I decided to make a digital indicator of the amount of fuel for a truck (bus), using a standard (rather mediocre) fuel level sensor...

Read the entire creation process and what came out of it in the article below.

Initial conditions:

• Truck (bus) with on-board voltage 24v
• Fuel tank for diesel fuel on 220l
• Fuel level sensor DUMP39
• Fuel level indicator EI8057M-3

Need to:

Make a digital fuel level indicator using a standard level sensor.

First, you will have to carefully study what a standard fuel level sensor, called a fuel level sensor, is. Let's dismantle it and examine it carefully.

As you would expect, there is a float, a rod, a variable resistor... wait, more about the variable resistor. As they say, it is better to see once than to hear a hundred times:
The design is both logical and clumsy. It is logical that the slider slides not directly over the variable resistance (which is quite delicate), but along the metal taps from it, but for such an increase in reliability you have to pay for discreteness. The clumsy thing about this design is that, as can be seen in the photo, in the middle position of the float we have a fairly large “dead zone”, due to the very wide central outlet from the resistance. Why this was done, we can only guess, but what we have, we will have to work with.

So, we rummage through the Internet and look for information. Here's what I dug up:

Float movement range - 412mm

Nominal resistance - 800 Ohm (according to another source, the nominal resistance is 761.0 – 193.5 Ohm)

Operating range from -40°С to +60°С

MTBF - 400 thousand. km to 95% wasting resources

Weight 160 gram, analogue - MAZ.

In general, not a lot.

We take the tester and measure it, and in the end we get the following picture:
Connection diagram:

Measured sensor parameters:

Total resistance - 767 Ohm

Additional resistance - 187 Ohm(it provides the minimum sensor resistance).

Left (from the photo) part of the resistance - 203 Ohm (13 taps to the slider), right side Ohm 376(17 taps to the slider).

Two metal sectors above the contact group - the left sector is not used, the right one goes to the fuel reserve lamp.

In general, I am giving such a detailed description only for those who are curious; we need the voltage value that we have at the output contact at different fuel levels. With the extreme left position of the contact at the output, we got 1.57v, at the extreme right position 3.28v, half a tank - 2.44v. At the beginning of the sector of switching on the lamp of the remaining reserve 2.95v.

More for the curious. The general connection diagram for the fuel level sensor looks something like this:
Reels L1A, L1B, L2- this is a deflection system of the fuel level indicator (essentially a milliammeter). The resistor is thermal compensation.

In fact, this is a diagram of a classic electromagnetic automotive device, specifically EI8057M-3- this is something else: there is an electronic circuit inside, the arrow is driven by a stepper motor, and all this is controlled using a microcontroller PIC.

In principle, this is enough to calibrate a digital indicator, if not for a couple of troubles:

1. Specified fuel tank capacity in 220l not true, in fact the tank holds more fuel.

2. In the extreme right position of the movable contact of the sensor, when there is supposedly no more fuel in the tank, in fact the float should already be below the tank level, which is, of course, nonsense (determined by the geometry of the tank and the fuel level sensor.

3. Having measured the geometry of the tank with a tape measure, we are convinced that it is a rectangular parallelepiped with slightly rounded long edges, dimensions 40x112x60 cm. Multiplying the sides accordingly, we get an internal volume of 268 liters, which, you see, is very different from the declared 220 l, and it is very doubtful that the internal partitions, mesh, fuel intake, etc. occupy almost 50 l.

4. As already written above, the resistance of the sensor over the length of its resistance is nonlinear.

What we do:

Fill the tank full and control the voltage at the FLS output. It turns out that after reaching the mark 1.57v The tank still contains a good twenty liters of fuel.

Remove the float and put the sensor in place. Naturally, the draft, devoid of a float, goes to the very bottom of the tank, look at the voltage - it is 3.02v! This is important because in fact, in this position there is no longer any fuel in the tank, and the moving contact has not yet reached the extreme position in 3.28v, while the standard device EI8057M-3 shows what's left in the tank 1/8 volume. (Putting the float in the central position, at standard EI8057M-3 we observe instead of the required ones 1/2 tank as much 5/8 level, with a full tank the standard device goes off scale).

We look at the graph of our fuel level sensor,

Let's take three points - the resistance of the sensor, the first point is its lowest resistance (moving contact on the left) formed by additional resistance in 187 Ohm(in the photo there is a vertical black rectangle), the second point at the middle position of the contact when connected in series 187 Ohm And 203 Ohm, i.e. 390 Ohm, the total resistance will accordingly be 390 + 376 = 766 Ohms.

(horizontally - resistance in Ohms, vertically - conventional units of length)

There is nothing pleasant in this picture; the sensor seems to be linear but has a significant kink.

With such a picture, we will either get accuracy in the middle, or at the ends of the broken line, or something in between by approximating:

Having received the formula with the correction and coefficient, you can, in principle, make something similar to a digital fuel level indicator, coefficient R 2 trend lines in 0,97 Of course it’s not bad, you can, in principle, use anything greater than 0.95.

But you can get your own conversion factor for each line, which will be more accurate:
We immediately measure the ADC value at the points we need so that 5% The tolerance for the divider resistors at the ADC input did not spoil anything for us and we get it in the range of an empty tank (ADC822) before 1\2 tank (ADC700):

(horizontally the received ADC readings, vertically the volume of fuel in liters)

Ranges from 1\2 tank (ADC700) to full (ADC456):
From the above we have the following:

1. As the amount of fuel increases, the resistance of the sensor decreases and the voltage drop across it decreases.

2. The sensor voltage delta is 1.45v, that at 10 bit ADC will be 56% which is more than enough to scale the ADC result to scale 0....220l and will allow you to simply digitize the result without using OU to adjust to the desired voltage range.

The scheme is incredibly simple:

Microcontroller Mega8, LED indicator on 3 discharge with a common cathode, input divider of two resistors R1, R2. Zener diode (in bourgeois zener "zener" diode :)) to protect the input MK just in case. I didn’t draw the power circuits, they are classic 0.1uF ceramics and some kind of electrolyte 100...1000uF as well as quenching resistors between the MK and the indicator, any in the range will do 80...100Ohm depending on the MK supply voltage and the brightness of the indicator. The voltage on board the car with the engine running was 27.5v.

My board layout:
On the right side of the board I placed a power converter that provides 5v at onboard voltage 10...30v the converter is assembled on MS3406 3 according to the typical diagram from the datasheet. throttle murata 1812. The zener diode indicated in the diagram is 3.3v I screwed up when wiring and soldered on top.

Why did I apply Mega8 when there is a much more convenient one Tiny26 and so on. ? because Mega 8 available 1kB RAM, why so much? The microcontroller not only measures the voltage at the input and displays the recalculated value on the indicator, it constantly records the measured values ​​in one of 256 memory cells, filling them in a vicious circle and after recording each cell, it calculates the average value over all currently available 256 cells.

The indicator is located outside the board on the car's dashboard and is connected to it 11 wire loop. The board is placed in a tiny case (the second one, the one with 4 wire terminals); excess plastic was removed from the case with side cutters.

The board is single-sided, without jumpers:

First, I unsoldered the PWM switch and checked the work, it works. varnished. you can continue building:

P.S. The project was created with the enormous support of Roman Viktorovich, for which many thanks to him, also thanks to the man Johnson from Ukraine for mathematical help and some ideas.

The fuel level sensor in a car is a controller designed to monitor the volume of fuel in the tank. Its presence allows the car owner to fill the tank in a timely manner so that there is no stopping on the road while driving.

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Fuel level sensor device

Gasoline or diesel fuel level meters in cars are divided into two types - lever and tubular. Depending on the type of fuel controller, its design and operating principle will be different. Digital or electronic sensors are practically not used on modern cars due to the fact that they are characterized by low accuracy.

Lever

The main components of a lever-type fuel level sensor in a vehicle:

• potentiometer;
• float;
• lever element.

The potentiometer itself includes two sectors. A plate made of resistive material is applied to one of the components. The second sector is a slider that is in contact with the plate and lever. The other part of the part is connected to the float.

Tubular

Tubular parts have differences in terms of structural components. Such controllers are not equipped with potentiometers, but they use its principle of operation.

The main components of the device:

1. Protective tube.
2. A guide component is installed in the tube itself.
3. A float that moves along the stand.
4. Looped resistance conductor. This component is connected to electrical circuits that go to an indicator located inside the car on the dashboard.
5. Contact rings. They are located inside the float. These elements are always in contact with the electrical circuit, which makes it possible to additionally loop the resistance circuit.

Monitoring control systems

A controller connected to a monitoring system is the most effective option for checking fuel consumption and tank volume. Such systems have the ability to obtain data on vehicle mileage, which is important for commercial vehicles. Information about mileage is instantly transmitted to a remote control panel. This suggests that if you have data about the car, you can use a special formula to calculate the amount of fuel consumed.

The main disadvantages of such systems:

1. The cost of efficient and high-quality systems is usually high. If the machine is equipped with a diesel engine, then at least two flow meters will have to be installed on it.
2. Difficult to install. To install, the consumer will have to insert the devices into the fuel line and other elements of the car system. It is almost impossible to complete the task on your own; you will need the help of qualified craftsmen. You will also have to pay for this.
3. High sensitivity of monitoring flow meters to low negative temperatures. If the viscosity of the fuel is increased, then the operation of the power unit will be impossible as a result of the fact that the fuel will not be able to pass through the flow meter.
4. The device is equipped with an input filter element. This component can become clogged with regular use of the car and refueling it with low-quality fuel. Foreign particles and dirt settle on the filter. As a result, the passage of fuel becomes difficult and monitoring of consumption is impossible.

Operating principle of the sensor

The operating principles of different types of devices differ.

Operating principle of a lever-type sensor

The float, made in the body of a hollow sealed component, is always located on the surface of the fuel. The device itself can be made of plastic or metal. When fuel is consumed, this component is lowered, and as a result of the action of the lever, the potentiometer slider moves.

The float is in contact with the sectors to which the conductors are connected. The latter are connected to the fuel indicator located in the dashboard. As a result of changing the number of plates connected to the potentiometer circuit, the resistance value changes.

When the fuel tank is full, the slider is set to the extreme position; accordingly, the current flows along the shortest path in the potentiometer. Current transmission is carried out on the sector through a plate located at the edge. Therefore, the resistance value is quite low and is about 7 Ohms. When the fuel is consumed, the slider of the device moves, which contributes to the addition of new plates to the electrical circuit, because of this the resistance value increases. If the tank is half full, the resistance value is about 120 ohms.

The GLONASS monitoring channel Fuel control showed the nuances of using monitoring systems.

If the tank is completely empty, then the plate part of the system is fully activated. Therefore, the resistance parameter will be as high as possible and will be about 330 Ohms. All described resistance values ​​are approximate, since different controller models have certain parameters.

The main advantage of a lever fuel level sensor is the simplicity of the device, due to which such controllers are considered reliable. Their price is low. The main disadvantage of the lever controller is the wear of the contact component. In addition, such sensors have a certain error in values, in particular, we are talking about machines equipped with analog controllers.

Operating principle of a tubular sensor

The operating principle of tubular devices is somewhat different. Fuel passes through the technological hole located in the lower part of the device into the protective pipe. A float is located on the surface of the fuel. As a result of changing the position of the element with an increase or decrease in the volume of fuel, the resistance value changes.

When the vehicle's fuel system reservoir is full, the float is located on top of the safety tube. As the volume of fuel decreases, the float drops and the length of the electrical circuit increases, which leads to an increase in the resistance parameter on the wire section.

Why might it not work?

Fuel level controllers in the tank often break down, causing car owners to face problems. The parameters on the control panel are displayed incorrectly or are missing altogether. All device malfunctions can be divided into mechanical and electrical.

When it comes to power line faults, everything is simple – the problems are a consequence of:

• oxidation of contact elements;
• failure of safety devices;
• power line damage.

The AvtoTechLife channel, using the example of a Chevrolet Niva car, offers to learn about the nuances of diagnosing the electrical component of the FLS.

Mechanical problems can be more serious:

1. Failure due to wear of the working sectors of the potentiometer. Wear of the elements occurs due to the contact of the potentiometer with the slider, since the latter regularly moves through the sectors. If the wear is insignificant and there is only a worn strip on the sector, then to eliminate the problem you can bend the slider. This will cause it to come into contact with the unworn part of the sector. However, if the wear band is wide, this will not give results and the controller will need to be replaced.
2. Bend of the device lever. A malfunction usually occurs as a result of removing the controller and then installing it, during which errors were made. As a result, the controller works, but when displaying readings, incorrect values ​​will be displayed. The deviation can be serious.
3. Damage to the float due to leakage. A malfunction will result in fuel getting inside the controller, so the device will always be located on the surface. When the volume of fuel in the tank increases, the sensor will be immersed in the liquid. The values ​​displayed on the dashboard will be incorrect.

Problems of this kind will lead to complete failure or incorrect functioning of the controller. The arrow on the control panel may twitch during operation or indicate an empty fuel tank.

If problems with the fuel level sensor are related to a mechanical component, then it is advisable to completely replace the device.

Signs of trouble

You can determine a malfunction in the operation of the controller through diagnostics; to do this, you need to know the signs of the problem:

1. The indicator needle on the dashboard fluctuates constantly.
2. The controller needle is located in the zero position when the tank is full. This indicates that the device's travel stop is in the wrong position.
3. When the ignition is activated, the indicator needle on the dashboard does not move. This symptom usually indicates a burnt-out safety device or a problem with the electrical circuit.
4. The pointer needle jerks and always falls to the zero position. The reason may be a poor-quality connection between the contact element of the potentiometer and the current collector. If the sensor is repaired independently, then the integrity of the potentiometer winding is diagnosed.
5. The indicator light has stopped working, indicating that the fuel level is low. The likely cause is a malfunction of the potentiometer.
6. Incorrect indications about the fullness of the fuel tank.

The Auto Electrician HF channel spoke about the nuances of checking the controller pointer arrow.

Replacing the device

You can connect and install the fuel level sensor yourself. Even an inexperienced car owner can cope with this task, provided all conditions are met.

When replacing the fuel level sensor, you must focus on the electrical circuit parameters that are indicated in the service documentation for the machine.

How to remove the fuel level sensor

The procedure for removing the device will have certain features depending on the machine model. If the device is installed in a fuel pump, it will have to be removed from the unit after removing the latter.

Dismantling the controller looks like this:

1. In cars equipped with gasoline engines, the negative terminal of the battery must be disconnected before removal.
2. The next step is to provide access to the controller. Here you need to focus on the installation location of the device. It will be necessary to remove the decorative lining of the luggage compartment or dismantle the rear seat. To do this you need a set of screwdrivers and wrenches.
3. Fuel level controllers can be equipped with a safety plate located on the top of the device. To dismantle this element, you need to unscrew the screws that secure it.
4. The next step is to clean the controller and the reservoir surface around the sensor. It is necessary to remove all dirt and dust, which will prevent possible dirt from getting inside the tank.
5. Then the connected electrical circuits are disconnected; when performing the task, they should be marked so as not to be confused when connecting.
6. The screws securing the device to the fuel tank are unscrewed. The controller is carefully removed, all actions are performed carefully to prevent damage to the device. If the sensor is located in the fuel pump, then the unit will have to be disassembled or the top cover removed from it in order to remove the meter itself.

How to install?

Installing the controller for measuring the fuel level is done as follows:

1. Before the installation procedure, the seat is cleaned and the remaining sealing adhesive must be removed.
2. If the controller package includes a gasket, it is installed in the device’s mounting location. The seal must be treated with airtight glue, if necessary. This will ensure high-quality sealing. When installing the gasket, it is important to align the holes for the screws that secure the device.
3. The assembly procedure is performed in reverse order.

Connection diagram

Universal card for connecting FLS in a car

How to check the functionality of the sensor?

Before installing the seats and luggage compartment trim, it is necessary to diagnose the correctness of the measures taken:

1. When the assembly procedure is completed, you need to diagnose the parameters on the controller located on the dashboard. To do this, you can fill the tank and make sure that the arrow on the dashboard sensor has risen.
2. Then you need to drive about 30-60 kilometers. After the trip, access the controller in the tank. Make sure there are no fuel leaks or smells.
3. All remaining interior components can then be assembled.

DIY repair

If the sensor is equipped with a porous component, there are several options for changing it:

1. You can remove it from the retainer socket and install a new one, securing it.
2. Or replace the float itself along with the rod.

The second option is more preferable because it is easy to implement. If the surface of the strip on the rheostat scale is dirty, the element is cleaned.

The cleaning procedure is performed exclusively with cotton wool or a soft cloth pre-treated with alcohol. The use of harsh materials or other products is not permitted. This will damage the working layer of the scale; it is quite thin, so it can cause the rheostat to break. The element cannot be repaired; it will have to be replaced.

If the contacts of the electrical circuit come off the controller, they must be carefully soldered back or connected at the point of damage. Plates with mechanical damage (cracks, fractures) cannot be repaired, only replaced. If the sensor gives incorrect readings, the problem can be corrected by adjusting the angle on the so-called rod. This element is designed to fix the float. To get accurate readings, the angle is bent in different directions.

How much does a fuel level sensor cost?

The cost of the device depends on the manufacturer and the specific car model.

Video “Example of diagnostics and repair of a controller”

Pavel Cherepnin clearly reported on all the features of checking and repairing the fuel level controller in a car.

Revealing the internal aspects of production and work in general. In this article I want to talk about the full production cycle of such a very important element of GPS monitoring and control systems as a fuel level sensor (search engines know it as FLS). There will be a theory, all the drawings and diagrams for assembling this product. For those interested, read on.

0. Introduction

Looking ahead, I will say that there will be three articles, in this one I will talk about the simplest option for determining the level of diesel fuel (diesel only, use on gasoline vehicles is absolutely prohibited, as it is explosive). In the following articles, if of course the reader is interested, we will consider a digital fuel level sensor, and at the very end I plan to post the circuit diagram and firmware of the monitoring device that I described in this article.

1. A little theory

The most popular fuel level measurement sensors are an electric capacitor consisting of two tubes placed inside each other; a tank with fuel is installed, the level of which is measured. Diesel freely penetrates into the space between the tubes; a change in the fuel level in the tank is signaled by a change in the electrical capacitance of the sensor.

When the fuel level in the tank changes, the relative dielectric constant of the space between the capacitor plates changes, since the dielectric constant of fuel and air are generally different. And since the capacitance is directly proportional to the dielectric constant of the insulator, the electrical capacitance of the sensor also changes as a result. Sensors are mostly made of aluminum or copper because they are least susceptible to aggressive environments. Of the many ways to measure the capacitance value of a capacitor and then convert its capacitance into a proportional change in the DC voltage at the output, the pulse-width method was chosen as quite simple and reliable, but at the same time providing the necessary level of measurement accuracy. A disclaimer is immediately required, this is the simplest method in terms of finances and quite simple in terms of assembling the FLS method for determining the level of diesel fuel.

2. Description of the operation of the electrical circuit of the fuel level sensor

Fig 2. Schematic diagram of the fuel level sensor (FLS) ()

To increase the stability and accuracy of readings, all circuit elements are used with a minimum temperature coefficient. Resistors are used with a 1% tolerance, microcircuits are selected with improved parameters in contrast to household analogues, for example: SE555N instead of NE555N, and LM358D instead of LM258D.
A master oscillator is assembled on the U1 SE555N chip and elements R1, R2 and C1. Since the stability of the reading greatly depends on it, a precision polystyrene capacitor K71-7 1% is used as capacitor C1; they were usually installed in Soviet color TVs as master horizontal oscillators. It can be replaced with something modern, but the availability and price of these capacitors makes them very attractive, and they were born back in the distant year, when the USSR was very good at monitoring the quality of the elements produced.
From the output of the 3rd microcircuit U1, rectangular pulses trigger a one-shot device assembled on the U2 SE555N microcircuit. As a single-vibrator capacitor, a sensor placed in the fuel is used, so its capacity will depend on the fuel level, and therefore, the pulse width at output 3 of the U2 microcircuit will also change on the fuel level.
To ensure a linear dependence of the pulse width on the level of fuel filling of the sensor, the fuel sensor receives charging current from a current stabilizer made on the U3.2 chip and transistor Q1 BC856BT. Also, by changing the charging current, the circuit is adjusted to different sensor sizes. The circuit is configured by selecting resistors R6 and R7 to obtain 1.8-1.9 Volts at the output of the circuit, with a “dry” sensor.
From output 3 of microcircuit U2, pulses are sent to an integrator assembled on elements R8 and C6.
Next, the integrated voltage formed on capacitor C6 is supplied to the low-pass filter made on R10 and C10.
Then the constant voltage is supplied to the direct current amplifier, made on the U3.1 chip.
From the output of the 1st microcircuit U3.2, the signal, through a filter made on elements R17, C12, C14 and C15, goes to the output.
Resistor R16 is used to prevent self-excitation of the amplifier when operating a capacitive load.
The divider is made of resistors R9 and R11 and provides the necessary constant bias for the DC amplifier to operate in linear mode.
The voltage stabilizer for powering the electronic circuit is placed according to the classical circuit on the U4 LM317MDT chip.
As a result, at the output, we receive an analog signal empty tank 1.8V full 6.0V (there is a dependence on the height of the FLS), which is linear and directly proportional to the fuel level in the tank\tank\storage. Then, using the Kalman filter, you can remove fuel surges, calculate the average consumption, etc.

In reality it will look something like this:

Fuel level graph + speed.

3. Drawing of the fuel level sensor, materials

FIG 3. Drawing of the fuel level sensor (link to large drawing)

It has already been mentioned that aluminum is mainly used, as can be seen from the drawing, the outer tube is soldered in any convenient way into the “head” of the FLS. When producing our sensors, we use welding, because... we have access to it, although not the most aesthetically beautiful option, but it is reliable and time-tested. An aluminum rod is used inside, to fix which a thread is cut in the upper part. The bushings are made of special fluoroplastic, which is maximally tolerant of diesel fuel.

4. Summary

The vast majority of fuel level sensors presented on the GPS market in the CIS and around the world are built on this solution. Each manufacturer makes its own changes to increase the accuracy of fuel level measurement, such as an accelerometer, temperature sensors, digital signal processing, etc. The scheme I presented is the simplest, ready to work, as they say, in the fields without any difficulties. Dear reader with straight hands, it is quite possible to make any modifications that can be used both for your own purposes and for commercial needs.

PS. A little erotica about how such goodness can be installed on equipment.

Published 09/25/2012

Knowing the fuel level in the tank is not only “cool”, but sometimes vital. In some cases, it is difficult to assess the fuel level in the tank due to its location or lack of transparency. For such cases, there are fuel level sensors. Today, float sensors are the most common. The operating principle of such sensors is quite simple. The float mechanism, depending on the fuel level in the tank, changes the position of the moving contact of the potentiometer. The voltage reading on the potentiometer is measured and converted into human-readable form. However, it is not always possible to install a float sensor due to its size. In addition, in devices where roll is a normal condition, for example, ultralight aircraft, the float mechanism may become skewed and jammed. In addition, the position of the tank in the ground and flight positions may differ, which may alter the operation of the float mechanism. However, there are other ways to measure fuel level. I'm talking about capacitive fuel sensor. It is especially relevant if there is a need to get rid of moving parts.

Measuring principle and features

This method is based on measuring the electrical capacitance of the sensor, which, in turn, depends on the fuel level. The sensor used to measure the fuel level is called a capacitive fuel level sensor. The design of the sensor is quite simple and is nothing more than a capacitor. It consists of two plates, between which there is a gap that can be filled with fuel. The sensor can be made in the form of two metal plates or tubes inserted into one another. In this case, the surfaces of the two electrodes (capacitor plates) should not have electrical contact, and the gap between the plates should be freely filled with fuel when the sensor is immersed and just as freely released when the fuel level decreases. As fuel fills the space between the plates of the capacitor (sensor), its capacity changes. This method is only suitable for liquids that do not conduct electricity. This method will not allow you to measure the water level. Gasoline and other types of liquid fuels do not conduct electricity. By measuring the electrical capacitance of the sensor, you can estimate the fuel level in the tank. I would like to draw attention to some of the disadvantages of this measurement method. The fact is that the dielectric properties of the fuel can change when the chemical composition of the fuel changes. Those. When changing fuel type, you may have to calibrate the device. Despite this, this method allows you to install the sensor in the tank at an angle, or even mount it in the tank filler cap. The sensor has no moving parts, which is extremely necessary in some cases.

Is it safe to place an electrical circuit in a tank? Many people are concerned about this issue. What if there is a spark? Our sensor circuit is powered by a voltage of 5V, and the sensor is charged through a resistor of several megaohms. Under these conditions, spark formation is impossible. A voltage of 5V is negligible to cause a breakdown spark. In addition, an electric fuel level sensor already “floats” in the tank of any car. Low voltages and currents cannot cause a spark and ignition of the fuel.

I did not set myself the task of obtaining a super accurate sensor capable of measuring the fuel level to within 1mm and with an error of 0.1%, although this is quite possible. Considering that the sensor was created for devices where the fuel in the tank will be mobile, we are quite happy with a budget option with an error of 5%.

The sensor module circuit is based on measuring the charging time of the sensor. The higher the fuel level, the higher the sensor capacity, the longer it will take to charge the sensor (capacitor). The scheme works as follows. Uses built-in microcontroller ATMega8A analog comparator.
To the comparator input PD7 half the supply voltage is supplied through a resistive divider R3,R4. At the moment when the sensor is charged to this voltage, the comparator will operate. On the foot PD6 logical is set «0» . The sensor is discharged through a resistor R2. After which exit PD6 switches and works as a comparator input, the timer starts, and the sensor begins to charge through the resistor R1. When the voltage set at the input is reached PD7, the comparator is triggered, the timer stops. The timer readings are used for calculations. To ensure stability, the microcontroller must be clocked with quartz. The higher the frequency at which the controller operates, the higher the measurement accuracy. In our scheme ATMega8A clocked by quartz 16MHz. Measurements are taken continuously, averaged, and sent once per second via the serial port UART at speed 9600 as a numeric value. This is where the functions of the sensor module end.

As a sensor, I used two strips of foil PCB 1.5 mm thick with dimensions: 290 × 20 mm. The strips are glued together foil to foil through small non-conductive spacers. The distance between the plates is 1.5 mm. They can be made to almost any length. You can trim it if necessary. It is especially important to ensure a uniform gap between the plates along the entire length of the “capacitor”.

The display module is responsible for displaying the data received from the capacitive sensor module. This module can be designed according to your requirements. Data can be displayed on an LED bar, on a display, as in our case, on a dial indicator, or any other display device. If necessary, the sensor module can be connected to a computer via an adapter.

The display module works as follows. Numerical data is received from the sensor module via the port UART at speed 9600 , fuel level readings are calculated and displayed. But in order to perform a correct recalculation, the display module will need to know at least two sensor values ​​- the numerical reading of the sensor when the tank is empty and the numerical reading of the sensor when the tank is full. To do this, after installing the sensor, the device calibration procedure is performed. The display module remembers the readings when the tank is empty and full, stores it in its non-volatile memory and performs a recalculation in accordance with these data. Since the module does not require special performance, its microcontroller ATMega8A operates on frequency 2MHz from the built-in RC oscillator.

Instrument calibration procedure:
- the fuel tank must be empty, the device must be turned off
-press and hold the button
- turn on the power of the device
-release the button
- “SET 0” will appear on the screen. Make sure the tank is empty and press the button.
- “SET 100” will appear on the screen. Fill the fuel tank full and press the button.
- calibration is completed.

PCB example:

Sensor module board

What to do if the fuel level sensor in the tank shows incorrectly, is buggy or lying? Of course, immediately repair it or replace it with a new one, since this device not only predicts our fuel costs, but also saves the family budget by controlling its consumption.

Basic functions of the device

All capacitive fuel level sensors are designed to measure the amount of liquid in a container, or more precisely, in a gas tank. They are connected to the vehicle monitoring system, to which they transmit the corresponding signals. Basically, these are high-precision universal devices that can be used not only for cars, but also for other equipment, as well as stationary objects.

Today there are several types of this mechanism. And it doesn’t matter at all which fuel level sensor (float, electronic, digital, ultrasonic, universal) was chosen, its main function still remains the same - determination. But it is the costs of fuel that are the most constant and most significant for the pocket. Also, the gasoline level sensor will allow you to control such issues as fuel drainage (this function is especially important for enterprises, taxi services, etc.), and, of course, will prevent you from being fooled at the gas station.

For more detailed monitoring of fuel levels, you need to install more sensitive devices with the smallest error on your car.

Operating principle of the device

Basically, the design of the fuel level sensor requires the presence of a float. Most often, it is made of plastic, foam or other lightweight material. The presence of a potentiometer is also important; its role is played by a resistor, on the surface of which metal strips are applied, and its moving contact creates variable resistance to the current that passes through it.

Today, the most popular are tubular or lever-type potentiometric sensors. The principle of operation of the first type of fuel level sensor is that a float placed in a tube moves depending on the position of the liquid and closes the wires located parallel to the guides. In the second case, the movable contact of the potentiometer is connected to the float via a metal lever.

Possible problems with the gasoline level sensor

Problems with the fuel level sensor are of various types. The most common problems are related to the fact that the device shows unreliable data, for example, its arrow indicates that the tank is empty, but in fact there is still plenty of fuel in it. And there are quite a few reasons for this behavior, for example, the panel itself may fail, or it is possible that the arrow is out of order, or the float is jammed.

When the readings of the device fluctuate: for example, at the beginning of the movement it indicates the minimum fuel level, but then this value increases on its own, then this also indicates that the device is not working, but how to check and repair the fuel level sensor in such a situation , we will describe below. If the light on the panel, warning about the minimum amount of fuel in the tank, stops lighting up, or it works, but is faulty, then the whole point is the thermistor, which must be replaced immediately.

We repair the fuel level sensor ourselves

But before you begin direct replacement or repair work, you need to know where the low fuel level sensor is located, how to remove and repair it. It is attached to the gas tank from below, and therefore, in order to remove it, it is advisable to jack up the car and disconnect the contacts. First of all, we pay attention to the condition of the paths, since they are often erased from the impact of the runner. If the defect is small, then you can bend the slider so that it is above the damaged area. If this cannot be done, the entire device should be replaced.

Also, checking the malfunction of the fuel level sensor involves diagnosing the contacts and the “ground” (especially that located under). To get to the contacts, you need to remove the panel and then tighten all the nuts, through which the short circuit is created. If the arrow indicating the fuel level is out of order, then you need to press the daily mileage button and then start the engine.

But besides information on how to repair or replace this device, someone may be interested in how to fool the fuel level indicator sensor. One way to drain gasoline unnoticed is to install a so-called dropper, because this device records only those drains that occur in a very short time interval. But if the liquid drips slowly, then such a scam will not be detected. In general, repairing and replacing a fuel level sensor is a simple operation, so it is not at all necessary to contact specialists for this, but you can do most of the work yourself. It is much more important to choose a truly high-quality device.