Custom AC power switch

[Jonathan Kirwan]

My autistic daughter has burned up a few microwave ovens. She loves to cook,
but places the popcorn inside and then presses 3 3 3 and START. Since that is
3:33 minutes and since the popcorn only wants 2 minutes, it often burns horribly
or else bursts into flame.

Having a "popcorn" button on the microwave is completely useless. I've tried to
teach her to use it, but she is about like a 3 year old and simply won't get the
picture. So I considered the idea of plastic cards with pictures on them that
she could "bring near" or "wave" by the front panel of the microwave unit, but
I'd need to completely redesign the front panel electronics and ... I'd rather
not attempt to bite that one off, just yet. It's an idea that would probably
work, and I've tried to interest Amana/Maytag in the idea of fielding UL
approved microwave units for "special needs," but the interest was nearly zero.

She's also very good at plugging things in, if the plugs are visible. Hot plate
burners, toasters, microwave ovens, toaster ovens, etc. If it can be plugged
and she thinks she might be able to make a melted cheese sandwich in the middle
of the night, well.... I might wake up to a terrible smoke in the house, because
she found a burner we'd set aside and plugged it in and got a pan and bread
slices and cheese and forgot about the whole thing, after turning on the burner.

We have to be able to cook, ourselves, with some level of convenience. And
locking everything up, keeping the main power breakers off for the main stove,
etc., makes doing routine things not nearly so routine. Since the main problem
in her habits is the microwave unit, I placed it into a cabinet with power where
she cannot see or reach it. When I need to use it, I pull the entire unit out
into my arms, reach back and plug it in, place it back and then use it. Then
reverse the process, if I'm not otherwise distracted. If I do forget, I can
often expect another burned bag of popcorn a few hours later.

I can arrange to place a hidden switch, I suppose. But I don't want to bring AC
power out to a switch near someone's fingers and it wouldn't solve my forgetting
to switch it back (having a 20 year old running around the house, with a playful
mind of a 3-5 year old, leads to many distractions and I'm not getting any
younger and my memory isn't quite as good as it once was.) So I started
considering other options, such as low-voltage signaling, etc., for a remote
power switch I could hide inline with the microwave unit behind the cabinet and
which would automatically turn off the power supply, even if I forgot.

(I'm no analog power designer. A small time hobbyist and an embedded programmer
type.)

I'm imagining this functionality:

* A pneumatic switch driven by aquarium tubing, where I can snip off
an appropriate amount from the point of the AC power controller back
to some convenient location where I will place a bladder/bulb that I
can squeeze when I want to enable to power to a device/circuit. This
would start/initiate the circuit.

* A self-contained power controller unit with an AC-in and an AC-out,
and a nipple for that aquarium tubing (goes to the pneumatic switch
inside, which feeds a microcontroller's input pin to notify it.)

* The ability to control a single 15 amp circuit at 125V RMS AC, 60 HZ.

* The system would do several things, once activated. First, a timer
starts (programmable by means I can determine) and the power simply
stays ON for this duration, no matter what. Second, if in that time
the circuit draw exceeds about 0.1 amp, then the circuit stays enabled
so long as that draw or more continues without abatement. If it does
fall back to near zero, then the timer overrides if there is still
more time. If not, the circuit goes OFF 20 seconds after the load is
removed. I need to reactivate it, if I need to reuse it.

* I'm not looking for dimming, here. This is an ON/OFF controller, not
a zero-cross, cycle-by-cycle or phase-angle dimmer.

* The time delay for the circuit can be programmed through the pneumatic
switch, using a "long-held pulse" on the bulb that the micro would
detect, followed by a series of short pulses to count up to the minutes
I'd like to program into it. A long pause after that would commit the
time to memory.

I can handle the mechanicals for the pneumatic switch, tubing, nipples, and
bulb. That's an easy and cheap part. I can also handle the microcontroller
circuit -- the digital parts of this. I believe I can also handle creating a
modest power handling circuit to supply the necessary DC for the micro (less
than a milliwatt total) and any zero-cross measurements of the AC cycles I may
need.

However, what I do not feel comfortable dealing with or making the better design
choices for turning the AC power ON and OFF, whether a relay, a TRIAC, etc., or
designing well for monitoring mean AC load current. And dealing with safety
issues I might not be aware of, even if the circuit is hidden away and not out
where someone might touch it. Because it might be hidden, I have to be sure it
is not going to create its own fire hazard.

I've been doing soldering and wiring for some 30 years now, so I'm now modestly
competent at decent layout, adequate wire selection for the currents needed, and
proper wiring harnessing.

I'm interested in existing devices to do this, first and foremost. I'd rather
not fabricate my own solution if one already exists that is close to what I
want. But if not, I'm interested in any viable options or ideas for the AC
power control and for the AC load current monitoring functions, from the
perspective of using a microcontroller.

Or suggestions about a "better way." (But on that score, no one else really
knows or understands exactly how we live our lives here and I'm the only proper
judge about what can work in our life style. My description above is
necessarily reduced from the truer reality. Still, I'm open to ideas.)

Jon

 

[Zak]

My autistic daughter has burned up a few microwave ovens. She loves to cook,
but places the popcorn inside and then presses 3 3 3 and START. Since that is
3:33 minutes and since the popcorn only wants 2 minutes, it often burns horribly
or else bursts into flame.

I would suggest the following: a box in the supply line that passes
power at low wattage. At higher current, it will cut teh power after a
time you thing is safe (mabe 2 minutes for the popcorn).

For the case where you want to extend the time, put a button on the box
that you have to push in the initial 2 minute period. This will leave
the power on indefinitely, until usage drops (you switch off the device)
and the operation is back at '2 minutes max'.

Now tehre is a problem with microwaves - at low wattage they cycle on
and off. Same with hobs with te thermostat. This could mean they restart
the cycle automatically. You may be able to avoid this using timers (do
not allow another automatic 2 minute cycle for the next 30 minutes, and
do not cut off 'high power' immediately in 'extend mode' when the usge
drops.

It sounds pretty elegant: you start things normally, and if needed press
the 'extend' button to keep the device on. Power the device off and
things are safe again.

Your daughter can also use things normally, but they will cut off before
they get dangerous.


Thomas

 

[Rene Tschaggelar]

My autistic daughter has burned up a few microwave ovens. She loves to cook,
but places the popcorn inside and then presses 3 3 3 and START. Since that is
3:33 minutes and since the popcorn only wants 2 minutes, it often burns horribly
or else bursts into flame.

Having a "popcorn" button on the microwave is completely useless. I've tried to
teach her to use it, but she is about like a 3 year old and simply won't get the
picture. So I considered the idea of plastic cards with pictures on them that
she could "bring near" or "wave" by the front panel of the microwave unit, but
I'd need to completely redesign the front panel electronics and ... I'd rather
not attempt to bite that one off, just yet. It's an idea that would probably
work, and I've tried to interest Amana/Maytag in the idea of fielding UL
approved microwave units for "special needs," but the interest was nearly zero.

I'm consider a blunt "adults are bigger" approach. The
kitchen area over a power relay with the remote being placed
on the ceiling. For an adult reachable with a chair. The light
needs to work without the relay though.

Rene

 

[Tony Williams]

My autistic daughter has burned up a few microwave ovens. She
loves to cook, but places the popcorn inside and then presses 3 3
3 and START. Since that is 3:33 minutes and since the popcorn
only wants 2 minutes, it often burns horribly or else bursts into
flame.

How about buying her her own microwave. A cheap
one with knob-controlled clock. Jigger the knob
so that it can only be turned to do two minutes.

Also have a timeswitch and contactor that shuts
off power to everything else the kitchen for those
hours when it is not likely to be used by you.
eg, midnight to 6am, or whatever.

 

[John Woodgate]

I read in sci.electronics.design that Jonathan Kirwan

My autistic daughter has burned up a few microwave ovens. She loves to
cook, but places the popcorn inside and then presses 3 3 3 and START.
Since that is
3:33 minutes and since the popcorn only wants 2 minutes, it often burns
horribly
or else bursts into flame.

Would you be prepared to fit key-operated power switches in the
appliances concerned?

 

[Tim Shoppa]

I know you want to roll-your-own, but look for the "industrial"
microwave ovens made by Amana et al over the past couple of decades.
These are designed for use in cafeterias etc.

Unlike consumer microwave ovens, which seem to sell themselves over how
many hundreds of buttons they can put on their front panels, these
cafeteria-type units have a much simplified system, often just a set of
buttons for some standard times. No enter, start, etc, necessary.
Disable all but one of the buttons and you're done.

Tim.

 

[Jonathan Kirwan]

Would you be prepared to fit key-operated power switches in the
appliances concerned?

I suppose I could. But the difficulty then would be that Athena would see us
doing that and start trying (and probably breaking) various keys. We'd soon
lose keys around the house, plus I'd probably need to get a locksmith involved
so that all of the locks used the same key (it would be a terrible pain to have
different keys for each lock.) Worse, it doesn't deal with the fact of my own
forgetfulness or distractions. I can easily imagine leaving the key inserted.
Or wasting time looking for one.

One of the things I'm also focused on are things that WASTE time in my life.
Barriers to getting things done efficiently. Scanning around for keys, just to
operate a device, is likely to add many short delays into my life. Not very
attractive. Especially, since Athena has often lost whole collections of our
keys because she becomes interested in things we are interested in.

Jon

 

[Jonathan Kirwan]

I know you want to roll-your-own, but look for the "industrial"
microwave ovens made by Amana et al over the past couple of decades.
These are designed for use in cafeterias etc.

Unlike consumer microwave ovens, which seem to sell themselves over how
many hundreds of buttons they can put on their front panels, these
cafeteria-type units have a much simplified system, often just a set of
buttons for some standard times. No enter, start, etc, necessary.
Disable all but one of the buttons and you're done.

Yes, but I also need to use the oven for myself, as well. Warm up soup, etc.
Not to mention that microwave ovens isn't my only problem that this would help
solve. I've many other electrical circumstances around the house that could use
the same solution I mentioned. I can't go around looking for industrial
solutions to each of these.

Jon

 

[Jonathan Kirwan]

How about buying her her own microwave. A cheap
one with knob-controlled clock. Jigger the knob
so that it can only be turned to do two minutes.

Been there, done that. She has access to the rest of the house and will use
everything in it. Having her own was an old idea we tried and it kind of works,
in the sense that she uses it at all and doesn't use the other one. But
inevitably, she walks to another part of the house and decides to use that one,
too.

Also have a timeswitch and contactor that shuts
off power to everything else the kitchen for those
hours when it is not likely to be used by you.
eg, midnight to 6am, or whatever.

Not convenient, though. My wife and I overlap our sleeping times so that one of
us is usually awake. Most of the day is covered by one of us. We don't have
normal hours that "normal folks" understand. And she doesn't sleep normal
hours, at all. It's as likely that she will be awake for 35 hours as it is that
she will be awake for only 15. She sleeps when she chooses to sleep.

Fixed times are simply going to get in the way. No question. And I'm really
trying to get rid of impediments, things that delay me for 20 seconds or 50
seconds are to be eliminated, not created.

Which is why I want a very convenient way that I can hide to turn things on that
will always be there for me when I need it, without having to think about it or
go find something or take a long walk to the power control panel downstairs.

Jon

 

[Jonathan Kirwan]

I'm consider a blunt "adults are bigger" approach. The
kitchen area over a power relay with the remote being placed
on the ceiling. For an adult reachable with a chair. The light
needs to work without the relay though.

She's 20 years old and very, very strong and agile. She has already moved
entire groups of furniture in order to reach things we've placed in hard to get
locations. She will move ladders around, get chairs, etc.

However, there are some things that can be made just enough "too complex" for
her to activate. For example, if I were to set up a bulb I'd squeeze in a
certain pattern to activate the power. She'd never learn it, though she would
know it is connected to the idea and would probably try.

Also, when she knows there is something that works for me and she cannot get to
it, she will pester me for hours on end to let her get access (if she cannot do
so, herself.) I want to reduce this, not increase it. If she has access to a
bulb, she will squeeze it. But I can arrange things so that it simply doesn't
work for her. Under those circumstances, she will give up and only try
occasionally. And she won't bother me about it, as she has access.

Chances are, as well, that if I make that aquarium tubing go far enough away
from the device involved, she won't make the connection. She might, but I've
got a much better chance that she won't. She'll just think I use magic to turn
on the power. Much the better.

She's learned over all theses years most of the normal methods used by real
human designers for human end-use. So whatever it is, it should NOT look like
one of those normal arrangements. This is one reason why keys/keylocks are a
bad idea in this context. She knows about them.

Jon

 

[Paul Mathews]

Have you considered the X10 system of AC power controls? You can
obtain IR and RF remotes, perhaps keep one in your pocket or turn
appliances on from another part of the house.

http://www.x10.com/home2.html

Paul Mathews

 

[Jonathan Kirwan]

Have you considered the X10 system of AC power controls? You can
obtain IR and RF remotes, perhaps keep one in your pocket or turn
appliances on from another part of the house.

http://www.x10.com/home2.html

I don't want to set up something like that. I'm looking to keep things simple,
effective, to cover my own memory loss should I be distracted and have to deal
with something else. Automatic shutoff is important, but not while the device
is being used.

And she absolutely LOVES remotes. Carries them around, loses them, etc. I'd
really be just asking for more delays in my life, that way.

Jon

 

[Rob Gaddi]

She's learned over all theses years most of the normal methods used by real
human designers for human end-use. So whatever it is, it should NOT look like
one of those normal arrangements. This is one reason why keys/keylocks are a
bad idea in this context. She knows about them.

Jon

You said you've got experience on microcontrollers, that certainly seems
to me to be the easiest way of addressing the control / interface
issues. With just two pushbuttons you can implement a fairly
innocuous security code system, something along the lines of BLUE GREEN
GREEN BLUE GREEN BLUE BLUE. Or for not too money you could get a full
blown keypad, though that might actually serve your needs less well.

Check into TI's MSP430 microcontrollers. They've got a couple good app
notes regarding using them to control things on the mains, and the
development kits provide you with the JTAG emulator and software for
about $100.

 

[Jonathan Kirwan]

You said you've got experience on microcontrollers, that certainly seems
to me to be the easiest way of addressing the control / interface
issues. With just two pushbuttons you can implement a fairly
innocuous security code system, something along the lines of BLUE GREEN
GREEN BLUE GREEN BLUE BLUE. Or for not too money you could get a full
blown keypad, though that might actually serve your needs less well.

Check into TI's MSP430 microcontrollers. They've got a couple good app
notes regarding using them to control things on the mains, and the
development kits provide you with the JTAG emulator and software for
about $100.

I'm using them, currently. I'll have to check into the apnotes, though, and see
what you are talking about. However, as my knowledge of TRIACs is very limited,
I suspect that I'll need to do some studying to be sure how to properly control
them via a micro-pin (I don't want to destroy the fragile output pin driver.)

Jon

 

[Spehro Pefhany]

I'm using them, currently. I'll have to check into the apnotes, though, and see
what you are talking about. However, as my knowledge of TRIACs is very limited,
I suspect that I'll need to do some studying to be sure how to properly control
them via a micro-pin (I don't want to destroy the fragile output pin driver.)

Jon

I suggest you use an MOCxxx opto-triac (to drive the output triac),
which uses a low-voltage IR led in the input, well suited for the
MSP430. Some are available with only 5mA trigger current, IIRC. It
will provide galvanic isolation as well.



Best regards,
Spehro Pefhany

 

[Jonathan Kirwan]

I suggest you use an MOCxxx opto-triac (to drive the output triac),
which uses a low-voltage IR led in the input, well suited for the
MSP430. Some are available with only 5mA trigger current, IIRC. It
will provide galvanic isolation as well.

Thanks for the suggestion. I'll look them up. The 5mA is about the limit I'd
want to consider for the MSP430 outputs.

I assume I'll need to re-trigger at each zero-cross? Should I be concerned
enough here to make sure I don't trigger until the AC voltage reaches some
threshold for staying on? Or just re-trigger it in a short burst of pulses long
enough to be sure that's true?

Thanks,
Jon

 

[John Woodgate]

I read in sci.electronics.design that Jonathan Kirwan
ax.com>) about 'Custom AC power switch', on Wed, 9 Feb 2005:

I suppose I could. But the difficulty then would be that Athena would
see us doing that and start trying (and probably breaking) various keys.

That's why my proposal was tentative. Are you in touch with any support
groups? People have had your problems before; maybe they also have some
solutions?

 

[Jonathan Kirwan]

I read in sci.electronics.design that Jonathan Kirwan


That's why my proposal was tentative. Are you in touch with any support
groups? People have had your problems before; maybe they also have some
solutions?

I am. In fact, I've been active in volunteering about 300-500 hours a year for
perhaps 15 years now. So I know a lot of people in this area. I recently spoke
with a home contractor who is part of a corporation that specializes in special
construction for children like mine. In fact, he spent a few months working
here and teaching me while he worked on various aspects. When he and I talked
about this particular need (which he understands well), he had no real
suggestions and instead countered that if I came up with something that could be
UL approved, he'd probably use it in his own work, regularly.

It wasn't my intention to bite of UL approval. I just want to solve my own
problems, to be honest. But if I work out the 'bugs' on something like this,
through experience here at home and perhaps a few other friends I know who could
also use it, perhaps it would be worth going the extra mile then.

Certainly, the marketplace is smaller than "every home." But it is a much
easier market to field a product into, as advertising response rates would be
much higher and the places to advertise or get the word out are well known.

Of course, like everything else, the success would depend highly on knowing the
market well and providing the right conveniences at the right prices.

Jon

 

[Spehro Pefhany]

Thanks for the suggestion. I'll look them up. The 5mA is about the limit I'd
want to consider for the MSP430 outputs.

I assume I'll need to re-trigger at each zero-cross? Should I be concerned
enough here to make sure I don't trigger until the AC voltage reaches some
threshold for staying on? Or just re-trigger it in a short burst of pulses long
enough to be sure that's true?

Thanks,
Jon

You can get the zero-voltage crossing kind. Just put 5mA + some margin
through it for "on" and 0mA for off. The optocoupler worries about the
zero crossings.

http://www.fairchildsemi.com/ds/MO/MOC3081-M.pdf




Best regards,
Spehro Pefhany

 

[Adrian Jansen]

My autistic daughter has burned up a few microwave ovens. She loves to cook,
but places the popcorn inside and then presses 3 3 3 and START. Since that is
3:33 minutes and since the popcorn only wants 2 minutes, it often burns horribly
or else bursts into flame.

------------ snipped --------

Have you considered one of the speech recognition chips from
http://www.sensoryinc.com/

Use one keyed only to you and your wifes voice for the activation stuff,
which seems to be the main problem. Of course you still have to deal
with switching mains safely, but that is the easy part, its keeping your
daughter away from possible harmful/dangerous stuff that seems to be the
main issue.

--
Regards,

Adrian Jansen adrianjansen at internode dot on dot net
Design Engineer J & K Micro Systems
Microcomputer solutions for industrial control
Note reply address is invalid, convert address above to machine form.