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PostPosted: Jan 12th, '12, 16:37 
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with temperature the voltage across the diode changes, so adding extra wire will add resistance...
Maybe you could make 5 identical probes.. but then you still have the variation in diode batches to account for...
Maybe you could make all the probes, put them all in a glass of water + ice and send the "calibrate 0deg" command :D

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PostPosted: Jan 12th, '12, 17:53 
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Yeah it's almost certainly that, haven't had chance to check it further.
28ohms in each direction, crap cable, obviously, because it's not _that_ long.

SuperVeg wrote:
Maybe you could make all the probes, put them all in a glass of water + ice and send the "calibrate 0deg" command :D

Is exactly what needs to be done ;)

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PostPosted: Jan 13th, '12, 11:44 
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You might need some 120mm2 cable to run the power out that far :P

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PostPosted: Jan 14th, '12, 16:42 
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Small update.
Made a second probe on a long piece of wire (some decent wire this time, 1.4 ohms in each direction)
Froze them solid in a cup of icy water.
Took them out and plugged them in, one at 99 counts one at 100, looking good.

I have taken the pot out, it had drifted by over 100 ohms since I started this thread, trimming out 0V increases your resolution slightly, but if the pot drifts it screws the result up, better lower resolution (not much) than a drifting pot.

The point BW raised about ice being less than 0C when it comes out of the freezer, doesn't seem to happen.
It sat there at 100 counts for a long time, 20 minutes perhaps then started climbing slowly.
Looking at the block of ice I could see little melt holes around the wires in the ice, even the wires warm enough to melt the ice around them.
I think that as soon as current flows through the diode, it warms and melts the ice but as there is a block of ice surrounding it, it stays at 0.0000000001 degrees C (approximately)
That's my theory anyway.

Both devices have warmed to room temperature and are both reading the same within 1 or 2 counts (~0.6C)
The multiplication factor is the same between channels, showing that the amp stages are consistent, as is the mV/degree of the diodes, which is expected, but nice when it happens :)

Tripped up a couple of times on this project, but overall I am very pleased with the results.

I also had a thought that temp sensors in the water, could also be used as backup level sensors (assuming the water temp is different from the air temp - in a big system, it should be)
If the water level dropped below the level of the sensor the temp would change rapidly to equal the air temp...

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PostPosted: Jan 14th, '12, 17:29 
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Agreed on the temp of the ice point. Freezers often go down to around -18 deg (fridge ones)
Thats why i sugested adding water to a cup of ice, but it seems to quickly heat up to 0deg once you take it out and provide some electrons :) Just for the sake of curiosity can you do a test with it still in the freezer ? Actually being in a block of ice, maybe the ice would actually insulate the diode somewhat from the lower air temp of the freezer compartment... anyway, its kinda irrelavent i guess.

What kind of pot where you using? one of those large ones with wire tabs or the smaller through hole pcb mount ones ?

Great project DuiNui, hopefully one day I will finish off my priority projects and start playing with some AP based electronics :)
I'm hoping to get something general purpose sorted out and do a run of proper PCBs for anyone interested...

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PostPosted: Jan 14th, '12, 17:53 
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SuperVeg wrote:
Just for the sake of curiosity can you do a test with it still in the freezer ?

Good idea, I know the temp inside the freezer is less than 0C, if the device continues to read zero in the freezer, it gives my theory some credibility !

SuperVeg wrote:
What kind of pot where you using? one of those large ones with wire tabs or the smaller through hole pcb mount ones ?

PCB type, was in a box of a bunch of stuff I brought back from the UK last time I was there, would be at least 20 years old, which might explain the drift.

SuperVeg wrote:
Great project DuiNui, hopefully one day I will finish off my priority projects and start playing with some AP based electronics :)

Thanks :)
There does come a point with the FT/GB side of things when it just seems to run itself and you either start planning serious expansions, and/or you add some electronics to make it more reliable.
From reading 100's of threads over the last few years, the 2 main HSM's seem to be:
1) Pumping the sump/FT dry.
2) Leaving the top up hose in the FT and going to make a bacon sarnie.
Both of those scenarios are easily prevented with some very simple electronics.


SuperVeg wrote:
I'm hoping to get something general purpose sorted out and do a run of proper PCBs for anyone interested...

The reason (other than 'cos I like to play) I started with the electronics on this was in my last system I miscalculated the sump size, there wasn't enough water to fill all 3 GB's at once, so I made a 0 pressure indexer which worked really well.
Constant Flood seems to be this year's black, so I haven't put any more effort into that.
Having said that, both my Papya died from root rot, so when I expand I may make 2 or 3 GB's micro controlled (in terms of water in and water out valves)
Gives me complete control of how much water is in any part of the system and for how long.

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PostPosted: Jan 14th, '12, 23:49 
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I like electronics.
But I don't like electronics AP. I think electronics should kept minimum in AP.
Better focus on strategy to make good system, the strategy should make system simple, than make it unnecessary complex.


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PostPosted: Jan 15th, '12, 02:32 
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Ao+ wrote:
I like electronics.
But I don't like electronics AP. I think electronics should kept minimum in AP.
Better focus on strategy to make good system, the strategy should make system simple, than make it unnecessary complex.


I agree, to a point.
But if a simple level sensor saves your fish, this is not a complication, but a system saver.
Solid state electronics are more reliable than any pump or electro-mechanical device.
If adding an extra safeguard prevents losing your fish, I'm all for that.

We've all had hsm's we wish we hadn't :)

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PostPosted: Jan 15th, '12, 04:01 
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I feel that sensor is most difficult part. Mocro is easiest. Actuator is moderate.

difficulty in sensor and actuator lead to unreliable system, if we use it as repetitive main function(like close open valve for F&D, or control FT water level)

But I agree with you if we use as additional safety equipment such as alarm for unsafe condition.
And timer,electronic is the best way. Maybe you should focus on timer rather than temp sensor.

I have plan to design Timer also
I'll try AVR. Main feature shold be Timer, data loger, usb interface, some IOs. This is big project already.


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PostPosted: Jan 15th, '12, 05:09 
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The only reason electronics may be unreliable is due to bad design.
Thats the fun of being the designer trying to consider all possible scenarios, and incorporating correct design inputs and protection mechanisms to make it reliable.
Sure its possible for a part to fail while operating within its limits, however this is actually quite rare. The biggest cause of part failure is operation outside its limits, and that is always due to bad design. Voltage surges, lightening, static, moisture, overload etc if any of these cause the circuit to fail, its the designers fault for not protecting against it :D
And thats why its fun :wave:

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PostPosted: Jan 15th, '12, 11:23 
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Ao+ wrote:
Maybe you should focus on timer rather than temp sensor.

That was too easy, took less than a day from scratch :)

Most of the time spent on the Temp sensor was trying to calibrate it accurately without an accurate/linear thermometer to calibrate it with.
I still haven't got round to buying a decent one
*adds that to list of things to buy today*

It's easy to make safety critical* stuff reliable you need multiple ways to make a decision.
In a 4 engine aircraft there are a total of 32 "computers" running on 4 "lanes" that control and monitor the engines, all running the same software, all making prioritized votes on safety critical decisions, this is overkill for AP but I think you know what I mean ;)

If you want ultra reliability you have at least 2 ways of making a decision and at least 2 ways of making that decision happen, independent of one another.

So you have 2 sensors in the FT to see if the water level has become critically low, then you have 2 separate ways to turn the pump off.
Ideally you want 2 micros running independently, but again probably overkill for AP.
That way you need a simultaneous failure of 2 parts of the system for it to fail.

*I use the term safety critical here from the point of view of the fish and or pump, not human safety.

Properly designed and implemented, it costs a perhaps 10's of dollars and is ultra reliable and could save hundreds of dollars in fish

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PostPosted: Jan 15th, '12, 13:33 
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SuperVeg wrote:

And thats why its fun :wave:


LOL :laughing3:

Dui you said "overkill" that the point.

When i was student my teacher told me not to rely on only overload current to protect a motor, better to have under current sensor because it cause the over current.

Is it better to have large volume of water, design large system, to prevent temp fluctuation and has just a thermometer in system?
Is it better to do CHIFT PIST than put pump in FT and have water level sensor?
My point is if one expert in hammer he has tendency to solve every problem by hitting. The expert trap. I used to do like that. :D

BTW I think timer is not that easy. Timer for micro is just xtal and a few lines of code.
But timer for human need to have
-human interface LCD+buttons and/or USB+driver to edit on/off time.
-Driver/relay to on off pump,aerator ,feeder, ect.
- May be some sensor port
I propose to make the timer as a general AP control unit.I will do it also, we can share some idea. What do yo think?


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PostPosted: Jan 15th, '12, 13:57 
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I said "overkill" for a fully dual redundant system, but actually it's still only a few dollars.
I think that no matter how well a system is designed, you always get the unexpected one day.
The bottom line is:
You want to make sure your fish have water no matter what else happens in the system.
It is reasonably easy to achieve at very low cost with a micro.

About the Temp sensor, in TL we are lucky with the weather.
Never seen it lower than 13C or higher than 43C (in Chiang Mai)
In the UK it's -10C to 35+C, now if it was -10C you will want to disable your auto-feeder, for example.
Temp sensor in TL is fairly useless apart from the fun factor, but in the UK and many other places, it might save a tank full of dead fish due to over feeding.
Just an example.

About idea sharing, of course that is a very good idea, and what forums are all about :)

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PostPosted: Jan 15th, '12, 14:09 
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Yeah you may be right.
Some body said, because Thailand locate in good weather condition so we don't prepare for future. Unlike Farang or China they face cruel winter they must think longer to the future.


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PostPosted: Jan 19th, '12, 19:03 
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Well, I relented today.
Had to go into town anyway so stopped off at the electronics shop and bought some LM35's and other stuff.
The thing that was driving me mad was not knowing for sure whether the diode measurement was accurate and or linear.
This (as I've said before) comes from not knowing if my household thermos are actually accurate, they all show different values at freezing, room temp and boiling.
It was good to see that the diode was within 0.5C of the LM35 and was linear across the temps I tested it at.
They were 60Baht each though (2USD) so while not a lot of cash, considerably more expensive than a diode, the big big bonus (as KP pointed out) is that they are factory calibrated.
You still have to calibrate the amplifier stages but it is a lot easier when you have a known guaranteed mV/C ratio (in the case of the LM35 10mV/C)
The diode is easily as accurate as the LM35, but you do need a good quality thermo to calibrate it with !

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