Hi. I am currently building a robot which is suppose to be able to detect and follow the magnetic field lines emitted from a beacon at a specific frequency.
Here is a simple run down:
source:
the beacon which is a coil of wires is connected to a wave generator which emits the magnetic field.
receiver:
there is a small 1mH inductor which is connected in parallel to a capacitor to make it resonate at the frequency of the beacon (not sure if needed)
the current induced by the magnetic field produces a voltage which is first buffered before being passed through an active bandpass filter.
the active bandpass filter consists of a simple second order highpass filter immediately followed by a second order lowpass filter. Both are unity gain with a bandwidth of 20000Hz.
Next the filtered voltage is passed through a series of amplifiers (4 stages)
Depending on the distance away from the beacon, a different stage is switched by a relay which connects it to a peak detector.
All opamps in use are TL071's and the problem that I have is that when it gets to the 3rd stage, there is some degree of noise.
I have been told to use smaller gains and when I connect a stage to the peak detector, I notice that the voltage drops considerably. I have tried buffering it before it enters the peak detector but no luck.
I have also put capacitors at the +/-V terminals of the opamp to prevent self oscillation
Any suggestions or comments about my circuit and this approach??
I was also wondering if its better to put the bandpass before or after the amplifiers and whether there should be gain, reduced bandwidth, etc..
Thanks!
Here is a simple run down:
source:
the beacon which is a coil of wires is connected to a wave generator which emits the magnetic field.
receiver:
there is a small 1mH inductor which is connected in parallel to a capacitor to make it resonate at the frequency of the beacon (not sure if needed)
the current induced by the magnetic field produces a voltage which is first buffered before being passed through an active bandpass filter.
the active bandpass filter consists of a simple second order highpass filter immediately followed by a second order lowpass filter. Both are unity gain with a bandwidth of 20000Hz.
Next the filtered voltage is passed through a series of amplifiers (4 stages)
Depending on the distance away from the beacon, a different stage is switched by a relay which connects it to a peak detector.
All opamps in use are TL071's and the problem that I have is that when it gets to the 3rd stage, there is some degree of noise.
I have been told to use smaller gains and when I connect a stage to the peak detector, I notice that the voltage drops considerably. I have tried buffering it before it enters the peak detector but no luck.
I have also put capacitors at the +/-V terminals of the opamp to prevent self oscillation
Any suggestions or comments about my circuit and this approach??
I was also wondering if its better to put the bandpass before or after the amplifiers and whether there should be gain, reduced bandwidth, etc..
Thanks!