# I need to hire someone for a logic design

Sep 25, 2014
73
I'm building a project that will require at least one, and maybe two, automated processes involving logic circuits and a DC power source (with a wall wart) with a battery backup. It(they) will be simple, but are beyond my capabilities. If anyone is interested, PM me. Thanks.

#### (*steve*)

##### ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd
Moderator
Jan 21, 2010
25,510
Any reason you can't post it here? You may get much of the help you require free.

Sep 25, 2014
73
I guess I could. I'm such a n00b with logic circuits that tackling it myself seems daunting. But maybe it's possible. I'll get the specs together.

#### (*steve*)

##### ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd
Moderator
Jan 21, 2010
25,510
Ok, start with a general explanation of what you're trying to do and avoid the temptation to create a huge post at first.

Sep 25, 2014
73
That would be great if someone could help me here. I'm creating an awesome aquarium setup. I took a little while in proceeding with this thread because I wanted to make sure I had my needs well thought out. I need to have two electrodes that, when in contact with a bubble in the aquarium, will activate an AC power source. The electrodes should be adjustable so that varying current can be sent through. The length of time that the AC power source is active should also be controlled. There will be a refractory period (fixed, though adjustable would be nice if not too much extra design) before the AC power source is activated again. Ideally, this will NOT involve a PC, and will be pretty simple. If it could run off a few D cells, that would be great. thanks.

#### davenn

Moderator
Sep 5, 2009
14,300
I'm creating an awesome aquarium setup.

OK

. I need to have two electrodes that, when in contact with a bubble in the aquarium, will activate an AC power source.

cant really make sense of that

The length of time that the AC power source is active should also be controlled

what sort of AC power source ? voltage ? what is it supposed to power ?

There will be a refractory period

a what ??
doesn't make sense

OK, explain in a little more and clearer detail, what this project is supposed to achieve

cheers
Dave

Sep 25, 2014
73
It's supposed to turn on devices related to a "protein skimmer". That part isn't really important. I just need to have an AC jack energized so that it provides power to the devices plugged into it. As for the bubble and the electrodes, a current is to flow from one electrode to another. However, it won't because of a break in the circuit. The circuit is then closed when the gap between the electrodes is bridged by foam (bubbles).

#### hevans1944

##### Hop - AC8NS
Jun 21, 2012
4,891
@Madsalts : I read some of your previous posts dating back to when you joined this forum in September 2014. I even responded to one of them to confirm a PWM controller would not harm your motor if set to 0% duty cycle. It appeared then that you have some interest in electricity, motors in particular, but very little understanding of electricity or electronics. That's okay. We were all beginners once upon a time. Hopefully you have climbed the learning curve a bit more since then.

You need to learn how to describe a problem, instead of describing a "solution" that may or may not be satisfactory. For example, you say you are designing "an awesome aquarium setup" but provide no information on exactly what that entails. I have owned several fresh-water aquariums and once thought about building a salt-water aquarium (but gave that up because of the complexity). Things that I noticed that make for an "awesome" aquarium include size (bigger is better) and compatible aquarium stock (more variety is better). It has never impressed me that lighting, aerators, automatic fish feeders, or automatic cleaners added anything to the experience of watching the aquatic life do their thing. In fact, I find it best if those things go unnoticed. Which brings us to bubbles.

Bubbles are simply volumes of gas in a liquid medium, or in the case of an aquarium, water. It is the nature of bubbles in water to rise quickly to the surface and quickly dissipate as the gas is released into the atmosphere. It is virtually impossible prevent this from happening, even if the gas forming the bubble is applied very slowly through a small orifice at minimal differential pressure between the gas inside the bubble and surrounding water pressure, which pressure is of course a function of depth. A bubble in water is never in equilibrium with the water surrounding it... unless the "bubble" is a closed, sealed, container like a Cartesian Diver toy.

Are you trying to create a static bubble that remains attached to the gas supply orifice, perhaps detaching it after it reaches a certain size? Why do you think there will be any significant conductivity between two electrodes inserted in the bubble, assuming the bubbles are formed with a dry gas? Or is it your intent that the two electrodes make contact with the outside of the bubble, which is essentially contact with the water surrounding the bubble? How are your bubbles formed and what are you trying to do with those bubbles?

And why does it depend on activating an AC power source? Why would you want to send a varying current through the two electrodes? Are you aware this will cause local electrolysis at the electrodes, releasing ions that will probably be detrimental to the aquarium population?

#### (*steve*)

##### ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd
Moderator
Jan 21, 2010
25,510
Yes, as I warned you against, you have given us a proposed solution.

What I wanted was something along the lines of "I want to turn on a pump when foam is detected in the tank".

#### CDRIVE

##### Hauling 10' pipe on a Trek Shift3
May 8, 2012
4,960
Hey Hop, I read this twice.
https://en.wikipedia.org/wiki/Cartesian_diver
Later, I'm going to a Christmas party at the hospital I used to contract for. I'm going to drink copiously and read it again. I think my reading comprehension will increase exponentially by then. Wish me luck!

Chris

#### BobK

Jan 5, 2010
7,682
It's really pretty simple nephew Chris (since Bob is your uncle, and Martin's great uncle.)

You have container open at the bottom a mixture of air and water in it. The air will be at the top. The mixture is just enough to make it float to the top under normal pressure. The container is in a sealed plastic bottle like a 2 liter coke bottle filled with water. If you then squeeze the bottle, the pressure will increase, which decreases the volume of air in the diver, allowing more water in. Now the diver is heavier and sinks. Release the pressure and the air expands and the diver floats to the top.

Bob

#### Martaine2005

May 12, 2015
4,965
I'm going to a Christmas party at the hospital
Uncle Chris,
Wow, on tap too....I mean drip! Obviously not a regulated drip?
Taking grapes to hospital has a different meaning now!
Have fun, and wish the OTHERS a merry xmas....

Marty

#### Martaine2005

May 12, 2015
4,965
It's really pretty simple nephew Chris (since Bob is your uncle, and Martin's great uncle.)
Haha Bob,
Does that make you my Great Great Great Uncle?
I prefer Fanny, my Aunt

Martin

Sep 25, 2014
73
I'll take this from the top.

I am setting up a saltwater aquarium. The water in which the fish live must have a certain concentration of “dissolved organic content”. With too little “dissolved organic content”, nutritional requirements of plants will not be met. With too much, the health of other organisms within the tank will be compromised. There is a very broad range of tolerance that is acceptable to the inhabitants of the aquarium, both plant and animal. However, there is a range of concentrations of “dissolved organic content” that is optimal. A very common method, if not the most common method of ensuring that concentrations of “dissolved organic content” do not become too high is to route water from the aquarium to a "protein skimmer"*.

Water within the aquarium is aerated. With greater concentrations of “dissolved organic content”, bubbles formed at the surface as a result of aeration will linger longer. All else being equal, a longer length of time for which a bubble exists on the water surface correlates positively to a greater concentration of “dissolved organic content” within the water.

From past experience, I know that bubbles form on the surface of the water at only one end of the aquarium, where there is surface disturbance created by an aeration device. Only under conditions in which the “dissolved organic content” is too high do the bubbles travel across the surface of the water to the far side of the aquarium.

I would like to have an electrode positioned under the surface of the water at the far side of the aquarium (away from the aeration device). I would like to have a second electrode positioned about 2 cm above the surface of the water nearby (also at the far side of the aquarium). When a bubble drifts into contact with the electrode positioned above the surface of the water, a path will be formed through which a current can travel from one electrode to the other. The current path will be from one electrode, across the surface of a bubble, through the air/water interface, through the water in the aquarium, to the other electrode.

When current travels from one electrode to another, a circuit is closed, and a pump must turn on. The pump will move water from the main tank of the aquarium into a protein skimmer. The pump is powered by AC current from wall mains. Therefore, the pump will be on when the AC jack into which it’s plugged is energized. I want to control whether the AC jack is energized or not as a function of whether or not current flows between the two aforementioned electrodes.

Ideally, the amount of current provided by the cathode should be adjustable. This is so sufficient current is generated to close the circuit, but not so much as to risk the health of aquarium inhabitants.

Two parameters related to the AC jack must be controllable as well. First, when the AC jack is energized, the length of time for which it is energized should be adjustable. Second, after the AC jack has been energized and then becomes de-energized, there must be a period of time during which the jack will not become energized again, even if the circuit involving the electrodes in the aquarium is closed again. This length of time during which the AC jack will not become energized after having been energized once should be adjustable.

Any device built to accomplish the above should be simple and use commonly available DC cells (i.e, AA, C, D).

* A description of protein skimmers can be found at: http://reefkeeping.com/issues/2002-06/fm/feature/index.php

#### davenn

Moderator
Sep 5, 2009
14,300
When current travels from one electrode to another, a circuit is closed, and a pump must turn on. The pump will move water from the main tank of the aquarium into a protein skimmer. The pump is powered by AC current from wall mains. Therefore, the pump will be on when the AC jack into which it’s plugged is energized. I want to control whether the AC jack is energized or not as a function of whether or not current flows between the two aforementioned electrodes.

Ideally, the amount of current provided by the cathode should be adjustable. This is so sufficient current is generated to close the circuit, but not so much as to risk the health of aquarium inhabitants.

firstly
I hope/assume realise that you CANNOT take open mains voltage anywhere near the water
so a secondary lower voltage powered controller circuit is required
as with your suggested D cells etc

secondly
I see a huge problem trying to get consistent operation using the bubbles as conductors
Because the bubbles will have a brief life, a couple of seconds or less, the control circuit
is going to be continuously spluttering on and off between the bubble positioning between the electrodes

maybe that could be overcome by an initial triggered switch on and then let the controller keep the pump on for a set time
... 10 mins ... 20 mins whatever

Dave

#### BobK

Jan 5, 2010
7,682
maybe that could be overcome by an initial triggered switch on and then let the controller keep the pump on for a set time
... 10 mins ... 20 mins whatever
Dave
Dave,

That is exactly what he suggested in his post. As well a low voltage supply for the logic (batteries.) He also want a set off period after each on period.

Bob

#### (*steve*)

##### ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd
Moderator
Jan 21, 2010
25,510
I would recommend that an AC signal be used to prevent the electrodes from being eaten away or otherwise contaminated.

I have seen a circuit which uses this to detect the water level in a tank. I see no reason why it could not be used to detect a bubble -- presuming the bubble is sufficiently conductive.

I'll try to find the circuit...

Aaah -- that was too easy... http://www.electroschematics.com/6653/simple-water-detector-circuit/

This *might* detect a bubble. You would also need to extend the duration of the pulse to power the pump for the required duration.

I recall a fairly simple circuit using one of the CMOS counters which would run until disabled by a particular output bit going high. The circuit would be re-triggered by a reset pulse. I can't find that anywhere though :-(

Sep 25, 2014
73
Thanks Steve. Using the circuit to detect water levels seems like another great application. If the mentioned circuit can't detect a bubble, is there a way to modify it so that it does? Increase the voltage, maybe?

I would recommend that an AC signal be used to prevent the electrodes from being eaten away or otherwise contaminated.

Help me follow the reasoning here. From studying electrochemistry in high school, a DC current will, under some circumstances, be eaten away or collect crystals at either the anode or cathode (I can't remember which). By using an AC current, each electrode switches between being a cathode and anode. This would slow eating away/deposition of crystals by roughly half, but still not prevent either of these effects (correct?). Also, why would there be a problem with eating away/deposition of crystals at all? If there is current flowing under very limited circumstances, wouldn't the electrodes remain more-or-less electrically inert (especially if stainless steel were used)?

#### (*steve*)

##### ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd
Moderator
Jan 21, 2010
25,510
If the mentioned circuit can't detect a bubble, is there a way to modify it so that it does?

Not sure. I'd probably start with a multimeter in the ohms range with one probe tip dipped in the water and the other touching the bubbles. See if it detects a resistance rather than just displaying OL. If it does, there's reason to hope the circuit will work.

#### BobK

Jan 5, 2010
7,682
Supplying AC would reverse the chemical reaction 60 times a second, so no corrosion. But if the circuit only conducts when hit by a bubble and the current is kept low, I think corrosion might not be a problem with DC.

Bob

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