G.9.1) Fuel Flowmeter

This is what I have been trying to achieve with a Propeller protoboard, a Parallax Micro SD card interface, Parallax GPS and a bunch of LED's and switches.

The aim was to have a means of monitoring the fuel remaining in my boat and to gain an understanding of how fuel burn changes with speed and load. It is not supposed to be highly accurate, but to help planning and economy whilst giving an idea of when I need to change tanks.

Proprietary fuel monitoring systems are expensive and I wanted something to log data so that I could characterise the boat and engine given the number of passengers, etc., It doesn't however, take trim position or loading into account, so it won't be perfect. I have a 11 yr old son who likes to tootle along at no more than 10 mph (at which speed the boat is mushing through the water in a very inefficient way) and his 9 yr old sister who goes everywhere at 40kts - there must be a 'best range' speed between these two extremes.

 Using flowmeters inevitably means possible exposure to a highly flammable atmosphere. Even 12 V is enough to result in a spark sufficient to ignite that vapour.

What it does:
  • The user can set the initial contents of the fuel tank in 1 litre increments.
  • The user can set the number of passengers present (a rough indicator of 'dry weight').
  • The user can move between the various screens at will, or the code will bring up the relevant screen in the event of an alert.
  • One of the eight Propeller 'cogs' sits there and only waits for the pulses from the flow sensor. When a pulse occurs it increments the 'fuel consumed' data and decrements the 'fuel remaining' data.
  • Using the Propeller counter as a time reference, the rate of fuel consumption is calculated and displayed.
  • GPS position and other data can be shown to the user.
  • GPS position, fuel quantity and GPS speed are logged to the SD card at 1Hz, for subsequent analysis in slow time.
  • The LCD is a transflective type that is visible in bright daylight. Its all crudely stuffed into a crudely waterproofed box.

The code and a calibration constant are installed on the SD card, making it possible to update the code without taking a laptop to the boat. The calibration constant matches the sensor to the software. With the flow sensor I am using one pulse is nominally created for every 0.4 ml of fluid - a calibration constant of '394' (i.e., 0.394 ml) has been found to match displayed used volume with actual volume for 25l of water.

Using three digits for the constant allows for quite a bit of fine tuning.