I tried powering the Arduino Nano BLE 33 with a 9V battery and hooked up the Sparkfun Pulse oximeter https://www.sparkfun.com/products/15219
The sensor is constantly blinking unlike when connected to a USB where the LED is constantly on when the finger is on the sensor. The input voltage is the same for the 2 cases. Any suggestions on why the sensor is blinking instead of being constant when the finger is placed ? Thanks