, the LED will continue to light. Only when the wind has changed direction so much that another reed con-tact closes will a different LED light.
When the supply voltage is switched on (S1), only D9 will light owing to the power-on reset via R10 and C3. Only when one of the reed contacts has caused a leading transition (edge) at the clock inputs will one of the direction LEDs (D1–D8) light.
The indicator needs to be supplied by a regulated 5 V source. It draws a current of not more than 10 mA.
The LEDs are low-current Siemens types.