Hi, guys. I built a circuit to water my propagator every 6 hours for 5 seconds. The circuits works great but I am getting concerned that it may malfunction at some point. I have myself a water sensor, and was wondering if it would be possible to build a circuit that could kill power to the circuit in the event that the sensor gets covered in water?

I have done some searching and built a couple tests but none of them actually work

I am just after a circuit that will send power to "output" until the sensor senses water then power is killed.

Thanks.

Dan

 

Can't really help without knowing the output of the water sensor.

 

http://www.reuk.co.uk/wordpress/reuk-shop-water-conservation/buy-liquid-sensor/

It's that one mate

 

Hello,

What are the specifications of your waterpump?

On the give page the specs of the sensor tell me that it may be used for max 100 Volts DC and switch 10 Watts:

Technical Specifications
This liquid sensor can handle a switching current of up to 0.5 Amps, the maximum switching voltage is 100 VDC, and the maximum switching capacity is 10 Watts. Where the circuit or appliance to be switched on exceeds any of these limits, a suitable relay or transistor should be used.

Bertus

 

the pump is on a 12vdc circuit and runs off a relay. Can't remember the exact spec of the pump, but it is powered by a 12v 5 amp relay without an issue

 

in fact http://www.zen22142.zen.co.uk/ronj/rt8.html is the exact build

 

Hello,

Then the sensor will need some extra help to switch the power off, as it can handle 0.5 Amps max.
One of the ways is already given in the spec, using a relays.
You might put the sensor in series with the coil of the relays you are already using.

Bertus

 

My original idea was to use a transistor to to kill the power. Energise the base from water sensor to kill it.

Would this not work?

 

Hello,

Could you post a schematic of the intended modification?
You can upload files using the "Upload a File" button.

Bertus

 

I was thinking something like this, where I use a PNP transistor instead of the NPN and LED is the circuit output.

What do you think?

 

I don't think you can rely on the information given for the sensor. As is says it contains a reed switch (Which probably means a reed relay) there must be a minimum voltage required to drive the coil which it does not specify. It also says "can be used in any non-corrosive liquids with the exception of thick oils" As the picture points out the gold contacts it suggests that it works by the liquid providing a conductive path between these contacts. It does not say that the liquid needs to be conductive.

Les.

 

Ok, I built a test circuit based on the one above, I replaced the transistor with a PNP and it work pretty much the way I would expect. I just need a little more resistance at the base. For whatever reason the switch (water sensor) is giving off almost the same voltage going in when it is sitting out of water, this means it is always powering the base enough to kill the circuit.... I put my finger between a resistor and wire (creating more resistace) and the light came on and went off as I would have liked. But will this be good enough for my circuit?

 

Just another idea.

I have not actually verified that this will do what you want but the idea is to detect conduction between an isolated 12v power supply and 'Earth Ground".

If the "-" side of the power supply comes in contact with "Earth Ground" (A metal rod in the ground) , the attached circuit should detect it.

Use the outputs of the CD4011 (or any other CMOS logic chip similar) to drive your transistor relay driver.

 

Interesting that on the web page, if you reverse the polarity of the connection, it's on when dry. Doesn't say if it's off when wet.

Ken

 

Hello,

@KMoffett , here is the note of reverse connection:
* Note that if the sensor is wired the other way around (reverse polarity), the internal switch will be ON whether the sensor is wet or not.

As I read it, it is ALWAYS ON when reversed.

Bertus

 

You are right mate. And I stupidly wired mine.up.backwards while doing circuit tests lol. Got.it working now.though just a little curiouser as to why I have current on both.sides of a dry switch though... Not that it.is.important. It is working. I am just waiting to finish work so I can test it a few times

 

You are right mate. And I stupidly wired mine.up.backwards while doing circuit tests lol. Got.it working now.though just a little curiouser as to why I have current on both.sides of a dry switch though... Not that it.is.important. It is working. I am just waiting to finish work so I can test it a few times

Why not wire your sensor across the reset switch?

 

Did not think that would work?

 

Ok, I am just waiting for my last resistor to arrive, ran out and didnt know. when this gets here, I am going to try using the reset circuit for the cut off safety Thanks for that idea. If all works well then photos are to follow.

Cheers

Dan