Hi All,
As a Newbie here, I'll apologise in advance for whatever mistakes I'll undoubtedly make.

Here is what I have:

12v DC submerged Bilge Pump (to get the water out of a boat)
Solid State Water level sensor mounted down in bilge (sump at the lowest part of a boat).
Remote On / Off / Auto switch and circuit breaker. 'On' provides direct powering of pump, while Auto routes power through sensor switch to turn pump on when the water rises to a preset point.
The sensor switch has both On and Off triggering points.

What I would like:

A simple circuit that I can splice into the 'auto' part of the circuit that will drive a piezo alarm when the pump starts.
I'd also like to incorporate a 'mute' button for the piezo that could mute the piezo until the sensor switch stops the motor.

Why I'm asking the question here:

Perhaps because of my rather alarming lack of electronics knowledge.

I'm sure there are simple circuits already published, but I can't be certain that they will work as I need them.
So, dunce hat firmly riveted in place, I humbly ask for help.

 

Here's the problem: You already know you can run two wires from the pump to a piezo and put a switch in the line, therefore it begs the question: Are you trying to avoid running the wires?

If true, the pump current must be detected and you gave no specs about how much current to detect.

 

Hi #12.
Thanks for your reply and Yes, I could run wires if absolutely necessary, however in this particular installation, it would be far from a straightforward proposition. The bilge is about 10m from the control panel and running a new pair would involve much pretzel like work from my (slightly) old body.

Hence the desire to come up with some easy to install "Electrickery" to sense when the motor is running (15a)

 

You might be able to use wireless - lots of possible solutions - but you're going to want marine gear and I have no knowledge of that.

 

There are chips to measure current like this one:
http://www.allegromicro.com/Product...p-Integrated-Conductor-Sensor-ICs/ACS712.aspx
The one in that photo isn't big enough for 15 amps, but there are some really beefy sensors. I just don't remember where I left them.
So you run the current carrying wire through the sensor, amplify the results, and send that to the piezo.

Are you up for making a circuit board?

 

There are chips to measure current like this one:
http://www.allegromicro.com/Product...p-Integrated-Conductor-Sensor-ICs/ACS712.aspx
The one in that photo isn't big enough for 15 amps, but there are some really beefy sensors. I just don't remember where I left them.
So you run the current carrying wire through the sensor, amplify the results, and send that to the piezo.

Are you up for making a circuit board?

I have made up boards in the past (dark days of wax and acid) so I'm sure I can come up with something using modern techniques (love my CAD programs).
Whatever the result, I'm hoping for something very compact, so that I can resin encapsulate it.

 

I see here 3 pre-fab circuit boards for <$10. Can't seem to pull any answers out of Adafruit. That might require a phone call.
Bottom line: You might get out of this for less than twenty bucks, but it's going to cost you some time to be sure you're buying what you need. The other option is to design this from scratch, and I can't see why I would do that for less than $20.
http://www.mouser.com/search/Refine.aspx?N=21868864&Ns=Pricing|0

 

I see here 3 pre-fab circuit boards for <$10. Can't seem to pull any answers out of Adafruit. That might require a phone call.
Bottom line: You might get out of this for less than twenty bucks, but it's going to cost you some time to be sure you're buying what you need. The other option is to design this from scratch, and I can't see why I would do that for less than $20.
http://www.mouser.com/search/Refine.aspx?N=21868864&Ns=Pricing|0

Thanks #12. For that kind of pricing, I tend to agree with you. I'll dive in head first and see if I can make sense of what I'm seeing.
Hopefully I'll find a solution before I hit the bottom, but I'm possibly still out of my depth.

Stay tuned

 

If you have a manual bilge pump switch at the helm, that wire gets energized when pump is on from the float switch. You could wire your piezo to that wire & ground.

 

Hi DNA,

About the only thing I can think of to reply with is.................DOH............... and thanks heaps!!!
Yet another case of the retrospectoscope being perfectly in focus. Your drawing points out the obvious and most elegant solution, so thank you, from the bottom of my bilge

 

Working from DNA Robotics suggestion here is a little circuit which can be easily modified to fit you needs:


The Low 3 alarm contact is eliminated and using the line which goes high when the pump is running is power for the circuit. Any 12 volt alarm buzzer can be used. Pressing the Alarm Silence button will silence the audible alarm leaving the Alarm Lamp illuminated. A simple 12 Volt automotive relay will work fine as the latching relay as long as it is a SPDT (Single Pole Double Throw version. When the alarm line goes low (Off) the relay will reset. The idea being you eliminate the audible but still have the illumination lamp function.

Ron

 

Thanks for that Ron and to everyone who has contributed.

It's nice to know that there are still a few places on the net where you can ask an honest question about something you know little about and get answers and lots of help, rather than inane commentary from trolls.

The combination of all the replies has led to an eminently suitable solution and once again, thank you all.