Feasiblity - Tachometer + speed meter + flow meter to LCD display


Never did anything with Arduino before and would like some help with a project, please!

I am a computer science student, so I work mainly with software and don’t have a lot of knowledge with stuff like this.

I have to find a way of getting the output of a flow meter, a tachometer and a speed meter, do some math with all that and output a result to a LCD display.

I can handle the flow meter and LCD, but IDK about the speed meter and tachometer.

  1. First of all, as I never worked with Arduino before, I want to know if this is feasible.

  2. I would be using this in a car, how could I get the motor RPM and the speed of the vehicle?

  3. ( image attachment). As I said, I don’t really have experience with this, what does the “at load resistance Min. 10k ohm” means? That would be the flow meter output btw.

Thanks a lot!


what does the "at load resistance Min. 10k ohm" means?

That means if you have a lower resistance than 10K Ohms on the output pin of the sensor, the voltage will be lower.

You don't give us any other information about your application. You can't connect a 7.4V signal directly to an Arduino pin. The voltage needs to be limited to 5V or 3.3V depending on the board you are using. Can the sensor operate on the same voltage as your Arduino? If the answer is no, then you either need a level shifter or a series resistor and a zener diode.

You need to tell us something about the speed meter and tachometer signals, but the same rules apply. Don't let an Arduino pin see voltage higher than it's supply voltage.

Sorry about the lack of info, I searched for speed sensors and haven't found any that I could use, same could be said for the tachometer. I found how to build both using the Arduino board, but I wouldn't be able to build both sensors, connect the flow meter and do the stuff I want with all that. Mainly because this would need to be in a car, so if possible I don't want it to be huge and full of fragile cables.

About the input voltage, in the board specs it is said "By default they measure from ground to 5 volts, though is it possible to change the upper end of their range using the AREF pin and analogReference() function.", I was planning on that, although after reading it again, it doesn't state what would be the upper range then.
Maybe it's easier to change the voltage, how would I do that? Sorry!

*The manual of the flow meter ( I have model 41)


That spec only says "max 45V" so it doesn't tell us what we need to know. They assume you will use their power supply. You can run some tests, but I bet it has more than 2V drop and won't work on 5V or less.

I would put a level shifter or voltage limiter on the signal. I THINK the higher IO voltage allows 5V IO with 3.3V core, but I don't remember exactly. I would be surprised if you could put 7V on the pin without risk.

I am taking a guess that you want to measure fuel flow to the engine in a vehicle. I offer the following thoughts and ideas. Forgive me if I sound preachy.

First, tapping into the fuel line carries a risk of fire. You should not stack up a bunch of adapter fittings to make the connections work. Fuel lines are pressurized. Depending on the make and model they can be medium to high pressure. Diesel injector rails can be very very high pressure.

The sensor in question is an industrial sensor intended for a stationary application. It may not last in the temperature and vibration environment of an engine compartment.

I have seen fuel injector pulses used to measure the fuel flow rate. That way the electrical harness was disturbed, not the fuel system. It was necessary to characterize the injectors to get absolute accuracy.

The 45V is for the Reed Switch, we will be using only the standard MR Sensor, that has a power consumption of "Max. 10mA(Max 0.3W)"

The use would be as you said, to measure the fuel flow in a diesel engine. You raised valid points about the risks, I voiced similar concerns with my teacher some days ago, especially because of the vibrations, but he said that wouldn't be a problem, he already did something similar before so I assume he knows how to handle that.

We didn't think about measuring the fuel injector pulses. He talked with the specific car manufacturer involved and they said it was possible to use the electrical signal from the car tachometer ( it will deactivate the view panel but oh well), I am waiting for the specifics atm, but we will mess with the electrical system anyway so we might as well try to use that. Thanks!
I don't know how injector pulses work but just did some quick research, I think its feasible, but I will have to talk with my teacher about that.

I, too, am against the idea of having a flimsy flow meter involved in the fuel system, specially in the very high stress work situations we are going for, but we are mainly aiming for a crude prototype first just as a proof of concept, so he really doesn't care much about how sturdy this is for now, we will handle that later.

We got another teacher on board that has experience using Arduino, I didn't talk to him yet but I bet he can sort these things now.

Thanks a lot for your help!