I'm wanting to create a circuit that will connect to the temperature gauge on my boat that will turn on an LED and audible alarm when a selected temperature is exceeded. I' semi -intelligent regarding printed circuit design but need values for components and circuit diagrams. I prefer standard schematics as I call them that i can make a development board with. Any help will be greatly appreciated.

 

There are little thermal switches that will open or close when their temperature exceeds or falls below their set point. Perhaps that is all you need. They cost about a dollar.

But you need to describe in more detail what are trying to do.

 

I installed this on my car dash 8 years ago. Beeps when coolant reaches a selected reading. Add one.



If you reaaaally want to build one; dismantle this to pieces, then you will have all the components needed as a kit and put it back together. Can be removed from your boat dash and leave the probe installed. Your existing dash thermometer can be of a type that cannot be useable tampering with your circuit.

----> https://www.ebay.com/itm/3881081497...xcv5joXfLIBtNJTtE4oI|tkp:Bk9SR5KH4KmhZg&pfm=1

 

So your boat has an existing sensor and gauge but no alarm?

I think the answer in #2 is the way to go. The biggest challenge will be finding a good spot to install the sensor. You’ll then need to get power to your little board with an LED and noisemaker. That might be something you can buy ready made off the shelf.

Do you want to drill a hole and install an LED into your dash? You could replace a board-mounted LED with wires to your custom LED

There are other options. You could build a comparator circuit that would trigger when the voltage across your gauge exceeds a value you can select. For this you would not need another sensor but you’d need to know the voltage that corresponds to over-temperature

 

So your boat has an existing sensor and gauge but no alarm?

I think the answer in #2 is the way to go. The biggest challenge will be finding a good spot to install the sensor. You’ll then need to get power to your little board with an LED and noisemaker. That might be something you can buy ready made off the shelf.

Do you want to drill a hole and install an LED into your dash? You could replace a board-mounted LED with wires to your custom LED

There are other options. You could build a comparator circuit that would trigger when the voltage across your gauge exceeds a value you can select. For this you would not need another sensor but you’d need to know the voltage that corresponds to over-temperature

what I’m hoping to do is take the signal that goes to my existing temperature gauges and use that to feed a circuit so that I can see what that temperature is and have a set point based on that range of that temperature gauge that is on my dash as you mentioned in your second option. Since I have an auto visual alarm oras you mentioned in your second option. Since I have an auto visual indication of temperature. All I need is a audible alarm to tell me that it has gone over temperature since I don’t check my gauges that often while I’m driving the boat. This weekend I will measure my voltage based on different temperature readings on the temperature gauge to give me an idea of what range I need to be in.
i’m 83 years old and trying to learn more about circuitry and have made some other projects that I’ve used on my boat that it worked well it’s just I have not really versed in the specifications of the components for a circuit of that type. So any help would be greatly appreciated

 

I think you can probably use something like these:
https://www.amazon.com/Comparator-Overvoltage-Undervoltage-Protection-Comparison/dp/B09TR87JTX
https://www.amazon.com/ELECTRONICS-SALON-Voltage-Comparator-Module-Relay/dp/B014H0U5IA
or maybe
https://www.amazon.com/Comimark-Board-Battery-Voltage-Protection/dp/B07XM7YL4N

I don't have experience with and don't endorse any of these, I just grabbed them fast to illustrate that you shouldn't have to reinvent a wheel here. You can get something ready-made to get you most of the way.

All these rely on the concept of a voltage comparator such as the LM393 integrated circuit chip. When a test voltage exceeds (or falls below) a reference voltage, the chip changes the state of its output and that signal can then trip a relay or otherwise control the power to a light, noisemaker, whatever.

 

Can you give us any information about the temperature gauge or sensor or engine etc. Maybe Stewart Warner, or something written on the dial?
It makes it easier to come up with a circuit or maybe an off the shelf module could be made to work.

The coolant temp sensor is likely a thermistor- which means its resistance goes down as temperature goes up.
It's a 12V boat?

 

I think you can probably use something like these:
https://www.amazon.com/Comparator-Overvoltage-Undervoltage-Protection-Comparison/dp/B09TR87JTX
https://www.amazon.com/ELECTRONICS-SALON-Voltage-Comparator-Module-Relay/dp/B014H0U5IA
or maybe
https://www.amazon.com/Comimark-Board-Battery-Voltage-Protection/dp/B07XM7YL4N

I don't have experience with and don't endorse any of these, I just grabbed them fast to illustrate that you shouldn't have to reinvent a wheel here. You can get something ready-made to get you most of the way.

All these rely on the concept of a voltage comparator such as the LM393 integrated circuit chip. When a test voltage exceeds (or falls below) a reference voltage, the chip changes the state of its output and that signal can then trip a relay or otherwise control the power to a light, noisemaker, whatever.

Thanks, the first option is almost perfect. I ordered one and will test it when it arrives.