The Pulse Sensor from https://pulsesensor.com re-designed to be made on a tiny flex PCB to replace the HR sensor of the SMA-Q2 watch. Have the board manufactured via the OSHpark flex sevice. This way the board remains as low profile as possible. As a light shield to avoid light hitting the ADPS-9008 from the sides I used a piece of the black component tape the SC70-5 style opamp came packaged in. Just had to cafully cut out the bottom of the tiny tray et voila! This is usable for PPG acquisition from the wrist, although the peaks are less pronounced than on the fingertips. I ended up using higher value current limiting resistors for the LEDs, something around 1.2 kohm seemed more reasonable since otherwise the sensor was overwhelmed. This also limits the overall current consumption of the sensor to about 1mA. The LED current limiting resistor value probably also depends on skin color.
Note: the board version depicted on the photos is an older revision where I placed the wire pads wrong.