T
Terry Moreau
- Jan 1, 1970
- 0
Anyone have some circuit ideas, personal experience, or pointers to schematics for the above type of circuit?
I need to sense human body movement from about 1-2 meters away. I can arrange any sort of antenna(s).
My understanding is these circuits usually operate around 100kHz to 1.0Mhz range, and they work on the idea of sensing a change in near field RF reactance (human body makes a good capacitor to Earth) and/or loss factor (human body is partially conductive)
The sensing antenna is usually driven from a high source-Z and may also be sharply resonant with some self-compensating tuning/amplitude control since the small changes due to human body movement are masked by the bulk properties or the entire RF environment near the antenna. Bridge circuits, varactor diode, PLL, XTAL frequency reference....I have seen various techniques employed.
I have also read and personally found that making such tiny capacitance and electric field intensity change measurements is rather tricky in that your power source wires, and the processing circuitry itself, becomes unavoidably coupled into the measurement, unless battery operated and optocoupled.
Yes, I am aware of other sensing technologies however in this case I have settled in on capacitive proximity due to some unique conditions of the application that can't be avoided. So let's please not diverge off the topic OR if you feel compelled to bring up Passive Infrared, Doppler Radar, or UltraSonic then create a new thread.
Educated and experienced comments only please????
~Terry Moreau
--------------= Posted using GrabIt =----------------
------= Binary Usenet downloading made easy =---------
-= Get GrabIt for free from http://www.shemes.com/ =-
I need to sense human body movement from about 1-2 meters away. I can arrange any sort of antenna(s).
My understanding is these circuits usually operate around 100kHz to 1.0Mhz range, and they work on the idea of sensing a change in near field RF reactance (human body makes a good capacitor to Earth) and/or loss factor (human body is partially conductive)
The sensing antenna is usually driven from a high source-Z and may also be sharply resonant with some self-compensating tuning/amplitude control since the small changes due to human body movement are masked by the bulk properties or the entire RF environment near the antenna. Bridge circuits, varactor diode, PLL, XTAL frequency reference....I have seen various techniques employed.
I have also read and personally found that making such tiny capacitance and electric field intensity change measurements is rather tricky in that your power source wires, and the processing circuitry itself, becomes unavoidably coupled into the measurement, unless battery operated and optocoupled.
Yes, I am aware of other sensing technologies however in this case I have settled in on capacitive proximity due to some unique conditions of the application that can't be avoided. So let's please not diverge off the topic OR if you feel compelled to bring up Passive Infrared, Doppler Radar, or UltraSonic then create a new thread.
Educated and experienced comments only please????
~Terry Moreau
--------------= Posted using GrabIt =----------------
------= Binary Usenet downloading made easy =---------
-= Get GrabIt for free from http://www.shemes.com/ =-