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PICList Thread
'Proximity Sensing - PIC, Discretes, or Prebuilt?'
1999\04\14@215048 by Jason Harris

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Hello,

As part of an undergraduate design course in electrical engineering, my
team is designing an automated soap dispenser.  This will work like the
toilets and sinks that are becoming common; the presence of a hand under
the soap dispenser will trigger the soap flow.

As a long-time PIC fanatic, I'm immediately tempted to use an IR
emitter/detector and modulate the signal around 30 kHz (got the 'k'
right, too) and trigger off of new reflections.  However, this may be
overkill for this project.  I'm interested in seeing which solution
people more experienced than me recommend.  The major constraints are
development time (I've only got a couple of weeks) and cost.  Size is a
secondary constraint.

As I see it, these are the (viable) options:

    1)  PIC, IR emitter/detector

    2)  CdS cell, RC circuit(s), comparator

    3)  some external company's prebuilt module (I'd need to know the
company, and probably their part number)

    4)  something else (capacitive, inductive, lasers, ultrasound, heat,
microwave, etc)

I'm tempted to go with option 3) since it's the easiest and I've got a
pretty strong A already in the design class and I'm running out of design
time.  However, two hours of internet searching hasn't netted me anything
useful.

Option 1) doesn't seem too bad, but it's actual work, and a PIC is
probably overkill for a project this simple.

However, I still need to time the soap flow, and the delay between
dispenses and assorted stuff, so the PIC might still be the best option.

Opinions?  Ideas?

Jason Harris
Senior, Electrical Engineering
Arizona State University

P.S.  What with the recent controversy on the PICList, I'm not as sure as
I should be that this is actually on-topic, although it sure as hell
seems like it should be to me.  In any case, if despite my two years of
lurking, I've misunderstood the newly evolving etiquette, it was
unintentional.

1999\04\14@234656 by Sean Breheny

face picon face
Hi Jason,

Sounds like you have an interesting project!

At 06:50 PM 4/14/99 -0700, you wrote:
>As I see it, these are the (viable) options:
>
>     1)  PIC, IR emitter/detector

Sounds like a good bet to me. The IR reflectivity of skin is pretty high
(although,I guess you ought to check it with different skin tones,too).

Would it be possible to have a lower extension of the dispenser so that the
hand would break a beam?

>
>     2)  CdS cell, RC circuit(s), comparator

Be careful. CdS cells have a very slow response time (can be as low as
several seconds under certain light conditions!)

>
>     3)  some external company's prebuilt module (I'd need to know the
>company, and probably their part number)
>

Sorry, don't know one off hand,but you can check http://www.mpja.com

>     4)  something else (capacitive, inductive, lasers, ultrasound, heat,
>microwave, etc)

Ultrasound is another good bet,although it might be tough to deal with
additional reflections from other objects.

>Option 1) doesn't seem too bad, but it's actual work, and a PIC is
>probably overkill for a project this simple.
>
>However, I still need to time the soap flow, and the delay between
>dispenses and assorted stuff, so the PIC might still be the best option.

I think that in a real life design, a small PIC (12C508) would be best. If
you want to get more practice with various types of other ICs,then you
might explore that route,but a PIC would make for a more compact and
simpler design, I think.

{Quote hidden}

I recently checked with Jory and Mark about what topics are grounds for
getting kicked off. No reasonable technical discussion is grounds for
getting kicked off, although, one should still exercise judicious use of
[OT] and judgement about carrying out extended way OT threads (yeah, I
guess I should tell myself "Look who's talking!"). However, I agree that
this is FIRMLY ON TOPIC,and I'm sure Jory and Mark would agree on this,too.




|
| Sean Breheny
| Amateur Radio Callsign: KA3YXM
| Electrical Engineering Student
\--------------=----------------
Save lives, please look at http://www.all.org
Personal page: http://www.people.cornell.edu/pages/shb7
spam_OUTshb7TakeThisOuTspamcornell.edu ICQ #: 3329174

1999\04\15@011728 by Tjaart van der Walt

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face
Jason Harris wrote:
{Quote hidden}

How about a more powerful laser and a smoke detector? <GRIN>

Seriously, I'd go with a modulated IR LED. Check the received
level during on-time and during off-time with the A/D. A
difference would indicate the presence of dirty hands.


> P.S.  What with the recent controversy on the PICList, I'm not as sure as
> I should be that this is actually on-topic, although it sure as hell
> seems like it should be to me.  In any case, if despite my two years of
> lurking, I've misunderstood the newly evolving etiquette, it was
> unintentional.

This is not off-topic in my books. This falls very nicely
into the what-pics-connect-to category.

--
Friendly Regards          /"\
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.....tjaartKILLspamspam@spam@wasp.co.za  / \ AGAINST HTML MAIL
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|R&D Engineer : GSM peripheral services development|
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1999\04\15@020410 by Gabriel Gonzalez

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face
Check out http://www.qprox.com

Gabriel

-----Original Message-----
From: Jason Harris <.....smegtraKILLspamspam.....GOODNET.COM>
To: EraseMEPICLISTspam_OUTspamTakeThisOuTMITVMA.MIT.EDU <PICLISTspamspam_OUTMITVMA.MIT.EDU>
Date: Wednesday, April 14, 1999 8:45 PM
Subject: Proximity Sensing - PIC, Discretes, or Prebuilt?


{Quote hidden}

1999\04\15@041248 by Julian Fine

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Hi,
Be very careful when using a varying light source to trigger something like
a soap dispensor. If you travel a bit you will fine that in most toilets the
hot air dryers switch randomly on off and at our main airport the water taps
are also light controlled and waste a lot of water.
Rather use a beam of infra red that when broken triggers a 555 and dispenses
some soap. Cheap and nasty to make but effective.

        Julian Fine
  Eagle Wireless Security
http://www.eagle-wireless.co.za



{Original Message removed}

1999\04\15@043354 by Tjaart van der Walt

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Julian Fine wrote:
>
> Hi,
> Be very careful when using a varying light source to trigger something like
> a soap dispensor. If you travel a bit you will fine that in most toilets the
> hot air dryers switch randomly on off and at our main airport the water taps
> are also light controlled and waste a lot of water.
> Rather use a beam of infra red that when broken triggers a 555 and dispenses
> some soap. Cheap and nasty to make but effective.

Cheap & nasty - sure, but with a beam, you would have
to have a transmitter and a receiver opposite each other.
this implies that at least one (in the vertical case),
or both (in the horisontal case) will have to be exposed.

Have you ever seen a clean restroom? The exposed lens
will be grubby and opaque within weeks.

If you use the reflected IR, and *compare* the light
levels for the TX-on and TX-off cases, you'd be compensating
for ambient light, 50Hz/60Hz etc. Because both TX and RX will
point downwards, you could protect them from washcloths and
hide them from vandals.

I have seen a 555-driven IR beam that could have had more
range if the TX-on state was compared to the TX-off state with
a cheap PIC ;) If I remember correctly, its range was 15m. Hehehe

--
Friendly Regards          /"\
                         \ /
Tjaart van der Walt        X  ASCII RIBBON CAMPAIGN
@spam@tjaartKILLspamspamwasp.co.za  / \ AGAINST HTML MAIL
|--------------------------------------------------|
|                WASP International                |
|R&D Engineer : GSM peripheral services development|
|--------------------------------------------------|
| Mobile : KILLspamtjaartKILLspamspamsms.wasp.co.za  (160 text chars) |
|     http://www.wasp.co.za/~tjaart/index.html     |
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1999\04\15@045716 by Julian Fine

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Hi,
I aggree with tjaart but are we not forgetting that if the dispensor does
not run for 5 years on a 9 volt battery, never run out of soap, be able to
withstand a 7 on the richter scale, be completely water and vandel proof,
have a excellent k factor and cost less then 1 dollar nobody will buy it.
HAHaHa.

        Julian Fine
  Eagle Wireless Security
http://www.eagle-wireless.co.za


{Original Message removed}

1999\04\15@064240 by paulb

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face
Gabriel Gonzalez wrote:

> Check out http://www.qprox.com

 I think you actually meant http://www.qprox.com/  Fascinating device.
Curious similarity to a 12C508 ;-)

 I do fancy you could do it with a PIC, especially noting the
requirement that the integrating cap be much larger than the sensor
capacity.
--
 Cheers,
       Paul B.

1999\04\15@091423 by Harrison Cooper

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face
Lets remember this is a senior project...not a real consumer product.  Most
of the folks doing senior projects don't have a luxury of being sponsored (I
was fortunate...had the FAA sponsor mine).


I aggree with tjaart but are we not forgetting that if the dispensor does
not run for 5 years on a 9 volt battery, never run out of soap, be able to
withstand a 7 on the richter scale, be completely water and vandel proof,
have a excellent k factor and cost less then 1 dollar nobody will buy it.
HAHaHa.

1999\04\15@100215 by Mike Keitz

picon face
On Wed, 14 Apr 1999 18:50:43 -0700 Jason Harris <RemoveMEsmegtraTakeThisOuTspamGOODNET.COM>
writes:

>As a long-time PIC fanatic, I'm immediately tempted to use an IR
>emitter/detector and modulate the signal around 30 kHz (got the 'k'
>right, too) and trigger off of new reflections.  However, this may be
>overkill for this project.

Consider a pyroelectric (passive IR) burglar detection sensor, as are
used in automatic floodlights and burglar alarms.  Remove the Fresnel
lens and turn the sensitivity way down and it will detect when a person's
hand is near it.  You may even want to put a tube around the sensor so it
just looks down at one spot.

If you use visible or IR light, definitely modulate it.  There's no need
for a detector module, justt use a phototransistor or photodiode.
Modulation frequencies of about 1 kHz are more practical, especially with
phototransistors since they are slow.  The process you want is called a
synchronous detector.  Sample the detector output while the LED is on
(just before turning it off) and while it is off (just before turning it
on), and subtract the two readings.  If no light is being returned the
result will be near zero, if light is being returned it will be positive.
Filter several of these reuslts, and if consistently positive assume
something was detected.

A PIC with ADC should be able to do everything internally, it may not
even be necessary to have an amplifier after the phototransistor.  If you
use a digitial-only PIC for the timers and short development time, a type
567 IC is good to serve as the oscillator, synchronous detector, filter
and threshold gate.  To use it in this mode, connect the loop filter
capacitor terminal to Vcc (this holds the oscillator at a constant
frequency) and drive the LED with a transistor driven from the oscillator
resistor terminal.  Keep the input level low.  The 567 doesn't work well
with too much input level.


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1999\04\15@102711 by Wagner Lipnharski

picon face
Mike suggestion to use the passive IR (burglar detection) is probably
the best one, ready to use, cost less than $10 and it is ready to
install.  Just disassembly it, install inside a wall switch box right
below the soap dispenser, adjust the sensitivity.  The device is ready
to control an electric lamp, so enough to control a solenoid to release
soap. You need to make sure the "turn off" time is adequate, if not,
lots of soap will go down the drain.

With enough space, it could be installed inside the soap dispenser,
"looking down", so surrounding interference would be reduced.

You could insert a PIC unit in the middle of the circuit, to control
timmings and generate a train of pulses for soap spits, but is it
necessary?

Wagner.

1999\04\15@123254 by Ralph Landry

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face
I found a proxi sensor from Quantum Reasearch the QT110 (8 pin chip)
check http://www.qprox.com for data and samples.  This device was originally
made to turn on a faucet when you came close to it or touched the
faucet.  Looks like an interesting device for other apps as well.
-Ralph
spamBeGonerlandryspamBeGonespamhaywood.main.nc.us
"If they call it Tourist Season why can't we shoot 'em?"
ICQ# 19545315

1999\04\15@153202 by Jason Harris

picon face
If this were a one-of design, the PIR from a burglar detector sounds like
it would be the best idea, but I need to design for 50,000+ yield and do
a cost analysis.  I can't really tell the judging committee that we'll be
building these things by buying someone else's commercial product,
disassembling it, and installing it into our own :)

I'm thinking I'll be going essentially with the idea Mike Keitz put
forward - using one of the small ADC PICs and a phototransistor.  For me,
this is the easiest & quickest path.  The only problem is that I don't
really learn anything new :)

Thanks for all the replies!

jason




Wagner Lipnharski, While Chillin' on Dagobah with The Yodester, Uttered
this Krazy Krap...

{Quote hidden}

1999\04\15@171403 by Julian Fine

flavicon
face
Hi,
The idea to use a Passive IR detector is good now why dont you do the
following.
Use a pir detector with a circular fresnell lens and a tube of about 10mm
inside diameter and about 20mm long.
The lens is available from wavelenghtoptics.com ask Kris Matulich for the
same one that Eagle Wireless uses.
The lens is quit big but just cut a small circular part out of the middle.
Use an mc1776 low current op amp for the pir,( email me if you want the
circuit) and the output into a pic analogue pin. Use the pic to do the rest
which I am sure you know how. The low current op amp etc and letting the pic
sleep is so that the unit can be battery operated which I think is a must.
Total parts cost should be around 4 to 6 US dollars.
I hope this helpes as it is similar to a project I did for a Hotel chain to
open a vent when someone entered the toilet.

************* Julian Fine ***********
********** TakeThisOuTjulianEraseMEspamspam_OUTfine.co.za ********
******* http://www.fine.co.za *******
*** http://www.eagle-wireless.co.za ***


{Original Message removed}

1999\04\16@123954 by Brian Duran

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Hello

I too would go for the IR device, it would be really simply.  Unless you
need the Pic for controling how much soap is being dispense(I have no Idea
how this happens), just a 555 timer to modelate to transmit, a comparator
to set the level(maybe some amplification first) and a 567 tone decoder
might work, for only 1.50 in parts.

Brian

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