The HX711 Arduino is one of those chips that seem simple in theory but, in practice, can take up more than half the project. On forums, it all looks straightforward: connect four wires, load the library, and you’re done. In reality, the first meaningful reading often only appears after several hours of battling drift, noise and ‘random’ values.
The problem doesn’t lie with the circuit itself. The HX711 works exactly as it should. The trouble starts when you treat it as a standard ADC rather than a measuring component designed to handle very small signals. If you understand what it actually does and what it needs, most of the problems disappear.
Why isn’t the HX711 ‘just another ADC’ for Arduino?
Arduino has analogue inputs, and many people try to compare the HX711 to these. This is a mistake right from the outset. Arduino’s analogue inputs operate in the range of volts and have limited resolution. A strain gauge, on the other hand, generates voltage changes in the order of microvolts, which is several orders of magnitude smaller.
The HX711 was designed specifically to solve this problem. The circuit features a high-precision differential amplifier and a 24-bit analogue-to-digital converter. It first amplifies the signal from the strain gauge bridge and only then performs the conversion. The Arduino receives digital data rather than barely measurable voltages.
That is precisely why the HX711 is the standard choice for projects involving weight, force or pressure measurement. Not because it is the cheapest option, but because without such a sensor, the Arduino simply cannot detect what is happening in the strain gauge.
What does the Arduino HX711 actually measure, and why is it so sensitive?
The HX711 does not measure mass or force. It measures the voltage difference across the output of the Wheatstone bridge. All interpretation of this data takes place within the software. From the circuit’s perspective, every minute movement, vibration or change in temperature represents a real change in the signal.
This explains why projects using the HX711 respond to:
- touching the structure,
- displacement of the cables,
- a change in room temperature,
- unstable power supply.
The system doesn’t filter the world. It observes it very closely. If the mechanics are not rigid and the electrical signal is clean, the HX711 will show this mercilessly in the form of ‘floating’ results. This is not a measurement error. It is information. That is precisely why a stable design with the HX711 begins not with the code, but with the mechanics and the power supply. The software can only improve what already exists at the input.
HX711 modules on the market and their practical limitations
Ready-made HX711 modules available from electronics retailers are convenient and inexpensive. They contain everything you need for initial testing: a sensor, a voltage regulator, connections for a strain gauge and communication pins. They allow you to quickly validate your design concept.
However, it is important to bear in mind that these are compromise modules. The quality of voltage regulation can vary, power supply filtering is often minimal, and the ground connection is not always suitable for measurements of such low amplitude. In simple applications, this is sufficient. In more demanding projects, however, things start to get tricky.
That is why two identical designs can behave completely differently, despite having the same code and the same strain gauge. The difference lies in the details: the length of the cables, the way they are routed, the quality of the power supply and the rigidity of the mechanical structure.
The first meaningful reading is not yet a measurement
The moment numbers appear on the serial port monitor can be misleading. Many people then assume that it is ‘working’ and move on. However, the HX711 can very easily give the illusion of functioning correctly. The device reacts to everything: pressure, touching the table, movement of the cable, changes in hand temperature. These are not errors. This is the raw signal.
That is why the first step when working with the HX711 is not to take any measurements, but to check how the circuit behaves at rest. If the no-load reading fluctuates widely, changes randomly or reacts to every movement in the environment, there is no point in proceeding with calibration. You need to go back to the mechanics or the power supply, because code won’t ‘fix’ anything here. Only when the signal in the idle state is relatively stable can you start thinking about assigning a physical meaning to it.
Calibrating the HX711 – without it, are numbers just numbers?
The HX711 has no concept of a kilogram or a newton. From the system’s point of view, every reading is a dimensionless value resulting from a change in the input voltage. Calibration involves giving this number meaning by relating it to a known load.
The calibration process is always carried out using a real load, ideally one that you are familiar with and can consistently place on the sensor. A single load is usually sufficient, provided the mechanism is linear. Once the weight has been applied, you observe the difference between the zero and loaded states and use this to determine the scale factor.
It looks simple in the Arduino code, but it’s worth understanding what’s going on:
scale.tare(); // zerowanie układu
scale.set_scale(2280.0); // współczynnik kalibracji
and the figure isn’t ‘from the internet’ or ‘from a tutorial’. Every circuit has its own scale, determined by the strain gauge, the mechanics and the amplification. If you copy it from another project, you’ll get results that look good but are incorrect. It is good practice to perform the calibration several times and check whether the coefficient remains similar. If you get a completely different result each time, the problem lies further back in the measurement chain.
Averaging and filtering – peace of mind instead of confusing figures
The HX711 provides very detailed data. Sometimes a bit too much. A single reading is rarely of any practical use. Only a series of measurements allows you to draw meaningful conclusions. That is why averaging is not an option, but a necessity.
The simplest method is to take a few or a dozen or so samples and calculate the average. In practice, just 5–10 readings can significantly stabilise the result, provided that the mechanics do not introduce any vibrations.
Example of a reading with averaging:
float weight = scale.get_units(10);
Serial.println(weight, 2);
It’s not a perfect filter, but it’s sufficient for many projects. More importantly, averaging does not mask mechanical errors. If the structure flexes or vibrates, the average will fluctuate too. A digital filter is no substitute for a rigid base. In more demanding applications, additional software filters are used, but always as a supplement, not as a substitute for a poorly constructed system.
Drift and temperature – a problem that cannot be ‘coded’
One of the trickiest aspects of working with the HX711 is drift. The reading can change gradually over time, even without any change in load. This is most often caused by temperature, both of the strain gauge and the circuit itself.
Strain gauges change their properties as the temperature of the material changes. The HX711 detects and reports this. In amateur projects, this is usually ignored. In more sophisticated projects, one either recalibrates once a stable operating temperature has been reached or takes measurements under constant environmental conditions. If the project is intended to operate for a long time and remain stable, it is worth accepting the fact that the HX711 measures reality, and reality is not perfectly constant. Attempts to ‘freeze’ the reading in the code usually result in errors greater than the drift itself.
When does the HX711 Arduino work really well?
A well-designed system using the HX711 does not attract attention. The readings change only when the load actually changes. The system does not respond to random stimuli, and the figures are physically meaningful and consistent.
This is the result of combining several elements: sound mechanics, a stable power supply, correct calibration and simple, readable code. None of these elements is sufficient on its own. Only together do they form a measurement system, rather than merely a demonstration of the module’s operation. If, after a few days of testing, you stop checking the serial port monitor every minute, this is usually a sign that the HX711 is working as it should.
Summary
When used in conjunction with an Arduino, the HX711 can provide very good, stable measurements, but only if it is treated as part of a measurement system rather than a ready-made ‘black box’. The device does not tolerate mechanical errors, poor power supply or hasty calibration. Each of these factors has a direct impact on the result.
The most common problem lies not in the code, but in expectations. The HX711 shows reality as it is, with all its instability and imperfections. When the mechanics are rigid, the power supply is clean, and the calibration is carried out with care, the measurements stop ‘taking on a life of their own’ and begin to have real practical value.
If a project using the HX711 no longer requires constant monitoring and adjustments in the software, this is usually a sign that the circuit has been designed correctly. At that point, the Arduino ceases to be a toy and begins to serve as a useful measurement tool.
