water level - how?

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enut
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water level - how?

Post by enut » Mon Feb 24, 2003 2:43 pm

Hi,
I am looking for circuit that would control water level. Once the water would get too low a pump would turn off and stay off for 35 to 45 minutes. I am looking for solid-state circuit that would run off 2 AA batteries if possible. I do not want to turn the pump back on right away and so it would be up to a timer to turn it back on after 35 to 45 minutes.<p>I provide a schematic that might resemble the circuit.<p>Would someone know how such solid-state schematic might look like and what it takes to build?<p>Thank you very much for any feedback.[img]C:/shared/switch_ss.jpg[/img]

bodgy
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Re: water level - how?

Post by bodgy » Mon Feb 24, 2003 3:28 pm

There are a number of ways this could be done, it really depends on reliability.<p>You can just have some conductive strips at the minimum water level and then through a multivibrator of some kind have it switch off when the water level drops thus triggering a pump.<p>You could use a photo sensor or possibly infra-red to basically do the same as above except just a Schmidtt trigger would do instead of an MVB.<p>Or you can actually buy flow switches that are basically a tube with a waterproof micoswitch in them (there are more expensive types used for other purposes). When the water stops flowing the switch changes state.<p>I do have a circuit for the first option I mentioned, it was designed to act as a cheap rain detector to go with the Water Meter in this months N&V, as yet I haven't decided whether to offer it or not. It is nothing outstanding, basically you will see many variations of this circuit on the web if you just do a google search for water or rain detection.<p>Go for the ones that pass an AC wave form through the sensor - the sensor will last much longer!<p>BGMicro actually have some surplus water detector chips from National Semiconducter, these are now obsolete but will do the job all in one. Just add water and probes.<p>Colin
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bodgy
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Re: water level - how?

Post by bodgy » Mon Feb 24, 2003 3:34 pm

Ah make that switch off the pump.<p>For the timer you could try one of the very low power 555s from Zetex. Can't off hand recall the max timeout a 555 would allow. I assume you don't want a series of logic counters as the timing mechanism - you could use a microcontroller which would do the timing and the AC waveform and the sensing. Really depends on your budget and the tools you have to hand.<p>Perhaps downloading the Earth Sciences manual from Parallax might be of use to you.<p>Colin
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enut
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Re: water level - how?

Post by enut » Mon Feb 24, 2003 7:15 pm

I appreciate your feedback guys. As you say, I would like to make it very inexpensive project. I am leaving for a couple of months to Europe and my wife has no idea of how important is to have properly working filter for my fish-tank. If the water gets too low the pump has to shut off. Once the water is at proper level it can start working again. The thing is I do not want to have the pump cycle every minute because the water filled enough for the pump to come on right away, it would not last. That is why I want to turn it back on in 30 to 40 minutes. I thought the micro switch might be good choice but those two conductive strips might be even better as you say. So, now I need figure out how to time it and turn it on/off?!
Thanks.

chessman
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Re: water level - how?

Post by chessman » Mon Feb 24, 2003 9:21 pm

I don't remember the names of some of the chips, but a 32KHz watch crystal through a clock-divider chip will produce a one-second delay, and that could be put through some cascaded counter chips, to give your 40 minute delay. Once that is reached, it could latch the relay for the pump, and then compute another delay, check the contacts again, and if needed, toggle the relay.

chessman
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Re: water level - how?

Post by chessman » Mon Feb 24, 2003 9:25 pm

I'm assuming when you say solid-state you mean without a microcontroller, so you could go about doing it as I said in the above post.<p>If you did have the capabilities of using a microcontroller, it would be much easier to pull off, just a few lines of code. But if you don't already have a programmer and an assembler, along with chips, don't bother.<p>~Kyle

Dimbulb
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Re: water level - how?

Post by Dimbulb » Mon Feb 24, 2003 11:54 pm

Since this is a fish tank the sensor arrangement could use a small float tube attached near the water level it uses a cork that blocks the light path of an led optoisolator located above. This cork is round has a wooden dowel epoxied through it. A plastic container used for perscription pills contains this cork ball. The holes are
top and bottom for dowel and holes in side let water in. The led and detector on top. When in place the dowel is marked with a pencil and sawed to length.<p>If your concern is the circuit going
dead " while left unattended " 2 AA is risky
You could use five 9 volt batteries hooked up in parallel this would be inexpensive insurance compared to not enough power because it had to be special.<p>
A timer monostables through a divide by two. The resistors are 1.5K, 4.7K an adjustable 500K timing capacitor of .22uF. A water low pulse switches on pump and a pulse full switches off the pump and starts the long period timer again.<p>[ February 25, 2003: Message edited by: dim bulb ]</p>

enut
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Re: water level - how?

Post by enut » Tue Feb 25, 2003 3:34 pm

Well, let me see what I can put together. I’ll let you know what I build and how it is working. Thanks for your help. :)

chessman
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Re: water level - how?

Post by chessman » Thu Feb 27, 2003 9:32 am


enut
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Re: water level - how?

Post by enut » Thu Feb 27, 2003 1:33 pm

Yap, that looks really good. All I need is the “S” part that controls the underground tank and it should be working. Then, implementing the counter for the timer should keep it off for certain time. Let’s see if I can make it to work. Thank chessman. :)

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