please help a supern00b building a 12V timer

[studioso]

hello,
I have a young 3 year old son with mild autism who loves to play with water for hours at end. I'm planning to build a nice water table that will keep him occupied this summer.

I pretend to be very handy with tools, but honestly I can use some help from "the internets" with the electronics here:

I want the water to be flowing constantly (as he mostly likes to catch it in a cup) so I'm planning to place a small pump under the table that will pump the water back to a spout on top.
since the table is outdoors, and I don't want to mix water with high voltage, I was planning to use a 500mA 12V battery pump such as this one:
http://www.amazon.com/submersible-W...WIR0/ref=sr_1_3?ie=UTF8&qid=1334608903&sr=8-3

I will place the pump and battery in a sealed box under the table, but I'm assuming that even in the worst case scenario that the battery will somehow short to the water table 12V will not give my kid a shock. is that correct?

2- ideally, I want to set the pump in such a way that by pressing a button, it will turn on, and after a set time (say 5 minutes) it will go off, until someone pressed the button again. (otherwise the thing will be left to run overnight...)

is there a timer that I can buy and place in line between the battery and pump?
How can I go about building one?
cash is short, so I'd like to keep this on the cheap.

I have experience with a soldering iron, and I've build some circuits before, but I'm afraid I forgot most of what I knew. but I'm a fast learner!

I understand that perhaps I might be asking for a lot. I'm relying on the kindness of strangers to help me for nothing in return but gratitude!

thanks for reading,
Alex

 

[CocaCola]

You might want to really consider a larger boat bilge pump, or a larger fountain pump... The thing you will find very quickly is that these little pumps have horrible maximum head aka how much vertical lift of the water they can accomplish... If you put it under the table, you already need a foot or two of lift just to get to water level, maybe another 2 feet of lift to actually be usable... The higher you go with any pump the less volume of water you get so that is important as well, if you want say one gallon a minute flow rate make sure at the worst case height you have at least that volume of transfer... You need to really watch the volume at the working height you need, no the advertised maximums or recommended working height...

The one you have linked is documented kinda funny on Amazon, if it truly has a 3.8L/m rate at 2.5M lift you would likely be AOK

The risk of shock is very minimal with your idea @ 12 volts...

As far as building a circuit, for the cheap and dirty you might want to look at those bathroom heat lamp timers at the hardware store, the old dial ones NOT the push button ones... If my memory serves me correct they are mechanical dial timers and thus should work at 12 volts even though they are designed for 110v applications... Not the ideal '5 minute' push button but just the same it can't be left on overnight...

Example

http://www.amazon.com/Westek-TMSW30MW-Hardwire-Mechanical-Countdown/dp/B002YGS6JU

 

[studioso]

thank you for your answer, coca cola.
about the pump head: I figured that if the pump is stuck under the table, all I need is a lift of not more than 2 feet, and I really need very little flow: I'm OK if say it fills a 8 Oz cup in 7-10 seconds,
about the timer idea: ideally I'd like the kid to press the button when he wants to play, and press it again every 5-10 minutes to keep the pump going (I'm also assuming these pumps will not survive running for long periods of time) but I guess the timers would be an alternative. I didn't know that these work even on lower voltages: I have a few of them, the kind that go between a plug and a socket.
thanks again

 

[CocaCola]

OK my question is, if I was to build you the bare minimum resettable 5 minute countdown circuit, are you capable and willing to build and provide the button/housing/wiring/hook up the relay and what not?

 

[studioso]

Most certainly!
-all I need to know is were to connect the button, the battery, and the power out. am I right?
I live in Montreal and we have a few big electronics stores that will have anything I'd need.

also, I have no clue what you would build, but can you place a pot so that the actual time can be adjusted? I don't think that that is critical, but if it's easy, it might come in useful.

would you kindly give me a price?

thank you very much!

 

[CocaCola]

A pot to adjust the delay is no problem, let me think this over for a bit and I'll get back to you...

And yes all you would need to do is source the remaining parts and wire it up...

Although you likely won't find it local, may I suggest you getting the button online, I envision a very sleek finished device using an arcade push button, all mounted in a nice project box... You can get these buttons on Ebay for about $2 delivered... They even have some huge 60mm buttons for about $5...

 

[studioso]

just what I was thinking! I can get the standard arcade buttons here for 4-5$, but 60mm button sounds even better.
I'll await for your reply.
thanks again.

 

[studioso]

any news?

 

[gto_ron]

I'm sure CocaCola will give you an excellent circuit. If you're still looking, an SN74123 dual, retriggerable one-shot will provide all the timing you need and it's user friendly as well. 12V is fine for powering it but it won't drive the pump alone. It can drive a relay with the pump 12V line going through.

12V won't hurt anyone unless you put your tongue between the terminals, not that I've ever done that with 9V batteries.

regards

ron

 

[timothy48342]

...
12V won't hurt anyone unless you put your tongue between the terminals, not that I've ever done that with 9V batteries.
...

If anyone out ther has not yet put a 9V battery on their toung they should do it just twice. The first time to learn what that is like. The seond time is differnet, becauase you know and your doing it anyway.

I just want to point out a physics thing. If you have a deep tank and you want to a pump to lift water all the way from the bottom of the tank to a position... say... 6 inches above the water-line, the pump only has to have enough pressure to lift the water 6 inches. You don't have to take into account the depth of the tank. The input at the pump is under pressure, too, so it offsets the additional distance the water must be lifted.

I hope that CocaCola can make a circuit for you studioso. I also hope that you 2 keep the conversation public. (It's about someone into electronics making money off a hobby... that sort of thing. I like it.)
--tim

 

[CocaCola]

I hope that CocaCola can make a circuit for you studioso

I'll be in contact with him shortly, I have a lot on my plate right now so this gets pushed aside...

 

[studioso]

thanks Cocacola, just keep in mind that summer up here in Montreal lasts about a week and a half... we don't want to miss it!

 

[CocaCola]

I'll try and get to it this week, just have a project that needs to be wrapped up that is on the bench right now...

 

[CDRIVE]

thanks Cocacola, just keep in mind that summer up here in Montreal lasts about a week and a half... we don't want to miss it!

Well, where I'm located summer never ends. It's just a matter of blistering hot or Chamber Of Commerce weather. So I here you go.

I used a power FET to drive the motor but it can be replaced with an appropriate relay or an NPN Transistor. The current draw of the pump motor shown in the plot is just off the top of my head. It may be a bit higher or lower depending on the 12V pump that you buy. IMHO a bilge pump, even the smallest available, is a bit of overkill. I think something on the order of an aquarium pump would be a better choice for this application. Feel free to ask any questions.

 

[studioso]

cdrive, you are the man.

I have no idea what I put together, I think it runs on black magic, but it works! runs just under 8 minutes!

thank you so much! electronics cost me about 6$. except for the battery, of course, which I had,, nd the pump which I got on amazon:

DC 12V 6.5L (100GPH) CPU Cooling HHO submersible Water/oil Pump

cdrive, I can't thank you enough. it's for guys like you that the internet was created!

now, if I may ask (out of curiosity) what actually dictates the time that it will run? is it all 4 capacitors? so what if -for example- I wanted it to run for shorter or longer, what would I adjust?

 

[jackorocko]

http://www.kpsec.freeuk.com/555timer.htm#monostable

this is how it works. it also gives you the formula for the time period. C1 and R2 set the time period

 

[CocaCola]

Replace R2 with a pot and you can dial it in to different times easily, or at least have flexibility...

In addition to the calculator...

Since I see a multi meter in your picture you can measure the pot at different settings so you can re-calibrate easily or replace with normal resistor...

Glad it's up and working for you, I was going to get to it this weekend but it's always good to see someone do it themselves...

 

[CDRIVE]

Wow, you are a quick study! I really didn't think I'd check in here today to see that you breadboarded it overnight. Before I became old and decrepit I had that kind of **** and vinegar.

Anyway, as jackorocko said R2 & C1 (RxC) determines the time period. If you want to vary the timeout at will you can replace R2 with a Pot, as CocaCola suggested. One caveat though! Make sure there's a fixed resistor (1K will do) in series with the Pot. This is because a Pot set to zero Ohms is not healthy for the Discharge pin. It will also short the supply voltage (Vcc) to GND when the Discharge pin goes low.