Voltage Divider with Capacitor? Help!

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metallics2000

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voltage divider capacitor

Does anyone know what this circuit do? The input is from a heart rate infrared/phototransistor sensor. The output goes into an opamp.

To me it seems like the voltage divider is biasing the opamp and the capacitor is to block DC. But it also looks like its a highpass filter since the ouput to the opamp is taken after the capacitor. If it is ,why would it be a high pass filter instead of a lowpass filter? Or is this a combination of a highpass filter and does biasing for the opamp also? Any thoughts on this would be appreciated.

Thanks
 

I think your assumption about the resistors is correct. The 10K is probably the load for the photo sensor and the 47K is to charge the capacitor and isolate the amplifier to DC.

It does perform as a low pass filter but with those values, the -3dB point is well below 0.1Hz so I doubt it would block the signals from a heart rate monitor.

Brian.
 

What does highpass and lowpass filter do?
Can't see any filter in the above circuit.

Added after 1 minutes:

Where is the amplifier in the circuit above?
Transistor acts as amplifiers.Doesn't it?
 

You get probably get more information if you showed the opamp circuit connected, but the 10K is probably a load for the sensor (as already stated). The cap would be used to block DC signals. I would guess that the 47K resistor is only part of a resistor network for the opamp used to set the gain.

Show the whole circuit and I can probably give more precise answers.
 

Hi,

From the above arrangement, the input for precise op-amp is electrostatic effect.

signal is not constant one. that is continiously going to varry. during this change in input electrostatic energy potential also changed which is the input for op-amp.

That op-amp should be atleast OP07. Instrumentation amplifier is the right choice for this application.

Bye.
 

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