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Help needed with Photodiode L14G3!

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yasser11

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l14g3 help circuit

Hi

I am using photodiode TIL 38 as an infrared source and using L14G3 as a detector. Between the diode and the detector I am keeping my finger so that the output at collector will vary according to the change in blood volume in the finger. By this i intend to measure the heart rate.

Can anyone help me in biasing the ckt. because I think I am not biaising it correctly. I am unable to get any output at the collector(it's totally random and no way near to what I am expecting) , also sometimes 50Hz wave (power supply noise) comes at the collector.

If anybody has any idea how to overcome these problems then do reply.
 

xcheck this construction too:


pay attention to following :
- phototransistors are not preferred as they easily get saturated
- emitter and detector diodes must be matched for wavelenth (detector should have max sensitivity at emitters wavelength)
- keep mechanical connection tight to the finger and wihtout gaps
- keep your finger in dark place to avoid 50 Hz or construct sensor mechanics to prevent external illumination impact on detector
- i used red light (600-670 nm) with no problem . Did not experiment with other wavelength.
- use one or more ultrabright leds to increase emitting light and keep transimpendance amplifier out of saturation. May be it is better to introduce light intensity reguilation - skin optical characteristic is very individual and different amount of light needed for different people to get it through and wihtout detector saturation. So may be AGC is better to done on sending side than receiving .
 

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