Pulse oxisensor

[ProFPGA]

I think the logical approach is to read the data sheets of an LED before designing their drive ckts , thanks all

 

[spec]

I think the logical approach is to read the data sheets of an LED before designing their drive ckts , thanks all

 

[Tony Stewart]

Actually a more logical solution is to define the required radiant flux and luminous intensity , Iv, to achieve good signal to noise ratio in the PD,,so that RED can be easily used to detect heart beats, then choose an LED which provides this Iv, then match the IR intensity so that calibration is easier before doing ratio metric O2 calculations bases on the relative transmission loss at two wavelengths.

Then using appropriate current control methods from precision voltage sources and precision value R's for each diode or CC limiters drive the LEDs accordingly.

Since Red lenses tend to be wider angle, Thus lower levels than IR diodes which are typically <10 deg , you will need at least 10,000 mcd from the RED diode to perform AC analysis of the detected signal with high gain to detect the modulated transmission loss from heart beats. ( I have bags of these custom parts here in Toronto )

The task of computing O2 depends on the ratio of received radiant flux ratios into a PD at two different wavelengths.

The task of detecting a heart beat is to amplify the modulated signal to extra the signal from the noise. Red wavelength modulation may be less than IR if your flux levels on a small detector are not high enough

. Therefore I conclude you have ignored the calculations necessary of achieving almost equal received flux levels in driver Iv, beamwidth, diffusion and area of detector. They should be exactly equal at the midpoint wavelengths between IR and R and cross over due to O2 content.

 

[Tony Stewart]

I think the logical approach is to read the data sheets of an LED before designing their drive ckts , thanks all

You are better off using 5V and an LM317 as a constant current sink for each LED to get precision regulated currents with a 1% R . See end of datasheet. Then use low side Nch MOSFET to enable the LED current.

any questions?

 

[spec]

You are better off using 5V and an LM317 as a constant current sink for each LED to get precision regulated currents with a 1% R . See end of datasheet. Then use low side Nch MOSFET to enable the LED current.

any questions?

Re arranging the deck chairs on the Titanic.

spec

 

[debe]

No one seems to have mentioned how these things actualy work. Theres a good article in January 2016 Silicon Chip magazine on how these things work. For a start the the IR & the Red LEDS are alternately switched on & off by a Micro processor to take the readings. They cant both be on at the same time.

 

[spec]

The OP is banned debe

spec