# H2O Auto-Fill Schematic Sanity Check

#### Fish4Fun

##### So long, and Thanks for all the Fish!
Aug 27, 2013
471
Before I start building this I was hoping for a quick sanity check....The purpose of the circuit is to Auto-Fill a 250 gallon water tank we use @ my business to supply water to our live bait tanks. The water is used throughout the day and is supplied to the 250g tank from a well. Because well water has little to no dissolved Oxygen it must spend some period of time aerating prior to being used, so it is typically filled just prior to store closing, or at least in theory it is suppose to be filled just prior to closing....but employees sometimes forget....So rather than waste effort fussing at employees, I thought I would simply automate the system....

Code:
Logic:
Logic:

|  Sensors  |  | Solenoid |
|  Top  | Bottom |  Dark  |  Relay  |  State  |
|--------|--------|---------|---------|----------|
|  |  |  |  |  |
|  OFF  |  X  |  X  |  X  |  OFF  |
|  |  |  |  |  |
|--------|--------|---------|---------|----------|
|  |  |  |  |  |
|  On  |  Off  |  Off  |  Off  |  OFF  |
|  |  |  |  |  |
|--------|--------|---------|---------|----------|
|  |  |  |  |  |
|  On  |  On  |  X  | -> On  | -> On  |
|  |  |  |  |  |
|--------|--------|---------|---------|----------|
|  |  |  |  |  |
|  On  |  Off  |  On  | -> On  | -> On  |
|  |  |  |  |  |
|--------|--------|---------|---------|----------|
|  |  |  |  |  |
|  On  |  X  |  X  |  On  |  On  |
|  |  |  |  |  |
|--------|--------|---------|---------|----------|

As the logic table shows, once the fill cycle starts, it continues to fill until the Top Switch is disengaged. The On Cycle can be triggered ONLY when the water level is below the Top Switch. If the level is below the top switch and it gets dark, then the fill cycle should begin....if the level drops below the bottom switch then the cycle should begin.

Here is the schematic:

There are two basic Dark Detector Circuits common on the WEB, the one used in the schematic, and a second one that uses a second BC547 transistor....I have no experience with Dark Sensors, so any experience-based thoughts here would be appreciated. The SPDT Relay I plan to use is fairly low current (~85mA @ 12V), the Water Solenoid consumes ~190mA, but the transistor only has to supply the current for the relay, the relay will then engage the Solenoid and supply itself until the Top Switch is turned off.

I am fairly confident this will work, but I would really appreciate a sanity check....

Fish

Note to Site Admin: Having a variable point font for <Code Tags> really takes all of the fun out of Ascii tables/art....even if I set the font to Courier, the paste function transforms the white space to tabs....is there really a good reason for this? I am not sure about the current forum SW of the day, but in the old VBull SW you had to intentionally enable this type of counter-intuitive behavior....What is the purpose of <Code Tags> if not to allow the user control of white space?

#### Fish4Fun

##### So long, and Thanks for all the Fish!
Aug 27, 2013
471
Here is an image of the logic table, lol.

I really would love to know if there is a work-around for the <code tag> issue.....seems kinda silly to have to post an image in place of a simple text file.

Fish

#### Arouse1973

Dec 18, 2013
5,177
Hi Fish

I personally would have a threshold detector of some kind for the light sensor so the output switches fast and clean. You will find because it gets dark over quite a long period of time that the transistor will spend an amount of time in it's linear region and thus start to heat up.

I don't quite understand the switching circuit, when the top switch is closed and it's dark where does the relay get it's power from? I might not understand the requirements correctly.

Thanks

#### Fish4Fun

##### So long, and Thanks for all the Fish!
Aug 27, 2013
471
As an Addendum.....It turns out I don't actually have any BC547 transistors on-hand....I tried an 2N3904 and it didn't work well enough to satisfy me.......I really haven't done much with BJTs...long history of failures there....lol....there is absolutely nothing critical in this circuit except that it work, so I replaced the transistor with an IRFSL23N20D (bought a ton on a surplus deal back a million years ago), it is WAY overkill for the purpose rated @ 200V, 24A with an RDSon of 100mOhms.....fast rise and fall times, etc, etc....absolutely nothing about it says, "Put me in a 12V circuit to power an 80mA relay".....LMFAO, but it was the first thing I grabbed.....Circuit works just fine....but way too fast...so I added a 1000uF capacitor between the gate and ground.....turn-on takes ~5 minutes...I would like to increase the delay to something over an hour, but I can't see dedicating that much capacitance to this project....it would be cheaper to simply add a uController....(I am worried that leakage might over take charging)....so I will live with ~5minutes for now....fiddle with it later if I am not happy with the 5 minute delay...

I personally would have a threshold detector of some kind for the light sensor so the output switches fast and clean.

Obviously I am going the other direction.....I am exploiting the linear region to increase delay....If this To-220 case heats up while in the linear region with a 275 ohm DCR relay as it's only load then it will just have to get hot, lol....I think it is safe to assume the To-220 can handle the worst-case power dissipation of 524mW without too much worry about a heat-sink

I don't quite understand the switching circuit, when the top switch is closed and it's dark where does the relay get it's power from? I might not understand the requirements correctly.

The idea is that the circuit remains un-powered when the tank is full (ie: Top Switch = "Open")....Once the top switch opens the circuit is left open until the top switch again closes....There is never a need to fill the tank when it is already full, nor any reason to monitor it.....

Once the water level drops below the Top Switch, the circuit is enabled until one of two things happens:

1) It gets dark and stays dark for at least 5 minutes......

2) The level drops below the bottom switch.....

In either case, once the circuit is enabled it runs until the Top switch is once again switched off.

In the case of extreme cloud cover it is quite likely the tank will fill during normal business hours, but to be fair, it will also likely be raining and it is improbable there will be much demand for water to fill minnow buckets....

The other "saving grace" is that we rarely use more than ~1/4 a tank in any given day...frequently we can go a week w/o filling the tank, but this is also part of the problem....employees forget to check it before they close, and then in the morning, when minnow sales are at a peak, there isn't any aerated water and the finger pointing, pissing and moaning starts....So, if it automatically re-fills every evening after dark then all is good and there is one less thing to worry about, lol.

That being said, what I don't need is the circuit responding to every cloud, bird and butterfly thus filling the tank with un-aerated water in the middle of the day...wouldn't even hurt if the Full moon prevented it from engaging for some portion of the night....or even a couple of nights in most cases.....but I am hoping that the five-minute delay will eliminate 98% of the "false trips", and that the tank will be full enough when there is a "false trip" that the un-aerated water will be a small percentage of the tank volume....Assuming a cloudy, dark day does trip it, if it were filled the night before then it is unlikely there will be more than 10 gallons missing, and 10 gallons of un-aerated water is only 4% of the total volume.....not enough to worry about.....The problem is having 200 gallons of un-aerated water.

Thanks for the Response! Hope the explanations weren't too much, lol.

Fish

#### Arouse1973

Dec 18, 2013
5,177
Hi Fish, yeah I got the principle from your first post. I was after an explanation on how the circuit worked.
Cheers

#### Arouse1973

Dec 18, 2013
5,177
I have re-drawn the circuit so my pea sized brain can try and understand it. Does this look correct Fish?

#### Fish4Fun

##### So long, and Thanks for all the Fish!
Aug 27, 2013
471
One final change...went to a 10000uF Capacitor on the mosfet gate and a 510k pull-up resistor...this increased the turn-on delay time to slightly over 30 minutes.....Surprisingly the mosfet does exhibit some temperature rise during the final 5 minutes before turn-on, but it is certainly not enough to worry about....perhaps 1C...just enough that you can feel the difference between it and one next to it that isn't connected to anything....I would guess that the actual turn-on time will deviate slightly with respect to ambient air temperature for several reasons, but it is absolutely inconsequential to the circuit's function....a 30 minute analog electronic timer is problematic under any circumstances, lol. I will say watching the gate voltage rise on the DSO is about as interesting as watching paint dry.....

Here is the schematic as currently employed:

Again, Thanks!

Fish

#### Arouse1973

Dec 18, 2013
5,177
That looks better, I thought there was something odd about your first circuit. So now you have latched the relay so even if it gets light after the dark switch has triggered. It won't stop filling until the water level breaks the full switch.

#### Fish4Fun

##### So long, and Thanks for all the Fish!
Aug 27, 2013
471

Yes, Sorry, posted before refreshing.....Looking @ my first schematic I think my dyslexia out paced my A.D.D. meds......My problem is that once I "have it right in my head" I tend to "mentally correct what is actually on paper" and absolutely fail to see the errors on paper unless I start again from scratch....makes it really frustrating on both sides when people are looking at things I have drawn/designed and seeing what is really there while I am seeing something quite different, lol. You have helped me many times....Thank You....but I would urge you be a little less gentle when I am obviously on a different page.... a difficult ask, I know....but when you look at something as flawed as the first schematic, don't be afraid to be direct.... I am not just thick-headed, but also thick-skinned ;-)

Again, THANKS!

Fish

#### Arouse1973

Dec 18, 2013
5,177

Yes, Sorry, posted before refreshing.....Looking @ my first schematic I think my dyslexia out paced my A.D.D. meds......My problem is that once I "have it right in my head" I tend to "mentally correct what is actually on paper" and absolutely fail to see the errors on paper unless I start again from scratch....makes it really frustrating on both sides when people are looking at things I have drawn/designed and seeing what is really there while I am seeing something quite different, lol. You have helped me many times....Thank You....but I would urge you be a little less gentle when I am obviously on a different page.... a difficult ask, I know....but when you look at something as flawed as the first schematic, don't be afraid to be direct.... I am not just thick-headed, but also thick-skinned ;-)

Again, THANKS!

Fish

Hi Fish. I could have said what a load of shite, this won't work. But that doesn't help anyone, this is why I prefer to say something like, can you explain how your circuit works. This is really urging them to have another look and follow it through.

We all make mistakes I have been doing this for over 20 years and yep I still forget to turn the power supply on and wonder why my circuits not working.

I am the same as you, it's all in my head. For simple circuits I very rarely draw a circuit diagram, just a few datasheets and I am off. I then forget what I did and have to look at the PCB I have made.

I like helping people, I get a great deal of pleasure from it. Especially if someone is grateful, like yourself. But I don't have time for lazy bastards how just want you to spend your whole evening looking for a data sheet for them.

All the best

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