Water leak alarm - Page 1
Forum section: electronics / projects

author: ProDrawerCom
author_rank: Newbie
timestamp: July 31, 2012, 01:20:06 am
content: I know almost nothing about electronics. Tried a year or so ago at age 65 to learn it. My eyesight went bad within a few months and I could no longer read schematics or component numbers, etc. But I’d like to build something to protect my new kitchen hardwood floors. Thought I’d get some kind of a plastic pan to put under dishwasher and refrigerator and sink. The pan would be slightly tilted to let any water drippage roll down to a collector trough which would set off an alarm or just an LED. Can someone tell me where to start? ThanksPS: I know that water leak alarms are commercially available, but none of them are designed just the way I want mine to be.

author: Bored@Work
author_rank: Super Contributor
timestamp: July 31, 2012, 05:07:29 am
content: The classic one is an Aspirin tablet and a specialty prepared clothes peg holding the tablet.The peg is filed a down a bit and is equipped with contacts, the Aspirin gets stuck in the peg between the contacts to keep them open. Aspirin, when getting wet, quickly dissolves, the contacts close, and if you connect a buzzer and a battery to it you have your alarm.

author: vk6zgo
author_rank: Super Contributor
timestamp: July 31, 2012, 06:29:48 am
content: Quote from: Bored@Work on July 31, 2012, 05:07:29 amThat is classic Engineering ,no PICs,no other high tech crap--it just does the job asked of it!Bravo!

author: digsys
author_rank: Unknown
timestamp: July 31, 2012, 09:14:47 am
content: Quote from: vk6zgo on July 31, 2012, 06:29:48 amBut .. how do you reset it? ... and how do you calculate dA/dT? (de Asprin / de Time)

author: Rerouter
author_rank: Super Contributor
timestamp: July 31, 2012, 09:41:27 am
content: reseting it would be to stick in another asprin, or just something between the contacts, from its intended purpose you want the thing to keep warning you till you reset it,also the disolving rate of an asprin isnt that critical, it is merly there to act as a presence of water sensor more than an amount of water sensor,

author: SeanB
author_rank: Super Contributor
timestamp: July 31, 2012, 03:32:42 pm
content: Yes, more a " Hey, the washing machine just did a number recently, better get in here" than"There is 2.736 litres of water occupying 3.56891 square metres of the floor, please attend to this within 3 minutes" thing. The asprin is a good thing, though here it would be eaten by the roaches. I give them regular meals of borax and castor sugar, and nice insect chalk, so every so often you find one doing backstroke. Tough little things, some survive me stepping on them the first time.

author: digsys
author_rank: Unknown
timestamp: August 01, 2012, 12:59:57 am
content: You geeks are funny .. It was supposed to be a jokeQuote from: SeanB on July 31, 2012, 03:32:42 pmMATE !! Just pay the ransom !!

author: ProDrawerCom
author_rank: Newbie
timestamp: August 01, 2012, 01:21:37 am
content: Quote from: Bored@Work on July 31, 2012, 05:07:29 amI like it. A true McGyver device. Thanks

author: Bored@Work
author_rank: Super Contributor
timestamp: August 01, 2012, 05:25:57 am
content: Quote from: digsys on August 01, 2012, 12:59:57 amCut SeanB some slack. He might have posted this from the pub, being busy to celebrate the swimming gold medal, and doing the "feeding the fishes" (and feeding other critters) thing to make room for more beer.BTW, there is a reason I wrote "classic". The Aspirin thing is not my invention. It is, for example, used since ages in some colliders (although not the LHC) to detect water in the tunnel.

author: SeanB
author_rank: Super Contributor
timestamp: August 01, 2012, 03:52:16 pm
content: Sorry, not a drinker, though I am neighbours with le Clos' uncle. He is over the moon with delight.I live in a coastal tropical city, roaches are a part of life, like in NY. They do get big here, and are tough.

author: saturation
author_rank: Super Contributor
timestamp: August 01, 2012, 04:14:47 pm
content: This device is designed to work under those conditions.http://www.amazon.com/Glentronics-BWD-HWA-Basement-Watchdog-Sensor/dp/B000JOK11K/ref=sr_1_3?ie=UTF8&qid=1343837094&sr=8-3&keywords=water+alarmI paid $4 each for mine. Essentially its a CD4000 series oscillator with a buffered switch connected to those contacts; the contacts are on a 3' long wire than can be removed from the unit and positioned anywhere that water collects. If you short the contacts, it lets out a piercing siren, and its powered by a 9V battery.Just remember to replace the battery every 5 years and you're set. I've had mine for almost 15 years, and its saved my floors 2x when a pipe burst and a water heater leaked. To remember to change batteries I put the change schedule on my Casio databank watch, which can keep recurring dates in memory indefinitely. In rings annually, but it reports the install date, and reminds me to also check the operational status. I write the install date with sharpie pen on the battery and change it every 4 years instead of 5 for a safety margin.You can easily build this circuit, but I doubt you can do it for $5-10 each unit.Quote from: ProDrawerCom on July 31, 2012, 01:20:06 am

author: 6502nop
author_rank: Regular Contributor
timestamp: August 03, 2012, 05:58:41 am
content: This basic circuit was originally designed for your purpose, but used as a simple continuity tester. All you need to do is use galvanized probes for the water detection (anything that won't corrode), and make sure you get a -buzzer-, not a piezo element. A buzzer will have it's own built-in driver. If you're in the States, Radio Shack has them for about $5. Add three resistors, a transistor, and a 9V battery/clip on a perf board, and you're done.My water alarm was made on perf, screwed to an old 5.25" plastic panel from a PC case, with two copper stand-offs poking out the bottom for the probes. I just plopped it on the floor with the stand-offs hanging over the edge of the sump, and if the pump failed, the water level would rise, contact the two probes, and sound off. Worked great, but I had lots of probe corrosion problems.nop

author: Unknown
author_rank: Unknown
timestamp: August 04, 2012, 11:42:33 pm
content: Some dishwashers etc are fitted with a shallow tray underneath, and in the tray is a polystyrene float which triggers a microswitch, the switch in turn tells the controller to shut the inlet water off and run the drain pump, the inlet water system is called an Aquastop. I think catching the water is important, as a small drip unnoticed does a great deal of damage before you even know you have a leak.

author: saturation
author_rank: Super Contributor
timestamp: August 05, 2012, 11:50:54 am
content: With this transistor design the input impedance at turn on is at worst ~12k compared to the CMOS design which is in the megaohms, corrosion is faster with higher current. For the 'watchdog' the amount of corrosion on the probe tips has been ~ nil in 15 years.Quote from: 6502nop on August 03, 2012, 05:58:41 am

author: 6502nop
author_rank: Regular Contributor
timestamp: August 06, 2012, 08:02:25 am
content: Actually, the problem with my alarm wasn't corrosion due to excess current draw, but corrosion due to my probes being copper and suspended over a constantly wet sump pit. The petina that developed was so bad, it failed to alert when needed. I plucked it up off the edge, put my wet finger across the two screws on the top (nickel plated, I think), and off it went. I then flipped it over, and there was my problem. The wires, solder, connections, and components were all good - just the copper went bad. Hence, my recommendation for galvanized probes.Remember, I also built this to use as a continuity tester, which I threw into a small cardboard box. That was... gee!... 14 years ago, and it's still working. So, input impedance had nothing to do with it. One had copper terminals, the other just regular alligator clips. It was enviornment and materials, not current draw when activated (practically NO current draw when idle - no on/off switch is needed!).nop

author: saturation
author_rank: Super Contributor
timestamp: August 06, 2012, 06:06:40 pm
content: Yes, thanks for the clarifications. Yes, its a wonderfully simple design, the only current flow at rest would be reverse junction current flowing in the transistor, which is in the nA.Quote from: 6502nop on August 06, 2012, 08:02:25 am

author: SeanB
author_rank: Super Contributor
timestamp: August 06, 2012, 06:16:01 pm
content: Copper probes not the best choice, better is to use 316l stainless steel, so long as the water is not salty. If it is salty then marine bronze would be best, or carbon rods.