Looking for water sensor to controll relay.

[SA057]

I am using the cheap $10 sensors with a buzzer around the back of my tank to detect water leaks. I have added some automation to my system with high/low water float switches and a power off alarm that calls my cellphone. I want a water sensor that will trip a relay and can be used with the floatswitches too. Any DIY stuff or cheap sources?

[BrainBandAid]

You could try and hack your cheap alarm and put a small relay on it instead of the buzzer... that might have to run a bigger relay, but it would work. You'd have to find the voltage the buzzer runs on to get the right relay.

[SA057]

I did try that. There are only a few parts in it and I could not get a voltage reading off the buzzer. It works off a 555 timer relay but I don't know how to hack it.
I found a diagram of a DIY that looks just like the store product that I have, but I still don't see how to add a relay to it.

http://reefcentral.com/gallery/data/500/115850alarm.gif

[BrainBandAid]

According to the ic datasheet, with 15v in, you can source up to 200mA out, at 12.5v. That's enough to drive pretty much any 12vdc relay.
You could probably simply take the buzzer out, and connect the relay coil leads in place of the buzzer.
If you needed to, use a DPDT relay and use one set of contacts to latch the coil in. (Might have to use a reset button, too). Not quite sure what the 1uF cap is there for...

Hope that helps!

[SA057]

Thanks, I will try that and replace the buzzer with a relay. I just couldn't get any voltage reading with the buzzer there. :rolleyes:

[BeanAnimal]

The 555 timer is working as an oscillator (an astable multivibrator). It is not going to drive a relay in that configuration. The speaker is being driven in current mode. In other words the 555 timer is creating a signal that goes from positive to negative at 1kHz or so (adjustable by the resistor values)

[SA057]

That is about what I thought. Is there a way to DIY something else that will trip a relay?

[BeanAnimal]

You can use capacitive sensors to trip a relay. There are dozens of eamples online (discovercircuits, etc). Also consider posting to rec.electronics.design or another good usenet group.

[BeanAnimal]

http://www.google.com/custom?domains=www.discovercircuits.com&q=water+sensor&sitesearch=www.discovercircuits.com&client=pub-9840570490567972&forid=1&channel=4570182912&ie=ISO-8859-1&oe=ISO-8859-1&cof=GALT%3A%239A2C06%3BGL%3A1%3BDIV%3A%2333FFFF%3BVLC%3AD03500%3BAH%3Acenter%3BBGC%3A99CCFF%3BLBGC%3 ACCE5F9%3BALC%3A440066%3BLC%3A440066%3BT%3A336699%3BGFNT%3A223472%3BGIMP%3A223472%3BLH%3A0%3BLW%3A0% 3BL%3Ahttp%3A%2F%2Fwww.discovercircuits.com%2F_borders%2Fdc-new-logo2.jpg%3BS%3Ahttp%3A%2F%2F%3BLP%3A1%3BFORID%3A1%3B&hl=en

[BeanAnimal]

http://www.zen22142.zen.co.uk/Circuits/Switching/waterrelay.htm
http://www.uoguelph.ca/~antoon/circ/sensor1.htm
http://www.discovercircuits.com/DJ-Circuits/h2oalm.htm
http://www.uoguelph.ca/~antoon/circ/sensor3.htm
http://www.national.com/an/AB/AB-10.pdf (not sure if the LM 1830 is still available... it was big in the auto industry for windshield wiper tanks.)
http://www.aaroncake.net/circuits/raindet.htm
http://www.electronics-lab.com/projects/science/015/index.html (same as above i think, added in case one has errors)
http://www.wenzel.com/pdffiles/rainsens.pdf
http://www.zen22142.zen.co.uk/Circuits/Alarm/water_lev_alm.htm

[BeanAnimal]

All of the circuits above can be adapted to your use. Some are one shots and reset when the water disapears, others must be reset. For the one-shots you would simple use them to trip a latching relay if you wanted a persistant alarm condition.

[SA057]

Great thanks, I am looking through them now.

[stugray]

You could also change the values of the resistor(s) to give a long pulse ( 5-10 ) seconds instead of the 1 kHz signal. The pulse would close the relay and then have the relay self latching. This would require a reset button to open it when you want. How to do this with the 555 timer is available online or from the project book that you can buy at radio shack.

Stu

[BeanAnimal]

You would need a transistor to drive the relay in that case, but it would work.