Proximity Flasher

[Watson A.Name - \"Watt Su]

I'm thinking about how to build a flasher that changes its rate as
someone gets close to it. Maybe about 1 Hz normally, and it speeds up
to 3 or 4 Hz when a hand or other body part gets close.

I thought about using two RF osc's with one having a sensor plate
connected to the tank. I already made a prox'y circuit using a single
RF osc at about 470kHz, but it has poor sensitivity, it takes a hand at
no more than 3/4" ( 20mm) from the plate to set it off. I'm looking for
something that's at least 6" (15cm), or maybe double that. The plate
shouldn't be too big, maybe a foot (30cm) square.

I'm looking for any ideas on how to implement the circuit. Thanks.
Some proximity detector schems..
What on earth is this thing supposed to do? Nothing, I'd guess.
http://www.zen22142.zen.co.uk/Circuits/Alarm/radiowavealm.htm

Another proximity circuit. The one I built is essentially this one, but
uses just discrete transistors, and a relay instead.
http://www.geocities.com/IECMaster/circuits_alarm/cir_alarm005.html


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[Jonathan Kirwan]

On Sun, 31 Oct 2004 23:54:24 -0800, "Watson A.Name - \"Watt Sun, the Dark
Remover\"" <NOSPAM@dslextreme.com> wrote:

I'm looking for any ideas on how to implement the circuit. Thanks.

Theremins come to mind for ideas on this.

Jon

 

[Watson A.Name - \"Watt Su]

"Jonathan Kirwan" <jkirwan@easystreet.com> wrote in message
news:4krbo0hj5tb4mjmd02lqab4pd3sl0bolhp@4ax.com...

On Sun, 31 Oct 2004 23:54:24 -0800, "Watson A.Name - \"Watt Sun, the
Dark
Remover\"" <NOSPAM@dslextreme.com> wrote:

I'm looking for any ideas on how to implement the circuit. Thanks.

Theremins come to mind for ideas on this.

Thanks. I ran across something interesting on this guy's theremin page.
But if you had looked at my text that you deleted, you would've seen
that the idea I had first mentioned, two oscillators, was basically just
that: a theremin. Except at a much lower freq, of course.

Thanks again.

> Jon

 

[Tim Williams]

"Watson A.Name - "Watt Sun, the Dark Remover"" <NOSPAM@dslextreme.com> wrote
in message news:10ocg31ckvi4c72@corp.supernews.com...

Thanks. I ran across something interesting on this guy's theremin page.
But if you had looked at my text that you deleted, you would've seen
that the idea I had first mentioned, two oscillators, was basically just
that: a theremin. Except at a much lower freq, of course.

No, actually Theremins are right around 432kHz.

You're on the right track, you just need to get them isolated. If that
still isn't sensitive enough (I'm talking a hertz or two difference, easily
detectable versus zero, when the oscs are locked), raise the frequency. Mr.
Theremin actually made security alarms using the system, so it's not
impossible.

If you can set rest offset to 1Hz and get the position and geometry
(possibly with shielding) of the antenna to raise it to 5Hz or whatever, you
might have exactly what you want, right out of the mixer.

Tim

--
"I've got more trophies than Wayne Gretsky and the Pope combined!"
- Homer Simpson
Website @ http://webpages.charter.net/dawill/tmoranwms

 

[Watson A.Name - \"Watt Su]

"Tim Williams" <tmoranwms@charter.net> wrote in message
news:10od536fbmr7a03@corp.supernews.com...

"Watson A.Name - "Watt Sun, the Dark Remover"" <NOSPAM@dslextreme.com
wrote
in message news:10ocg31ckvi4c72@corp.supernews.com...
Thanks. I ran across something interesting on this guy's theremin
page.
But if you had looked at my text that you deleted, you would've seen
that the idea I had first mentioned, two oscillators, was basically
just
that: a theremin. Except at a much lower freq, of course.

No, actually Theremins are right around 432kHz.

You're on the right track, you just need to get them isolated. If
that
still isn't sensitive enough (I'm talking a hertz or two difference,
easily
detectable versus zero, when the oscs are locked), raise the
frequency. Mr.
Theremin actually made security alarms using the system, so it's not
impossible.

If you can set rest offset to 1Hz and get the position and geometry
(possibly with shielding) of the antenna to raise it to 5Hz or
whatever, you
might have exactly what you want, right out of the mixer.

Yeah, that's what I was thinking, too. The only thing that really
concerns me is the stability of the oscs and thermal drift. I was
thinking of reducing the freqs of the oscs to somewhere down in the
audio range.

Tim

--

 

[Rich Grise]

On Tue, 02 Nov 2004 22:46:05 -0800, Watson A.Name - "Watt Sun, the Dark
Remover" wrote:

"Tim Shoppa" <shoppa@trailing-edge.com> wrote in message
"Watson A.Name - \"Watt Sun, the Dark Remover\""
news:<10oe00mdhmjv019@corp.supernews.com>...
Ultrasonic rangefinders come to mind. Some have a rather broad
(30-40
degree) sensitivity cone.

Optical (usually IR) rangefinders also work at these distances.

I think I need to clarify something. I didn't intend for the
flasher to
zwitch from low to high freq, I intended to have it vary in response
to
the distance the target is from the sensor. In other words, it's an
analog type of sensing system.

Both ultrasonic rangefinders and optical rangefinders are available
with
analog (linear in distance) outputs. Check the robotics newsgroups.

It is possible that ultrasonic rangefinding is ruled out by your
shortest-distance-to-sense requirement (which you've never really
told us). Commercial modules (e.g. Sonaswitch MINI-S) work well over
a distance of a few inches to several feet. There are pots on the
MINI-S
for adjusting the proportionality constants; they really *are* linear.

Thanks for the info. Altho I'm not averse to spending the money to get
something like this, I think my original intent on posting this was to
get some kind of feel as to how to design one myself. The theremin idea
was kind of what I had in mind when I started this, except that I
thought that the freq of a real theremin would be much too high. Yeah,
it's great for freq change over most of the audio freqs, but I think it
would be too sensitive and prone to drift at low freqs. But then maybe
if the theremin output was divided by a factor of 100 or maybe more.
The output pulse would be slower than 1 per sec, on up to several per
sec and maybe 10, 20, or more per sec.

What if, rather than dividing the theremin's frequency, you fed it
to a really wide filter, but had it sitting on the edge? i.e. freq.
to DC, and from there to your VC flasher? Or just the variable osc.
from the theremin, with a detuned filter? I.e., don't beat it and
detect audio, but detect the "RF", on the slope of a filter - this
should help swamp out some drift as well, I'd think.

Part of what I'm looking for is what method of sensing should be used.
Would ultrasonic be better?

Just by seat-of-the-pants, I'd say ultrasonic would be good in a range
like the range of those Polariod ultrasonic-focus cameras, which I
hear they used for the alitmeter in the Gossamer Brick, combined
with something theremin-like for close range? Or is that too much
stuff?

Actually, if I could get a transducer that
was high enough freq, like a tweeter and electret mic, then maybe just
using doppler effect might be enough to get the change in freq. But the
problem here is that it's the motion, not the proximity, that changes
the flash rate.

Remember those potted plants of years ago that had a microphone and amp
and motor driver, and the silly plant danced around when some noise was
made? Well, that was just on-off. I'd like it to be more proportional
to the distance or motion or sound, etc. Maybe I should have torn
apart a Furby or two or a tickle me Elmo to find out what they used..

Oh, that's just a mic, amp, and comparator.

But, what have you got so far?

Thanks,
Rich

 

[Watson A.Name - \"Watt Su]

"Tim Shoppa" <shoppa@trailing-edge.com> wrote in message
news:bec993c8.0411030616.33fc1b24@posting.google.com...

"Watson A.Name - \"Watt Sun, the Dark Remover\""
NOSPAM@dslextreme.com> wrote in message

news:<10ogvne8an5qg49@corp.supernews.com>...

was high enough freq, like a tweeter and electret mic, then maybe
just
using doppler effect might be enough to get the change in freq.
But the problem here is that it's the motion, not the proximity,
that changes the flash rate.

Remember, v = dx/dt. To get from one to the other all you need is
an integrator or differentiator. Now, the problem with going from
velocity
to distance is the initial condition .

Remember those potted plants of years ago that had a microphone and
amp
and motor driver, and the silly plant danced around when some noise
was
made? Well, that was just on-off. I'd like it to be more
proportional
to the distance or motion or sound, etc. Maybe I should have torn
apart a Furby or two or a tickle me Elmo to find out what they
used..

Those are all dead-simple microphone+peak detectors or squeeze
switches.
There is something to learn from them but you will never get a
proportional
output from them.

If you truly are looking for something that can sense distance, look
over the robotics newsgroups and the industrial sensor catalogs.

There are several manufacturers with level-detection through walls
with
capacitance chips, and with microwave level detector modules. Again,
look in the industrial sensor catalogs/app notes.

Thanks, but it scares me to think that I have to start getting into
microwaves to get something that's just a simple flasher.

I have an old 640x480 digital camera with autofocus, maybe if I tap into
the circuit that does the autofocus, I can get a distance proportional
voltage. ) All I have to do is mount it on a tripod, and let it
autofocus.. Whirr,whirr..

I saw a theremin in the latest issue of EPE (latest considering that B&N
take a few weeks to get it shipped it over here and put it on the
shelves). It used a pair of transistors in a Colpitts, I believe it
was. Each osc had a 1 mH choke. The proximity switch I mentioned I
made uses a similar circuit. I was surprised that when I first built
it, it was up around 560 kHz, so I could pick it up with an AM radio,
but at distances any greater than 3 feet (1m) the signal was too weak to
pick up. The collector resistor is 2.7k, so there's not a lot of power
to the osc. I tried this with a 6 foot (2m) wire in place of the sensor
plate, but it didn't help much in radiating the RF.

For the theremin, I'm going to need an antenna from an FM radio, I
guess. I'll have to check out what's available at rat shack, or else
some radio around here is going to look like it's been amputated! )

> Tim.

 

[Watson A.Name - \"Watt Su]

"Rich Grise" <rich@example.net> wrote in message
newsan.2004.11.03.16.49.29.352145@example.net...

On Tue, 02 Nov 2004 22:46:05 -0800, Watson A.Name - "Watt Sun, the
Dark
Remover" wrote:
"Tim Shoppa" <shoppa@trailing-edge.com> wrote in message
"Watson A.Name - \"Watt Sun, the Dark Remover\""
news:<10oe00mdhmjv019@corp.supernews.com>...
Ultrasonic rangefinders come to mind. Some have a rather broad
(30-40
degree) sensitivity cone.

Optical (usually IR) rangefinders also work at these distances.

I think I need to clarify something. I didn't intend for the
flasher to
zwitch from low to high freq, I intended to have it vary in
response
to
the distance the target is from the sensor. In other words, it's
an
analog type of sensing system.

Both ultrasonic rangefinders and optical rangefinders are available
with
analog (linear in distance) outputs. Check the robotics
newsgroups.

It is possible that ultrasonic rangefinding is ruled out by your
shortest-distance-to-sense requirement (which you've never really
told us). Commercial modules (e.g. Sonaswitch MINI-S) work well
over
a distance of a few inches to several feet. There are pots on the
MINI-S
for adjusting the proportionality constants; they really *are*
linear.

Thanks for the info. Altho I'm not averse to spending the money to
get
something like this, I think my original intent on posting this was
to
get some kind of feel as to how to design one myself. The theremin
idea
was kind of what I had in mind when I started this, except that I
thought that the freq of a real theremin would be much too high.
Yeah,
it's great for freq change over most of the audio freqs, but I think
it
would be too sensitive and prone to drift at low freqs. But then
maybe
if the theremin output was divided by a factor of 100 or maybe more.
The output pulse would be slower than 1 per sec, on up to several
per
sec and maybe 10, 20, or more per sec.

What if, rather than dividing the theremin's frequency, you fed it
to a really wide filter, but had it sitting on the edge? i.e. freq.
to DC, and from there to your VC flasher? Or just the variable osc.
from the theremin, with a detuned filter? I.e., don't beat it and
detect audio, but detect the "RF", on the slope of a filter - this
should help swamp out some drift as well, I'd think.

Sounds good. That's essentially what the 'other half' of the theremin
does. The oscillator is slope detected, and instead of a VC oscillator
it's fed into a VC amplifier, so the closer you get, the louder the
output.

THe only question is the circuit more complex and/or costly than the
divider? I'm willing to spend a few more pennies to use a divider chip
if it's all-in-one, rather than using a more complex VCO circuit.

Part of what I'm looking for is what method of sensing should be
used.
Would ultrasonic be better?

Just by seat-of-the-pants, I'd say ultrasonic would be good in a range
like the range of those Polariod ultrasonic-focus cameras, which I
hear they used for the alitmeter in the Gossamer Brick, combined
with something theremin-like for close range? Or is that too much
stuff?

Probably.

Actually, if I could get a transducer that
was high enough freq, like a tweeter and electret mic, then maybe
just
using doppler effect might be enough to get the change in freq. But
the
problem here is that it's the motion, not the proximity, that
changes
the flash rate.

Remember those potted plants of years ago that had a microphone and
amp
and motor driver, and the silly plant danced around when some noise
was
made? Well, that was just on-off. I'd like it to be more
proportional
to the distance or motion or sound, etc. Maybe I should have torn
apart a Furby or two or a tickle me Elmo to find out what they
used..

Oh, that's just a mic, amp, and comparator.

But, what have you got so far?

I mentioned the proximity switch I built, with such poor sensitivity
that I have to hold my hand 3/4" away from the sensor plate to trigger
it. Needs a serious boost in sensitivity. Also needs a whip antenna
and another oscillator.

Thanks,
Rich

 

[Watson A.Name - \"Watt Su]

"Tim Shoppa" <shoppa@trailing-edge.com> wrote in message
news:bec993c8.0411030625.7b36812e@posting.google.com...

"Watson A.Name - \"Watt Sun, the Dark Remover\""
NOSPAM@dslextreme.com> wrote in message

news:<10oh1reqdu3kjde@corp.supernews.com>...

A couple 'LS90s would give me / 100, what's a CMOS equiv, or is
there
one that'll divide by 100?

CD40102, 74HC390.

Thanks, I'll have to dig out one of those CMOS cookbooks I seldom look
at. I was thinking that / 256 would give about 1 pps at 256 Hz input,
and as the tone goes up to 5120 Hz at the high end of the theremin's
range, that should be about 20 pps, which is about as fast as the eye
can see a flicker. ANd everywhere in between.

> Tim.