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'[PIC]: PID Controller For 1Gallon Fish Controller'
2002\06\02@185940 by Ed Edmondson

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Hello All.

I sure could use some help; if there is any to spare?

Thanks a lot for the pointers! But no fishy joked;-(

You haven't seen any PID controlled TEC circuits I could use to keep my 1
gallon Betta fish tank at the same temperature (approximately). I figured I
would also add a turbidity sensor to run for about an hour or two daily to
keep the debris on the bottom from collecting and stagnating the water.

I know this sounds like an over kill but experience is a good teacher. I was
going to measure the water temp and control functions on a 2 X 20 character
display. The sensor would be an LM34/35/AD590 encapsulated

Thanks for the links and advice. If you chime in please be my guest.

Cheers,
Ed



Ed Edmondson, Ph.D.,
1410 West 11th Street
Suite 6
Apt., Colorado 81101-3375
Phone: 719-587-0130
Fax: 719-589-4970
E-mail: spam_OUTee0035jrTakeThisOuTspamaol.com

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2002\06\02@193119 by Scott Dattalo

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On Sun, 2 Jun 2002, Ed Edmondson wrote:

> Hello All.
>
> I sure could use some help; if there is any to spare?
>
> Thanks a lot for the pointers! But no fishy joked;-(
>
> You haven't seen any PID controlled TEC circuits I could use to keep my 1
> gallon Betta fish tank at the same temperature (approximately). I figured I

After dealing with my daughter's 10-gallon tank, I have one solution that
I figured would maintain a perfectly constant temperature: boil the water.
I started with 5 fish and am down to 4 after a couple weeks. The water
turbidity is perfect. And the green sheen looks like a giant bowl of
KoolAid.  I figure it won't be too long that we'll be getting a more
autonomous pet.

Scott

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2002\06\02@211016 by jim korman

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Ed Edmondson wrote:

> Hello All.
>
> I sure could use some help; if there is any to spare?
>
> Thanks a lot for the pointers! But no fishy joked;-(
>
> You haven't seen any PID controlled TEC circuits I could use to keep my 1
> gallon Betta fish tank at the same temperature (approximately). I figured I
> would also add a turbidity sensor to run for about an hour or two daily to
> keep the debris on the bottom from collecting and stagnating the water.
>
> I know this sounds like an over kill but experience is a good teacher. I was
> going to measure the water temp and control functions on a 2 X 20 character
> display. The sensor would be an LM34/35/AD590 encapsulated
>
> Thanks for the links and advice. If you chime in please be my guest.
>
> Cheers,
> Ed
At the rist of going seriously OT.


1. Trying to regulate the temperature of 1 gallon of water is going
to be tough. As long as your room temperature is fairly constant,
about 80F or so, call it good.

2. Bettas don't live in very clean water! Plus they will breath
air by coming to the surface, so there doesn't need to be much
much air in the water.

3. Much better might be to get a 10 gallon tank and divide it
into about 3 partitions and get 3 fish. Use a filter and heater.
Then you'd get to see their "fighting" display.

Good luck, Jim

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2002\06\03@083459 by Roman Black

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Hi Ed, i've built many types of temp control
systems over the years, and PID is probably real
overkill and totally un-needed for a system like
this. Most likely you will be using a standard type
mains AC heater, which is essentially an on/off
device. Add to that the huge thermal lag of your
system, ie time from heater turns on to water temp
actually rises, and you are going to get significant
hysteresis from that anyway.

You will get great results from an on/off system
with high gain, you don't need any deliberate
hysteresis because you have enough in the physical
properties of the heater and water.

Just detect the water temperature, using your sensor
mounted very close to the heater and switch the heater
when temp drops below the setpoint. You will probably
get a few seconds thermal lag anyway, but if not try
and switch the heater with at least 5 seconds on,
if your period is too short you risk element failure
from the continual thermal stresses. It should regulate
within 0.1'C with no probs.
-Roman


Ed Edmondson wrote:

{Quote hidden}

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2002\06\03@120434 by Olin Lathrop

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{Quote hidden}

I agree with Roman.  A long time ago I built a water bath temperature
controller for photographic developing.  I used a fish tank pump to keep the
water circulating and an off the shelf immersion heater as the heating
element.  The kind sold to heat your coffee directly in the cup.  The ciruit
either turned a relay on or off every 64 power line cycles depending on
whether the temperature was above or below the set point.  No hysteresis,
just high open loop gain and a guarantee that the output never got changed
faster than every second.  I used two thermistors in series mounted on
opposite sides of the little tub, and a bridge with a pot to adjust the set
point.

The thing worked fabulously.  Once the set point was reached and it starting
controlling the temperature, I couldn't see any temperature variation on the
photographic thermometer.  Response was surprisingly quick when I dumped in
a liter of cold water or whatever.


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(978) 742-9014, http://www.embedinc.com

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2002\06\05@063052 by Alan B. Pearce

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>Just detect the water temperature, using your sensor
>mounted very close to the heater and switch the heater
>when temp drops below the setpoint. You will probably
>get a few seconds thermal lag anyway, but if not try
>and switch the heater with at least 5 seconds on,
>if your period is too short you risk element failure
>from the continual thermal stresses. It should regulate
>within 0.1'C with no probs.

I used to do this with my spa pool using a CA3059 to read the sensor and
drive a Triac to control the heater. Worked extremely well.

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2002\06\05@073848 by Spehro Pefhany

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At 11:28 AM 6/5/02 +0100, you wrote:

>I used to do this with my spa pool using a CA3059 to read the sensor and
>drive a Triac to control the heater. Worked extremely well.

I'd recommend using a transformer-isolated sensor and isolation between
the load and sensor of some kind. These circuits that run electrically
"hot" sensors, people and water could be a fatal combination. Your setup
was probably okay, but I fear others might not be as careful. At the
least, it should have a GFI on the supply.

Best regards,

Spehro Pefhany --"it's the network..."            "The Journey is the reward"
speffspamKILLspaminterlog.com             Info for manufacturers: http://www.trexon.com
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2002\06\05@080737 by Vasile Surducan

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On Wed, 5 Jun 2002, Spehro Pefhany wrote:

> At 11:28 AM 6/5/02 +0100, you wrote:
>
> >I used to do this with my spa pool using a CA3059 to read the sensor and
> >drive a Triac to control the heater. Worked extremely well.
>
> I'd recommend using a transformer-isolated sensor and isolation between
> the load and sensor of some kind. These circuits that run electrically
> "hot" sensors, people and water could be a fatal combination. Your setup
> was probably okay, but I fear others might not be as careful. At the
> least, it should have a GFI on the supply.
>
 I had used a simply glass test tube like those used for NMR probes, the
sensor inside take a bath in sillicon oil. Command methode was mains pack
alternations, firing by a triac with zero cross detection.
The resistor is earth grounded so no problem untill booom !
The whole driver chip is a 8PDIP TFK U217. But I have doubts your temperature
gradient will be less than 0.1C as someone told here, if extremely high
precautions aren't taken for tank's walls thermal isolation. Recirculating
fluid velocity is also important. I'll go for 0.5C temperature gradient
for 3...4 liters of liquid.
note: thermal gradient is the temperature map difference between various
points of the tank, taken at different levels measured from the bottom.

Vasile

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2002\06\06@035323 by Alan B. Pearce

face picon face
> I'd recommend using a transformer-isolated sensor and isolation between
> the load and sensor of some kind. These circuits that run electrically
> "hot" sensors, people and water could be a fatal combination. Your setup
> was probably okay, but I fear others might not be as careful. At the
> least, it should have a GFI on the supply.

In this case the sensor was encased in a metal tube that was an inherent
part of the heating element, and the whole metal casing was earthed, and was
the only metal piece in contact with the water, so yes it was all OK. But I
do take your point about isolation.

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