Received PPG from My Supervisor

Dear All,

Actually today i'm not feeling well, it have been 2 days of dizziness and i don't have mood to have my lunch and dinner. Well, that's life. I met my supervisor this afternoon at 2.30 pm because he asked me to take the PPG devices. Before handover to me the PPG, we discuss a bit about the PPG and circuit need to be constructed.

Inside the PPG there are LED DC Current Source and Photodetector, while the end of its is 9 pin "D" connector of male. The brand of the PPG is NELCO oximeter finger probe. Sir Saiful Yusri which is my supervisor explained to me about the functions of the connecter pin which is as table below:-

Connector End Pin	Pin Name	Description
9	Phototransistor cathode	Green wire
5	Phototransistor anode	White wire, phototransistor detects level of IR and/or red light transmitter through the finger
2	LED1	Red wire, anode of the IR LED, cathode of the red LED
3	LED2	Black wire, cathode of the IR Led, anode of the red LED

Those are important configuration pins because all of its link to the filter circuit, amplifier and interface with microcontroller.

To make this works, we need IR LED current stabilizer LED current is between 5mA and 40mA. We will used LT1932 circuit for it. Therefore, for the transimpedance, we choose this because photodiode will produces a strong tendency for the amplifier to go into oscillation at some high frequency above the gain bandwidth cutoff. This problem can be eliminated by adding a small capacitor in the feedback loop, which lowers the gain at very high frequencies. For the filter circuit we'll we use the Sallen-Key Low Pass Filter which are buffer circuit. And the output of it will interface with the microcontroller which will send the signal to the Smartphone using GSM.

That's all for now......See you again...Will come back in next week probably..