Yes, I had thought that might be the case. I thought of using a Grey code disk with opto-sensors but I was looking for a way to simplify things.
The alternative is to place the sensor on the rotating vane shaft and use the earth's magnetic field. But that requires having some electrical coupling to the device, either by wires (not practical) or a wireless connection via ESP8266, ESP32 or 24L01 (again not too practical since it will require batteries etc.).
By the way, I have answered my own previous question thanks to Google! The chip is the HSCDTD008A.
Oh well. Let's see if I can get the chip working using the datasheet info anyway.
Thanks for your input.