Battery powered 3v water sensor

Apologies if this is in the wrong forum. I am relatively new to circuitry design having only built my own homebrew relay board.

I am trying to build a very simple water detection circuit that I will use to trigger an X10 DS10a module. The DS10a is basically just a simple alarm module used in X10 systems that has a NC circuit that is manipulated by a magnetic reed switch. When the circuit is opened the unit sends an RF pulse and when the circuit returns to NC it sends another RF pules indicating that it has changed state. If I am correct the magnetic reed switch either breaks a ground or completes a ground circuit. That's the background of the DS10a. It's really meant to be used as a wireless window or door alarm in an X10 security system.

I intend to replace the magnetic reed switch with a piece of circuitry that is able to detect water. I plan on building 7 or 8 of them and putting them around the house to detect a water leak and hopefully alert me before my house is destroyed.

The module is powered by 2 AA batteries so I am looking to build something that will work with 3VDC. Since they will be battery powered I need it the circuit to be as low powered as possible and I was planning on using some cheap MOSFET transistors. The circuit can either close the ground circuit or open it. In simple terms I just need to switch a ground when water is detected.

So far I've designed a simple leaf board that uses a series of close traces, that when water contacts them should complete a high resistance circuit. I plan on wrapping the leaf board in a sponge with same salt so the resistance should be less than 10k Ω or so once the water hits it I think.

The part I am struggling with is how the circuit would be built around the MOSFET transistor. I found this webpage which seems to explain how to build one using a MOSFET transistor to switch the ground on an LED.
https://www.electronics-tutorials.ws/transistor/tran_7.html

Before I try to manipulate this design to do what I want it to I just wonder if I am going in the wrong direction or if there is a better way to do this.

Thanks

ReddHead said:

So far I've designed a simple leaf board that uses a series of close traces, that when water contacts them should complete a high resistance circuit. I plan on wrapping the leaf board in a sponge with same salt so the resistance should be less than 10k Ω or so once the water hits it I think.

Click to expand...

1. Remember each time after a water hit, when the water level will be lower than the sensor, you have to unwrap your sensor, remove salt etc., dry it, and set it again.

2. How long the alarm will stay on ? As long as the water level high?

papunblg said:

1. Remember each time after a water hit, when the water level will be lower than the sensor, you have to unwrap your sensor, remove salt etc., dry it, and set it again.

2. How long the alarm will stay on ? As long as the water level high?

Click to expand...

Drying it out after it makes contact with water is not a big deal. Much better than having a water leak.

It only needs to be a momentary switch, just long enough so that the sensor. Circuit. In the ds10a is broken.

The MOSFET for sure could be used to detect the water level.
Here is one other solution - a simple capacitive sensor suitable for water level detection. It could be also used for proximity and touch detection. It uses 556 timer and is tested and works reliably well. Enjoy it.

ReddHead said:

Drying it out after it makes contact with water is not a big deal. Much better than having a water leak.

It only needs to be a momentary switch, just long enough so that the sensor. Circuit. In the ds10a is broken.

Click to expand...

Then you can go for a mosfet switch. But the circuit in the above link needs slight modification.

And If you use a MOSFET based monostable as a switch, you can control the "switch on" time period.

---------- Post added at 19:29 ---------- Previous post was at 19:24 ----------


As it is designed for logic level inputs we know that when the gate is connected to ground it is turned off and when the gate is connected to 5 volts it is turned on. We do not need to use a resistor between the push button switch and the gate because the current is very very low whatever the input voltage (if kept within 0 to 5 volts).

see https://brunningsoftware.co.uk/FET.htm

---------- Post added at 19:30 ---------- Previous post was at 19:29 ----------

Adjust R2 according to your need

papunblg said:

Then you can go for a mosfet switch. But the circuit in the above link needs slight modification.

And If you use a MOSFET based monostable as a switch, you can control the "switch on" time period.

---------- Post added at 19:29 ---------- Previous post was at 19:24 ----------

As it is designed for logic level inputs we know that when the gate is connected to ground it is turned off and when the gate is connected to 5 volts it is turned on. We do not need to use a resistor between the push button switch and the gate because the current is very very low whatever the input voltage (if kept within 0 to 5 volts).

see https://brunningsoftware.co.uk/FET.htm

---------- Post added at 19:30 ---------- Previous post was at 19:29 ----------

Adjust R2 according to your need

Click to expand...

Thanks. This is a pretty simple circuit to build.

I would like to mention one thing. This kind of switch to trigger an alarm or other circuit , can also be created using CMOS gate IC(4000 series) based monostable circuits. 3V to 15V voltage. Suitable for battery powered operation. And very very low current consumption during stand by time.

I like to mention more, you can use an UM66 Ic for the alarm sound.