Fuel level sensor to protect me from myself. First Arduino project

Question

Im looking for guidance with my first project.

Background for this project.

I have a 100gal diesel transfer tank in my truck. From this tank i have a small 12v pump connected to the fuel tank of my truck, i use this pump to fill my truck on long trips, or if i get into areas where i cant get to a filling station. The problem I have and the reason for this project is the pump is SLOW. That in itself isnt the problem, the problem is that i sometimes forget to turn it off, and yes i have forgot about it long enough to dump 70+ gallons of fuel on the highway ( expensive mistake)

Scope of this project;

I would like to use the fuel sender in the truck tank to turn off/interrupt power to the coil of the relay controlling the pump at a set level ie. 7/8 full. This way I can turn on the switch and if i forget to turn it off i will no longer over fill the truck.

Since this is my first attempt working with arduino im not really sure where to start.

Tomorrow morning I'll be taking some measurments of the fuel sender although im pretty sure it is resistance based.

So i guess the first thing i need help with is interfacing with the sending unit without adversly affecting the guage on the dash.

After this part of the project is complete Id like to also monitor the sending unit in the transfer tank so when that tank is empty ( or at some set point ie. 1/4 tank) also turn off/interrupt power to the coil of the relay controlling the pump so as not to burn the pump out from running dry.

mcb1 · Accepted Answer

Okay

I gave up on trying to use my normal schematic package ... it sucks

Here is the old fashioned version. No guarantees but it should give you a good start point.

I think I've got the logic correct, and I've assumed the sender goes low in resistance when the tank is full.

This is the turn OFF at 7/8th full version.

The LM339 has 4 comparators and they suggest tying the unused inputs to ground.

Using another 1/4 of the LM339 you should be able to duplicate to make the "Turn off at 1/4" but you need to swap the inputs so that the preset part is on the +ve input and the sender part is on the -ve input.

You can add the relay output in series.

The capacitor across the sender should help smooth the fluctuations but will need to be sized according to the sender resistance. I suspect a 1000uF might be needed.

The 1M and 1K for a feedback to stop it oscillating when it's close to the trigger point. I suspect the pump and tube will also give some additional hysterisis so it may not be required.

In theory a couple of LED's (with resistors) at each point in the voltage feed will show the switch is ON, the receiving tank is READY and the supplying tank is OKAY.

You may want to change how the power is fed so that the switch is the final part, that way you can have a LED to prompt you to switch it ON.

You have enough spare inputs to create a third section to prompt you when the tank is below 1/4 ....

Cheers

Mark

mcb1 · Answer

jamesb128 James A simple voltage comparator circuit using an OpAmp will give you all you need. It's late and bed calls but maybe if jw0752 is still up he will have the circuit and have proved it before I can get up. Otherwise I should be able to find something later tomorrow. (ie 24hrs from now) In order to make this work (not matter what system) you'll need to measure the voltage across the senders at the two levels you want it to shutoff at. (7/8ths full and 1/4 empty.) Most fuel guages are powered by a regulator in the dash so they receive 8v or there-abouts to keep them stable. You'll probably want to do the same for your transfer tank guage. I encourage you to try many of the examples that come with the Arduino IDE and get used to buttons and controlling outputs. I prefer to pull the input down to ground which then sets you up for these sorts of interfaces. I get the pupils to try two buttons and two leds. After they turn each led on with each buttn, change the software so the first button turns on the first led, second button turns off the first and turns on the second led. Reset to return to both leds off. It's an exercise in understanding what you have and the end goal. Your learning can then be transferred to your next (or this) project. Mark

mcb1 · Answer

jamesb128 Welcome to the world of electronics, and Arduino. Before you start you're going to have a couple of problems. 1. The sender and guage are 12v (or 24v) which is incompatible with the 5v of the Arduino. 2. The extended wiring is quite likely to be subjected to interference unless you are very careful. I suggest the old fashioned method of using some basic electronics and a couple of relays. The voltage across your existing fuel guage is compared with a set voltage, and the output drives a relay that allows power to go to the pump. When the voltage across the sender rises (as the tank fills), it reaches the set point and the relay interrupts the power, thereby stopping the pump. The simplest method I know of monitoring your second tank level is another sender and guage from a donor vehicle. These are rugged and can be secured into the tank from the top, like your existing vehicle. You can duplicate the electronics and use this to also provide power to the relay when the tank is above the set point. I'm all for microcontrollers but sometimes a simple bit of old fashioned electronics goes a long way. In the meantime measuring the voltage across the sender at your desired "full" point will help with whichever methd you choose. Mark

dougw · Answer

Nice project. (But why use an arduino? it seems the pump could be interrupted directly by the level sensor - no programming needed....just a little hysteresis)

Fuel level sensor to protect me from myself. First Arduino project

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