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capacitive proximity detection

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






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V

Vladimir Vassilevsky

Jan 1, 1970
0
Terry said:
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).

[...]

The simplest thing to build is a basic single transistor RF generator
and a frequency counter with decision logic. L ~ 10uH C ~ 47pF, a 1m rod
as antenna. This arrangement can reliably detect a human body from about
2..3m.

Vladimir Vassilevsky

DSP and Mixed Signal Design Consultant

http://www.abvolt.com
 
L

LVMarc

Jan 1, 1970
0
Terry said:
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 =---------
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given complete flexability of antennas you can choose from many
different frequencies. You can extend the rnage beyond 1MHZ and include
al the ism band, 433 mc 918 mcc. 2.4 GHZ, etc... Higher frequency makes
for smaller and more directive antennas, if you need to "point" in a
given direction.

at 1-2 meters away you are not technically a capacitive snsors. as
those are typicall thought of as memebrane switches and the simialr 1mm
to 100 mm spacing. and of couse raltive to the wave number in an rf system.
 
D

D from BC

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 =----------------
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~$1.00 for wireless motion sensor on Ebay..
http://cgi.ebay.ca/GE-Wireless-Infr...QQihZ001QQcategoryZ115940QQrdZ1QQcmdZViewItem


D from BC
 

neon

Oct 21, 2006
1,325
Joined
Oct 21, 2006
Messages
1,325
you can buy these from china for $20 uses photocell good to 20 yards you can desentize to whatever. any movement in that range peeb even a dog. try harborfreight.com.
 
W

Winfield

Jan 1, 1970
0
Terry said:
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.

OK. Analog Devices makes some very sensitive and impressive
capacitance-measuring chips that should work just fine for you.
 
D

Don Lancaster

Jan 1, 1970
0
Terry said:
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/ =-

a one foot distance is pretty much an extreme range for a capacitive sensor.

Why not us an IR motion detector instead?
these do require a warm moving target, but otherwise are simple and cheap.

--
Many thanks,

Don Lancaster voice phone: (928)428-4073
Synergetics 3860 West First Street Box 809 Thatcher, AZ 85552
rss: http://www.tinaja.com/whtnu.xml email: [email protected]

Please visit my GURU's LAIR web site at http://www.tinaja.com
 
D

Don Lancaster

Jan 1, 1970
0
Don said:
a one foot distance is pretty much an extreme range for a capacitive
sensor.

Why not us an IR motion detector instead?
these do require a warm moving target, but otherwise are simple and cheap.

Otherwise, Analog Devices have some new capacitive sensors that have
insane differential sensitivity. One zillionth of a wumptofarad.



--
Many thanks,

Don Lancaster voice phone: (928)428-4073
Synergetics 3860 West First Street Box 809 Thatcher, AZ 85552
rss: http://www.tinaja.com/whtnu.xml email: [email protected]

Please visit my GURU's LAIR web site at http://www.tinaja.com
 
S

Spehro Pefhany

Jan 1, 1970
0
Otherwise, Analog Devices have some new capacitive sensors that have
insane differential sensitivity. One zillionth of a wumptofarad.


Freescale (nee Motorola) has had the MC33794 e-field chip out for some
time, and a cheaper version as well, but I don't know about the range.
The main target application, IIRC, is to detect the size of a human
sitting in a car seat in order to attempt to avoid killing them with
airbag deployment.


Best regards,
Spehro Pefhany
 
R

Rich Grise

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).

Is the application simply to sense humans, or is it a learning experience
in designing/building a proximity sensor?

If all you want to do is sense people, then you could buy off the shelf:
http://www.privatedoor.com/

That's just the first of "about 1,450,000 for automatic door openers." ;-)

Otherwise, I'd think a man-sized loop a la a big metal detector, then just
sense when the oscillator freq. deviates.

Good Luck!
Rich
 
M

Michael A. Terrell

Jan 1, 1970
0
Don said:
Why not us an IR motion detector instead?
these do require a warm moving target, but otherwise are simple and cheap.


What if he's trying to detect lawyers? ;-)


--
Service to my country? Been there, Done that, and I've got my DD214 to
prove it.
Member of DAV #85.

Michael A. Terrell
Central Florida
 
T

Tim Williams

Jan 1, 1970
0
Don Lancaster said:
a one foot distance is pretty much an extreme range for a capacitive
sensor.

Pah! Leon Theremin did ten times that, five decades ago!

Tim
 
a one foot distance is pretty much an extreme range for a capacitive

sensor.

Pah! Leon Theremin did ten times that, five decades ago!

Tim

Leon Theremin had a very interesting life and although not as widely
popularized as Nicola Tesla, I put him in the same catagory as others
who were "Ahead of Their Time". Theremin was famous for his musical
instruments that could be played by moving your hands/arms/feet in
proximity to straight wire or large diameter loop type antennas,
thusly named the "Theremin". He had some other contributions to
science and technology but they show in obscure references only with
out much detail. He was not into publishing his works or going after
financing in such a big way as Tesla was. It's about time for a
revival of the Theremin since nowadays synthesizer techinques are so
much easier and cheaper and so much more can be done than was possible
in the days of the Moog.


Staying on topic though...I'm sensing human body movement on the other
side of a wall so the IR and Ultrasonic suggestions are a NO GO !

Capacitive Proximity is a loose term and near field RF effects could
be argued to be both Electric and Magnetic Fields simultaneous as
either one will respond to a partially conductive body. It takes a
lot more energy to create a decent strength RF magnetic field a meter
or two away than it does an electric field.

I'm presently going along the lines that Vladimir Vassilevsky
suggested with single transistor oscillator, although I find I don't
need any long ferrite loopstick, but rather just a tiny ferrite drum
core. My L values are around 1mH and C values around 10pf or
essentially the tiny inductor's self-resonance. This makes the wire
antenna very sensitive to nearby capactive/conductive object effects.
The wire antenna needs to be a few feet long though. Ground is
essential. Kicking out a field thats a few volts per meter appears
ample strength to overcome background noise, and such a circuit can
run at 3V at 500uA which makes it tiny and battery power capable.

Seems little advantage between detecting frequency or amplitude
changes so I'm staying with amplitude changes for circuit simplicity.
I'm making use of positive feedback of the AM detected output back
into the transistor bias and this gives an over-all boost in
sensitivity, much like a Regenerative or Reflex style AM or Short Wave
receiver. I guess this method becomes useless if there's any nearby
radio station or shortwave transmitter, but I don't need long term
continuous reliabiliy and the rare false alarm is tolerable. I'm
thinking to do an array of these sensors to track movement between
various zones. The odd spurious single zone trip, can be ignored, as
can coincidental simultaneous all zone trips. I might even make the
detection differential so it only looks for crossover from one zone to
the next.

Giga Hz stuff always gets me into trouble! Maybe it's because my
prototyping techniques are bad but I always get microphonic
sensitivity from home-brew giga hertz circuits. Cutting and shaping
micro-stripline from scratch is such a pain! Even the meniscus size
from the amount of solder used can radically shift circuit parameters,
and the idea of pure inductance and capacitance seems to fade away at
those frequencies where everything you do inescapably involves
lossyness and tuned lengths? If I touch that stuff anymore, it's with
pre-assemble modules only. Seems it's still expensive and hard to
find raw parts that are useful in the 1-5 giga hertz range? A BITCH
to work with in all aspects IMHO. Giga Hz stuff bounces/refracts and
suffers high loss trying to penetrate most wall structures made of
modern construction materials. VHF might work though.

Thanks guys for the chip maker tips. Thought I had searched those
already but I must have missed something. Nothing in the IC realm I
found so far gave any app notes for distances or 1-3 meters so I did
not look into them further.... If you got a part # comes to mind or
you have used something before? that would help me zero in.

Any further tips or pointers along the lines of single transistor RF
oscillators and circuit topologies specifically for near field RF or
Capactive Proximity for humand body movement sensor or detection?
There's been some high-end Car Alarms where that technology has been
employed but I can't seem to find much details. There's a few patents
that refer to fence or perimeter type Intruder Alarms but they don't
give circuit details.

This is one of those technologies on the fringe that seems to have all
sorts of potential but never gets commercialized or exploited in a big
way. I wonder why?

I'm pleased to see the regulars in this group are still around!

Greets to you :)

~Terry Moreau
 

neon

Oct 21, 2006
1,325
Joined
Oct 21, 2006
Messages
1,325
H doesn't want help or ideas he is working on his own agaenda anything else is garage to him. This is my last entry on this subject.
 
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