I use a watering system with a 3 gallon jug attached. It's convienent, except I don't always notice the pooch is out of water in a timely manner. So I sketched this up for a weekend project.



Just thought I'd put this out there.

 

What does the croc clips sense ?

 

Don't see why you need Q2, just put the collector of Q1 to the 555,

Or use a pull up resistor on pin 4, and use the crocodile clips on pin 4 and pin 1, then when the water is low it buzzes, you may need to put the buzzer and led to pins 1,3.

 

Two words:

Battery life

By using a really high gain transistor I can raise the resistance of all the parts, Never having experimented with pin 4 upper limits on resistance I chose what works. Speaking of which, guess I need to up R3 to 1MΩ.

The alarm sounds 1/2 seconds out of 5 minutes, enough to be noticed.

The alligator clips are the sense input.

 

With such a small current through the clips, hopefully electrolytic corrosion won't be too bad. If it proves bothersome you might want to consider energising them with AC rather than DC.

 

We shall see.

Thanks.

 

What is the sensor ?

 

the Reset minimum voltage level is 1V, so anything above 1 V and the chip will run ok, below 1V it resets.

 

What is the sensor ?

It senses whether water is between them, conducting. DI water is an insulator, but water in the wild usually conducts quite well.

the Reset minimum voltage level is 1V, so anything above 1 V and the chip will run ok, below 1V it resets.

On a conventional 555 it is .7 volts, but that doesn't tell me the input resistance of pin 4 on a CMOS 555, or what the maximum reliable resistance to use for the pull up. I agree I could have done it this way (with other changes), but this is the way I choose to do it. My confidence is high this will work the first time, and will only need new batteries every 6months to a year.

 

I would turn on and off your circuit using MOS-FET. Use a very high value resistor to hold the FET off. Put the electrodes from battery + to the FET gate.

Doing it this way, the circuit draws absolutely no power when the electrodes are dry.

 

I would turn on and off your circuit using MOS-FET. Use a very high value resistor to hold the FET off. Put the electrodes from battery + to the FET gate.

Doing it this way, the circuit draws absolutely no power when the electrodes are dry.

Isn't that backwards? When the electrodes are dry, you need it to sound the alert. It can't be zero power consumption when the electrodes are dry.

 

Agreed, which is why it is designed the way it is. This is not a water alarm, but a lack of water alarm.

I'm going to do something different and build this dead bug style on the back of the sonalert.

 

Please post a picture when ready.

 

If you considering the electrolytic corrosion of alligator clips then maybe you could find some steel chopsticks or something similar.

 

Very large paper clips

 

For electrodes that are going to be submerged and conducting most of the time, use AC drive and demodulation, and stainless steel electrodes. TIG welding rods, or SS wire from the hardware store. Keep the clips out of the water. This can be done with CD4093 gates. Maybe with a 556.

Ken

 

Naw, its complex enough, and paperclips are cheap.

Less than 3 microamps isn't much current.