Since getting my Malibu almost 2 years ago, one thing that has bothered me is that we have such high tech boats that monitor our hard ballast tanks, but no way to monitor the bags. Malibu has since added L-shaped rear hard tanks that will monitor the rear bags, but for people with older boats there is not a good solution that I am aware of. Although I am no where near a level of riding that requires super precise filling of ballast bags, I still found myself lifting the rear cushions to look at the bags when dumping bags from full back to 1/2 or empty. So I decided this winter to head down the path of getting me a rear bag monitoring setup going.
I started the research phase looking for a good water pressure sensor that I could use to just drop into the top of the bag. I ended up with a Maretron Submersible Pressure Transducer. The unit is kinda pricey, but has a very low psi range so provides a nice degree of accuracy for the only 2-3ft of water depth I will be measuring. It is also submersible so the idea is to just use a 1" NPT fitting to drop it into a spare top fitting on my Sumo bags. It is part number PTS-0-1.5PSI-01
Here are some of the technical details on the pressure transducer:
I replaced the metal mounting plate with a 1" to 1/2" NPT plastic adapter from amazon.
This is what the sensor looks like.
I will just drop the sensor with wiring into the top of the bags 1" NPT port. Screw the previously mentioned 1" to 1/2" NPT adapter onto the cable gland that comes with the sensor. Tighten the cable gland on the wire where there is plenty of wire inside the bag for the sensor to stay laying on the bottom of the bag even when full. That is about it for the bag and sensor.
These sensors are typical 4-20mA current loop sensors. So I needed a way to measure these sensor outputs. I decided on 1 Arduino controller with 2 current to voltage converters(1 for each rear bag). The voltage output from the converters will be input into the Arduino on two Analog inputs. These signals then can be sent through the analog to digital converter in the Arduino for use.
The following picture is from testing of the pressure transducer and the current to voltage converter. I just dropped the sensor into about 6 inches of water in a thermos bottle using this setup and measurements were super sensitive.
While I was trying to get the above portions tested out and verify proof of concept, I was trying to decide how I wanted to display this ballast information. My first thought was to go easy and just use a cheap little character LCD. The following was some testing I did that used an adjustable voltage to change the numbers on the LCD. I wasn't super excited about this look compared to everything else in the boat.
After some more time passed, I decided to mess around with a true LCD just because it could look MUCH MUCH better. So I purchased a touchscreen LCD to tinker with. This project probably will never require touchscreen functions, but I went ahead and got one because I could envision in the future creating a bow bag controller using this same screen with some tweaks to show rear and and front bag levels and to also fill/drain the front bag using the touchscreen. That is a project for way down the road. For now, I created a basic UI layout that just displays the rear bag levels in 25% increments. I can tweak this after I get it all setup and decide what works best. I am no Adobe Photoshop guru so I kept the screen designs basic.
For initial setup, I will probably create a screen that shows raw voltages of my bag sensors. I can use that screen to determine exact voltage levels for empty/full/etc.. I can then setup some ranges in the Arduino code to show the correct percentages on the screen based on the inputs. I am planning on making a box to hold this LCD screen and place it in the little cubby hole to the right of the captains chair in a Malibu. I might come up with something better in the future, but this puts it out of the way.
As for the electronics, I purchased a box to mount everything in. I drew most of it up in CAD to test the layout/fitment.
I now have most everything on the box mounting plate. I just need to machine holes for the 3 wires to pass through the box. There will be one 2 wire cable that goes to 12V and ground. There will be a 4 wire cable that exits the box and heads to the rear of the boat for rear bag sensor hookups. There will also be a 12 wire cable that exists to the remote mounted LCD.
I have to finish up the electronics box and the LCD housing box and it will be ready for initial testing in the boat. I hope to have it all ready to go in the boat when the season starts up around here in late March/early April. I am also using a lot of Deutsch connectors with boots, heat shrinks, etc. so I still got a little more to do to get all that wrapped up as well.
I will update this when I get the box all finished up and the LCD housing built. I have had a couple requests to get this posted over here so here it is so far. There are several ways to do this much cheaper than the way I have chosen to do it. The wiring and pressure sensors are definitely on the high end of the spectrum. Feel free to ask any specifics about what I have done so far. I hope to be on the water testing it in about a month...bring on spring!
I got my LCD box back from the 3d printer at the first of the week. A few tolerances were a little tight for the LCD to fit so I had to do some slight machining on a mill today. I kinda expected that as I just had it printed out of ABS using a cheaper printing option so tolerance is not quite as close as for say a SLA 3d print is. The little brass 4-40 press in threaded inserts worked perfectly. I did also make a mistake on two of my LCD hold down holes. I ended up having to remove 2 of the 4. I should still be able to make it work, I will just have to drill 2 holes and make a different tab for one side of the LCD hold down. If you look at the back image of the LCD, you will notice only 2 brass threaded inserts...I had planned on 4 for hold downs. I plan to try to swing by the boat in storage this weekend and double check it will go in the little covey I want to put it in. It will be close. If it fits, I will cut a wire hole in the box and start trying to wire up the LCD. The white paper you see over the LCD is a piece of clear acrylic cut that will be the 'lense' for the LCD for protection. I will glue that in so it is water tight, then put the LCD behind that.
Progress still being made and hope to have it ready to all go in the boat when it comes home for the spring.