Nellcor DS-100A sensor for pulse oximeter

Started by winterwind, Mar 25, 2011, 15:39

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I found the pinout for Nellcor DS-100A sensor as :

pin1,4,6,8 : NC (in fact between pin 1 and 6 of the sensor is 7.5k resistor)
pin 2 : red wire; anode of the IR LED, cathode of the red LED
pin 3: black wire; cathode of the IR LED, anode of the red LED
pin 7 : cable shield, connects to copper shield over the phototransistor
pin 9 : phototransistor cathode
pin 5 : phototransistor anode, white wire; phototransistor detects level of IR and/or red light transmitted through the finger

I was able to use the leds, but stuck in getting signal out of the sensor. (I have connected pin 5 to Vdd (5V) through a pull-up transistor (since its the phototransistor), but I couldn't get the signal out at that pin (I just get a constant voltage  around 0.47V). Anybody give me a hint to get the signal out from the sensor......Thanks alot.
Nice day,



I know that you posted this a while back, so, probably you solved it already. But anyhow, first of all thanks a lot for the pinout. I was looking for that :)

I got it working on my case just by connecting the photodiode (PD, you call it phototransistor but anyhow, it is similar, I guess) to a transimpedance amp. In other words, you are looking for the current coming out. In my case, the TIA is differential input, but I guess you could have one PD terminal (cathode) to the minus terminal of the opamp, and the other (anode) to the plus. From the minus, there would be a feedback resistor (R) to the output. Output voltage will be photocurrent I (from the PD) x R (feedback resistor). Notice that the voltage drop/bias across the PD is set as zero and when light hits the diode, the photocurrent will flow from cathode to anode, out of the amp, creating a positive voltage/pulse at the output (TIA has very low input impedance).

Anyhow, let me know if you need any more details.


Paul Gardner-Stephen

The resister between pins 1 and 6 tells the pulse-oxy machine which callibration curve to use, based on variation in colour of the red LED:

1.  Connect the 6040 OHM 1.0% TEST RESISTOR from U27 pin 10 on the Processor PCB
  to (AGND). Alternate method is to place the resistor across pins 1 and 6 of the patient
  module if it is plugged in to the N-200

From page 5-7 of

See elsewhere in that document and also in for information on the use of calibration resisters.

Meanwhile, interested in any implementations you have come up with around these sensors (especially if on Arduino).  We are interested in making a very low cost pulse-oxy machine that can use these sensors.



I can provide original spo2 sensor(DS-100A and Philips M1191B etc),please conntact



I need you help. I put a voltage of 0.32 volts on pin 5 which goes to the positive input of my op amp (this was per a TI schematic which was tied to .39V, but I did not have the exact resistors for the divider). The negative op amp input is from pin 9. (BTW, feedback path on the op amp has a 500k resistor and a 3pf cap in parallel from op amp output to negative input, also as per the TI schematic).

I seem to be getting a very noisy signal and cannot seem to find my pulse! Should I put some caps between +/- of op amp? Are my connections backwards i.e. should I flip +/-? Is my voltage too low (if so should I increase to 0.39 or another value ???)

Thanks so much!



may i know the current ratings of IR and RED Led  used ......


Does anyone know where to get a Service Manual or Repair Manual for the Nellcor DS-100A sensors?
I have looked everywhere.


Hi Guy,

can anyone update me the output voltage of nellcor sensor prode ds100a?
i cant find any data sheet out there.

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