The Finger Oximeter

I'm trying to build a simple pulse oximeter using Ti's OPA380. So far I have the basic transimpedance circuit configured. If I wave either a red or infrared led in front of the sensor I get a several volt swing, showing that the circuit is at least partially working. I also get a swing of around 40-60mV when I place a finger on the sensor, place the red or IR led on my fingernail, and move the leds farther/closer to the fingernail. This tells me I'm getting a signal through the finger. But if I leave the IR and red leds directly on the fingernail the signal just stays stable, theres some noise even running off batteries, probably in the order of 10-15mV peak to peak. Has anyone done this before with the OPA380? Any circuit suggestions?

Thanks,
Dave

I would guess that the output of the opamp rails: reaches the maximum set by the supply voltage. If that's consistent with your test results, try to reduce the gain of your transimpedance opamp.

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