Warning light System for a Boat

Im working on a EMD Project for class and my idea was to create a warning light system for my airboat. Im running a small block chevy motor with Faria gauges and sending units like the one below

http://www.classicairboats.com/Sending-Unit-Temperature-Faria-20825.Item.html

My idea is when the motor gets up to a temperature of 220 it will trigger a yellow led then when it gets to 230 have a red led come on and if it gets to 240 have it flash the red led. Then maybe do the same type of thing for oil pressure and voltage. So this way I don't have to stare at my gauges while driving the boat.

How would I go about wiring something like this and what all would I need to make it work? This is my first time using an ardino but have programmed with matlab in the past. Im not sure where to find more information on the seding units and how to make them compatible with my arduino uno? Any help would be much appreciated. Thanks

The most important thing to note that when using 12v systems, you need to make sure the highest voltage on any input is 5v.

What type of temperature sensor are you using?

The basic code is to read the temperature then use it to select the colour LED by looking at a range of value bands.

If temp between 220 and 230 turn on yellow If temp between 230 and 240 turn on red If > 240 flash red

Weedpharma

Mr. Google says that these “Faria” sending units (temp, pressure, fuel … everything) give a varying resistance in the range ~25ohms to ~200 or ~25 to ~1K ohm.

dhpt99:
How would I go about wiring something like this and what all would I need to make it work? This is my first time using an ardino but have programmed with matlab in the past. Im not sure where to find more information on the seding units and how to make them compatible with my arduino uno? Any help would be much appreciated.

First thing would be: Identify your sensor and find the datasheet showing the technical specifications.

Is it this: http://faria-instruments.com/site_manuals/IS0085E.pdf

And your sensor is the “Water temperature - American Marine Sender” with the data:
100°F - 450 Ohms
175°F - 99 Ohms
250°F - 29.6 Ohms

If so, the easiest way of sensor operation would be at Arduino 5V Voltage and a series circuit of the sensor and a resistor.

Schematics like:

       Resistor        Sensor 
       _______         _______
5V ---|_______|---+---|_______|--- GND
                  |
                  |
                  |
                Arduino
              analog input

For best results chose the resistor value like that:
What temperature is of most interest for you to get accurate measurement?
If this is the range 175°F - 99 Ohms to 250°F - 29.6 Ohms chose the resistor in the same range.
So perhaps chose the resistor to be R= 68 Ohms

The rest is math and programming.

What exactly do i need the resistor for? I read the aurdrino goes off voltage readings so would i look for the voltage drop for my program? And doesnt the gauge run off 5 volts already? Sorry im really new to this but really appreciate all the help!

dhpt99: What exactly do i need the resistor for? I read the aurdrino goes off voltage readings so would i look for the voltage drop for my program?

If you build the circuit like shown above, the resistor and the sensor provide a "voltage divider".

This means: The voltage from one end to the other is constant (5V), but the "voltage in the middle" depends on the resistance of resistor and sensor.

If the resistance of the sensor is the same as the resistor, you can measure 2.5V in the middle. If the resistance of the sensor is higher than the resistor, you measure more than 2.5V. If the resistance of the sensor is lower than the resistor, you measure less than 2.5V.

From the voltage you measure in the middle of the voltage divider, you can calculate the actual resistance of the sensor by using Ohm's law for calculation.

And from the resistance of the sensor you can then calculate the current temperature.

As a first step, you perhaps build the circuit and just measure the ADC value by using the analogRead() function. If everything is fine with the circuit, you should see: higher temperature ==> analogRead() value becomes lower lower temperature ==> analogRead() value becomes higher

ok that makes sense. Can I get the 5V to go to the resistor from the 5V output on the board? And this wont affect the readout on the existing gauge that I have hooked up to the sending unit will it?

dhpt99: Can I get the 5V to go to the resistor from the 5V output on the board?

Yes. Normally you can easily take up to 400 mA from the 5V output of the board (depends on how you provide board voltage), but the voltage divider will hardly use more than 50mA. So that would be no problem.

dhpt99: And this wont affect the readout on the existing gauge that I have hooked up to the sending unit will it?

You cannot have easily such thing as an 'existing gauge' as an additional device connected to the sensor.

You can have either the Arduino with your sensor. Or you can have another "existing gauge" with your sensor. But not both at the same time.

Most likely your "existing gauge" even is not operated by 5V voltage, so Arduino voltage and "existing gauge" voltage are not compatible.

If you want to get a signal from an "existing gauge" to work at the same time with the Arduino, you most likely will have to open and reverse-engineer your "existing gauge" and find a signal that you might use for the Arduino. I cannot give you any advice on that, because I don't know anything about your "existing gauge" and its inner working.

Connecting Arduino microcontrollers to devices powered by an existing on-board power supply of motor vehicles is not a thing for arduino newbies. Doing so would require high efforts to provide electromagnetic immunity against disturbances caused by the very dirty on-board power supply of motor vehicles.

The only easy thing would be: Use the sensor exclusive with an Arduino.

While you're at it , couple your oil pressure and coolant faults into a common alarm and drive a pulsing car horn. Coloured LEDs can be missed just as easily as gauges.

Hello everyone,

I red your conversation with huuuge interest! This kind of systems are guarantee of security, besides maritime sollutions are meaningful too - VSAT sollutions or mobile handhelds. I work at board on Denmark, we're using Iridium Pilot and Thuraya XT. Great stuff, I know that our distributor is IEC Telecom Group. Maybe you heard about it, check on their webside: http://www.iec-telecom.com , if you want.