circuit implementation doubt

[Mridu]

Hi all,

I have designed a circuit for recording normal breath signal.........it has an instrumentation amplifier(ina101hp)and a low pass filter..........the Instrumentation amplifier INA101HP has been designed with a gain of 5.......Low pass filter also has a gain of 19..........i am recording breath signal using piezo disc............the problem with my circuit is i do not get the output from low pass filter and also the IA output is also not stable.......the output from instrumentation amplifier (when it is present) is about 1.47Hz............can this be given to a PC soundcard for recording?

regards
mridula

 

[LvW]

I am afraid, without a circuit diagram nobody can help you.

 

[Mridu]

hi there........this is my circuit diagram............pls chk it and find the fault

 

[FvM]

A popular fault in applying instrumentation amplifiers is to forget the required input bias. If this is your complete circuit, welcome to the club.

I also guess, that your low-pass has a cut-off frequenc in the x*10 Hz range and uses 18.2k rather than 18.2 ohm resistors.

 

[Mridu]

yes it is true...........mine is 18K resistors..........

A popular fault in applying instrumentation amplifiers is to forget the required input bias. If this is your complete circuit, welcome to the club.

I also guess, that your low-pass has a cut-off frequenc in the x*10 Hz range and uses 18.2k rather than 18.2 ohm resistors.

 

[Mridu]

hi there...............i tried to reduce the offset voltage with trim pot but it was not at all useful.........and also DC WAS 29.0v without any input.........any reasons?

 

[alexan_e]

The two power supply for U1 are reversed in the schematic, is this just a schematic mistake?

Alex