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Re: Relay contact ratings.
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could be too

Re: Relay contact ratings.
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Yes, good to hide the chip arch.  But go with a PIC32 (calling all ARM
fans) and you don't have to.

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Is that thermostat for the fridge or for the room?

Either way, easy enough to do with a micro.  I am currently working on
one for the room thermostat.  My wife always complaint that i am
setting the the room temp too high (because the old thermostat reading
is too low).  I got a new one with reading too high, and she is
complainting that i am setting the temp. too low.  I am going to build
one that would fit me right, unless i can find an adjustable temp.
sensor thermostat.  The reading must be 68F, doesn't matter what the
real temp. is.

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NO, NO, NO.  save the world from another junk fridge.

Re: Relay contact ratings.
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Yes, but it strikes me that you much prefer to fix it yourself. BTW, The
PICAXE directly supports the DS18S20 one wire thermometer.

Just thinking further, depending on energy ratings it may be a money
saver to get a new fridge.

--
We have failed to address the fundamental truth that endless growth is
impossible in a finite world.

Re: Relay contact ratings.

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Or just replace the relay with a switch.  Must of these automatic
defrosting fridges defrost so often that they freezer-burn and ruin
your food.
        
                                        ...Jim Thompson
--
| James E.Thompson, CTO                            |    mens     |
| Analog Innovations, Inc.                         |     et      |
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Re: Relay contact ratings.
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It's hard to tell whether it's 'defrosting' an element that is in any
case more or less ice free. The element isn't visible without detaching
the backplate of the freezer, and running the fridge without the
backplate in place would so change the airflow as to make any
observations irrelevant to the normal operation of the fridge.

The reason I got started on this whole exercise was the fact that at
times the bread in the fridge was clearly not frozen, even though the
freezer temperature certainly drops to less than -15C at times. I hadn't
previously looked into the defrost mechanism, and indeed, didn't realise
that there is actually a quite powerful heater element involved. Nor did
I realise that the defrosting occurs every six hours.

A particular issue with the defrost mechanism is that it has a defrost
termination thermostat mounted on the cooling element (set to open at
+11 degrees celsius, closes again at 0C), but regardless of what it
does, the fridge remains in its non-cooling mode for about half an hour
because of the defrost timer. I put a temperature sensor onto the
thermostat, and it shows that the actual temperature there rises to
nearly 20C, presumably because even after the heater is turned off, it's
still very hot.

In addition, there's no link between the defrost timing and the
thermostat. Defrosting may start just as fridge has reached its highest
normal temperature and the termostat is about to turn the compressor on.
So the day to day outcome will vary considerably, even ignoring ambient
temperature changes, making assessing whether the thing is working
properly rather problematic.

Now the bread is probably the thing in the freezer that has the least
thermal inertia. Maybe the fridge has been working correctly (in the
sense of "as designed") all along, and I've just been overreacting to
the occasional thawing of the bread.

I've now learnt stuff about self defrosting fridges that I might have
been happier not knowing.

Sylvia.

Re: Relay contact ratings.
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Though on further examination, by the time you've paid the higher cost
for the chip, the postage from the UK, and either bought or made the
cable, it's considerably cheaper just to buy a programmer from a local
supplier.

http://australia.rs-online.com/web/p/microcontroller-processor/0381582 /

PICAXE is probably good for people who've little or no experience in
programming, particularly at assembler code level.

Sylvia.



Re: Relay contact ratings.
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Get the PICKIT 3 for $7 more, in case you want to program PIC24 or
PIC32.  Not sure if PICKIT 2 can program them.

http://australia.rs-online.com/web/p/microcontroller-processor/6872750/?ori =
gin3D%PSF_392815|acc

Re: Relay contact ratings.
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$7 more than what? The *highest* price I could find for the chip was
about $11 NZ - double that for postage and your still well ahead of a
PICKIT 3. (If you can claim to program a micro-controller in assembly
then don't you already have a programmer that "burns" a chip?)

There are suppliers of PICAXE on both the north and south islands of NZ
and if none of them are any good then they do post - which is what an RS
solution would be. The "programmer" for a PICAXE is *literally* one
resistor which limits current from the RS-232 port to to chip (the chip
will still program at logic levels if you have one of those USB-RS232
converter things).

"Programming" goes like this - You apply 2 to 5.5 volts to the PICAXE
chip. The inbuilt, combined  bootstrap/interpreter automatically runs
and continuously monitors the "serial in" (program) pin. When a valid
signal appears the PICAXE writes the program to flash (and eeprom if you
used that too) and then starts running the program)

There are lots of good reasons not to use a PICAXE.

-Maybe you can't write a fridge temperature control program in just one
thousand line of code.

-Maybe it will take you more attempts than the 10000 times you can
reprogram the thing to get a "bang-bang" controller working.

-Maybe you need more than 28 general purpose byte variables, 256 bytes
of scratch pad RAM and 256 bytes of EEPROM to store the state of the
fridge control algorithm algorithm

-Maybe your algorithm needs more computation power than 8000 multiplies
or divisions per second and the chip isn't up to the job

-Maybe you need more than the 6 I/O pins (you could just use a bigger
PICAXE chip)

-Maybe you need more than 3 x 10 bit ADC's

-Maybe you don't like how the I2C software support allows you to read
temperature directly in one command but only from a Dallas DS18D20

-Maybe you just don't like the English or you pathologically hate any
language called "BASIC" even though it PICAXE BASIC borrows heavily from
bot Java and C++

Whatever it is might be valid, but "price" is a joke.

If anyone can't afford a 9 pin plug and a resistor I will send them one
and for Christmas I will even add a meter of 3 way cable and a plastic
cover for the plug.



Re: Relay contact ratings.
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PICKIT 3 vs. PICKIT 2 is around $7 to $8 more.

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That's what the PICKITs are for.

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I don't think that would be a problem.

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Probably not.


Yes, definitely.  We would need that much ram just for the stack.  We
cannot use the PICAXE.

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May be not, but faster chips are always better, if not too expensive.

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Yes, definitely.  We would need 10 to 15 I/Os.  We cannot use the
PICAXE.

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Yes, probably 4 to 6 ADCs.  We cannot use the PICAXE.

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Yes, we don't want to pay for DS18D20.  25 cents thermistors are good
enough.  We cannot use the PICAXE.

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Yes, I hate BASIC dialect of English.  I only speak C.

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Price is never the issue with useless tools.

We cannot use the PICAXE for any single reason above.  I think we have
more than one.


Re: Relay contact ratings.
On Thu, 15 Dec 2011 13:46:46 -0800 (PST), linnix


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---
Why would you hate BASIC and what do you mean by "dialect of English"?

Run through a good compiler, the object code of any programming
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Re: Relay contact ratings.
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BASIC force me to think differently with

reg &3D% ~BIT5;
reg |3D% BIT7 | BIT 4 | BIT 2;
reg >>3D% 4;

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Re: Relay contact ratings.
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Ah. Got you. And (IIRC) you are correct that a PICKIT 2 won't do PIC24.

My response was in regard to SE's aims for a fridge controller. I don't
know what your requirement was.
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SE said in a post that she can program in assembler. I make the
assumption that she is talking about a micro-controller because that is
the context of the thread.

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Un-needed for SE if she use's a PICAXE




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For a bang-bang controller of a domestic refrigerator (SE's case)?
PICAXE is in BASIC. What the user can access is for their exclusive use.
The system manges it own stack from separate RAM.

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8000 operations is not enough for SE's case?
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Ah - You can't use PICAXE-08M2. Yo might be able to use PICAXE-20M2. You
could use PICAXE-28X2, PICAXE-40X2. They are starting to be expensive,
but for a one off, if you don't have a set of tools and a programmer
already at hand, still worth a look

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You could use PICAXE-28X2, PICAXE-40X2.

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The PICAXE also implements plain vanilla 10-bit ADC's. If you want to
use a thermistor or just about anything else you can interface to a
micro-controller you can. If your an absolute Scrooge and don't care
about absolute accuracy you could even use the readinternaltemp command;
the hardware for that is free!

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Doesn't that make love letters to that special someone difficult to read?

Does it require many #PRAGMA's before you can link up?

-----------------------

One thing that amazes me is that BASIC is often blasted because it is
easy to produce unstructured code and has that horrible "GOTO"
statement. But C is a great language - you just have to put in lots of
effort to produce properly structured code and not use the built in
"Goto" command.

Mind you, I do have a bad attitude to C. In uni I mastered Fortran, 8080
(and Z80), 6502, Pascal (I faked my way through Pascal, it just wasn't
interesting to me and I couldn't run it at home - thank goodness
commenting and analysing the algorithms was important), FORTH and even
edlin! - very useful stuff, they didn't even tell us we could type in
our name as a command and be amazed and entertained by the resulting
chaos. In the last few weeks of the last programming class one of the
fellow students asked which language they should specialise in to get a
job and they were told "C"!!!  (followed by loud expletives from the class)

---------------------------------

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This is a useful tool, particularly for one off's with simple
requirements. For someone already set up and experienced with another
processor maybe not so useful. It did seem that SE didn't have that
(since she mentioned buying a programmer)

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Re: Relay contact ratings.
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I am also trying to rebuild my busted fridge, with a more intelligent
defrost controller.  I don't know if you are following the other
discussions.  We are trying to measure the compressor efficiency and
temperature difference, in order to minimize heating and cooling
cycles.  To do so, we need to have several thermistors readings and to
keep track of past operating cycles.  At a minimum, the user would
need to be able to set the fridge target temperature, as well as other
operating parameters.  I don't think the PICAXE is sufficient for
this.

Re: Relay contact ratings.
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power,
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http://australia.rs-online.com/web/p/electromechanical-relays/1279550 /
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Ah no, I wasn't following it all - you know a PICAXE can also send RS232
to a laptop .. (duck and run)


Re: Relay contact ratings.
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So can PIC32, or even WiFi via USB.  In fact, we might end up tying
all these appliances to a PC.  The most efficient defrosting is to
pipe hot air or water from natural gas burners.  So, we need to
control many home appliances altogether. However, installation is more
complicated.

Re: Relay contact ratings.
On Thu, 15 Dec 2011 10:22:50 +1100, Sylvia Else
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---
Did you see my posts re. a hardware solution here and on abse?

--
JF

Re: Relay contact ratings.
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I did, but I've formed the view that if I were going to do this, I'd
include the thermostat as well, and choose a better point in the
thermostat hysteresis at which to start the defrost cycle, rather than
having a random relationship as is the situation now.

Sylvia.

Re: Relay contact ratings.
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Yes, we should have a thermistor for the room temperature, one for the
inside temperature, one at the beginning of the heat exchanger and one
at the end.  This way, we can measure the temperature gradient based
on compressor and heater run time, and control them.  This should
reduce unnecessary heating and cooling cycles.

Re: Relay contact ratings.
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The US Department of Energy sponsored research into improving
refrigerator efficiency.  Here are a couple of starter links:
http://www.ornl.gov/info/ornlreview/rev28_2/text/fri.htm
http://www.ornl.gov/info/press_releases/get_press_release.cfm?ReleaseNumber =
3D%mr19970501-00

The main thing was increasing insulation from 1/2" to 2".  Adaptive
defrost is mentioned too (in the 2nd link).

The ultimate in efficient refrigerators is a chest freezer, home-
converted into a fridge.
http://mtbest.net/chest_fridge.html

--
Cheers,
James Arthur

Re: Relay contact ratings.
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s_releases/get_press_release.cfm?Release...
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Yes, that's exactly what i am thinking about.

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Or a regular fridge turned sideway, with door pointing up.


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