Wired the circuit, below, on a bread board and all worked fine....the story of my life, then after soldering to a perfboard there was an anomaly!

When the two sensor probes come in contact with water, the alarm and Led supposed to alternate based in the output of pin 3 sinking/sourcing current.
This part functions just as desired, just as it should. HOWEVER! the LED seems to stay on solid when the probes are not in contact with the water and is only intermittent when the probes are in water. Am I actually passing current through the buzzer to make the LED stay on?

Any clues?

 

Hello,

What kind of buzzer are you using?
If the resistance is rather low, the led might stay on.
Also pin 8 in your schematic is not connected (Vcc of the 555)

Bertus

 

Pin 3 of the '555 will always be either high or low. When it is high the buzzer will have voltage and when it is low the LED will have voltage. When there is no water R18 will hold the '555 reset, its output will be low and the LED will be lit. QED

The mystery is how that wasn't the case when it was built on the breadboard.

[EDIT] The above assumes that pin 8 is connected to the supply.

 

Pin 3 of the '555 will always be either high or low. When it is high the buzzer will have voltage and when it is low the LED will have voltage. When there is no water R18 will hold the '555 reset, its output will be low and the LED will be lit. QED

The mystery is how that wasn't the case when it was built on the breadboard.

[EDIT] The above assumes that pin 8 is connected to the supply.

Yes, pin 8 is connected to Vcc...bad schematic! And if this is the case, that the LED is lit, it will be an alternative to a power indicator.
Perhaps it is not such a mystery that it did not appear to happen on the breadboard. The buzzer/Peizo was in the circuit alone while the power was on and I may have added the LED as an afterthought, thus never recreating the real-life scenario. Maybe?

Thanks Bertus & AlbertHall

 

Is the LED intended simply as a 'power is on' indicator, or is it meant to give a visible indication of water detection?
If the former and you're running on battery power you might want to reduce the LED current to prolong battery life.

 

Alec_t,
The LED was originally intended as a second indicator of water which was to alternate at a period of 2 sec with a piezo sounding for the other half cycle. It still functions as intended but remains on if there is no water detected. I was going to add a power indicator LED, but do not have to as the one in use performs both functions. The water detector is part of a control box that branches off to illuminate(via white LEDs) under the sink and adjoining cabinets. The whole system is powered by a single 12V switching power supply. So reducing the current was not necessary although the 1k resistor @ 12v does limit the current to 10mA.