The Xiaomi Mi A3, part of the Android One program, comes with a standard set of sensors needed for comfortable operation, but their physical location often raises questions among users. The proximity sensor is a tiny but critical element that locks the screen during a conversation, preventing accidental cheekstrokes. Understanding where it is located helps not only in household use, but also in diagnosing malfunctions or sticking protective glasses.
Unlike many budget models, where the sensor is often hidden in a narrow strip above the display, the Mi A3 engineers have taken a more modern solution by hiding it under the screen panel. This makes the device more visually attractive, but makes it difficult to visually identify the component. If you are faced with a situation where the screen goes out on its own or, conversely, does not respond to the application to the ear, knowing the architecture of the device is the first step to solving the problem.
Next, we'll go into detail about the design of the front panel, the methods of software verification and the methods of manual calibration that will return the correct operation of the sensor. It is important to understand that software failures are more common than physical failure, so before you carry the phone to the service, you should try to fix the situation yourself.
Design features of the front panel Mi A3
The front of the Xiaomi Mi A3 is made using In-Display Fingerprint technology, which implies that there is no visible frame for the fingerprint scanner, but the proximity sensor here is also hidden from the user's eyes. It is integrated directly into the display module or placed in a minimum gap between the screen and the body, which is typical for devices with a drop-like cutout. Visually, you will not see a separate window or a black circle, since the sensor works through the protective glass of the matrix.
This arrangement requires high-precision assembly and high-quality protective films. If you use a cheap protective glass with an opaque frame or offset holes, this can cause incorrect operation. The light emitted by the sensor can reflect from the inner surfaces of the poor accessory, creating a false sense of proximity of the object.
⚠️ Warning: The use of protective glasses with a wide black frame that covers the top of the display is the most common cause of false sensor alarms on models with a hidden sensor.
The physical location of the element is driven by the need to minimize the front panel. In the Mi A3, the main communication modules, including the speaker for conversation and the front camera, are also grouped at the top. The sensor is usually in close proximity to the conversational speaker, which is hidden under a thin slit in the body.
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When buying a protective glass for Xiaomi Mi A3, choose options marked "Full Coverage" or specially designed for this model to avoid overlapping the sensors.
The principle of operation of the infrared sensor
To understand the causes of possible failures, you need to know exactly how this component works. The proximity sensor in the Xiaomi Mi A3 works on the infrared principle: it emits an invisible beam and analyzes its reflection from nearby objects. If the reflected signal returns quickly and with sufficient intensity, the system is instructed to turn off the backlight and touchscreen.
This process occurs continuously during active voice calls. Calibration is the process of adjusting the sensitivity to ignore background interference but respond to the phone being brought to the head. A software failure can cause the threshold to be knocked down and the phone to "think" it's in the ear all the time.
Importantly, external factors such as bright sun or total darkness can affect the sensor, although algorithms have taken this into account in current models, but physical obstacles such as dust at the top of the dynamic hole or greasy spots can distort readings.
- 📡 The sensor emits infrared light that is not visible to the human eye but can be captured by another phone’s camera.
- 📏 The response distance is usually 1 to 5 centimeters, which is optimal for a conversation scenario.
- ⚙️ The software driver constantly polls the state of the sensor at a high frequency to instantly respond to changes.
Diagnostics of malfunctions through the engineering menu
The most reliable way to test the operability of the proximity sensor on the Xiaomi Mi A3 is to use the built-in engineering test menu, which allows you to see raw data from the sensor in real time, which eliminates guesswork. It does not require superuser rights to access it, just enter a special code in the Phone application.
In the menu that opens, you need to select the item that is responsible for checking components. Often it is designated as Proximity Sensor or has the corresponding icon. When you press the check button, the screen can go out, and you will need to close the sensor with your finger to see the response of the system. Digital values will vary from 0.0 (object not) to 5.0 (object nearby).
##6484##If the values do not change when you bring your hand to the top of the screen, this may indicate a software driver failure or physical damage to the plume. In some cases, a simple reboot of the device helps, which resets temporary errors in the memory of the controller.
☑️ Sensor diagnostics
Manual sensor calibration procedure
If the diagnostics show that the sensor is responding but is not doing it correctly (for example, it is turning off the screen too soon or too late), calibration is necessary. In smartphones of the Mi A line and many other devices on pure Android, this procedure can be hidden from the average user, but is available through special applications or hidden settings menus.
To calibrate, the phone must lie on a perfectly flat horizontal surface, which is critical because the system reads the "baseline" distance to the object (table) as zero, and if the phone is tilted, the calibration will go wrong, and the screen can behave unpredictably in the future.
As you calibrate, the system will ask you to remove your hand from the screen several times and then close the sensor, and you need to do this clearly and quickly, and once you've finished the procedure, the phone will automatically reboot or return to the menu, saving the new sensitivity factors to non-volatile memory.
| Calibration phase | User action | Expected output |
|---|---|---|
| 1. Preparation | Put your phone on a flat surface | The screen is on, nothing disturbs. |
| 2.Dumping | Press the "Start" or "Calibrate" button. | Starting the measurement process |
| 3. Closing | Close the top of the screen with your palm | The screen goes out, the data is being recorded. |
| Completion | Remove your hand and wait until it's over. | Message "Success" or reboot |
⚠️ Warning: Don't calibrate with your phone in your hands, only a solid horizontal surface guarantees correct measurements of infinity".
What if calibration doesn’t help?
Program conflicts and third-party applications
Sometimes the problem isn't hardware, it's software. Android One on the Mi A3 is pretty clean, but application conflicts can disrupt system sensors, especially after you upgrade or install apps that monitor calls and record conversations.
Call recording applications, smart numbering calls and launchers can intercept the sensor. If the application contains an error, it may not give control back to the system, blocking it in an active state.
It is also worth checking for updates to the Phone app itself through the Google Play Store. Google regularly releases patches that fix compatibility bugs with specific hardware models. The cache of the telephony app is also worth cleaning, as accumulated temporary files can cause malfunctions in the logic of the work.
- 📱 Remove newly installed apps that have access to microphones and sensors.
- 🔄 Update the Google Phone app to the latest version via the Play Store.
- 🧹 Clear the cache and data of the "Phone" application in the system settings.
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In most cases (about 80%) the problem is solved by software calibration or removal of poor-quality protective glass that does not require physical intervention.
Physical damage and repair
If software methods fail, a physical malfunction is likely. In the Xiaomi Mi A3, the proximity sensor is often integrated into a flexible plume that connects the lower charging board to the main motherboard, or is part of the display module.
Moisture is another common risk factor, and even if the phone hasn't sunk, high humidity or raindrops can oxidize the contacts in the upper speaker area, and visual inspection through the magnifier can sometimes reveal traces of corrosion or dirt clogging the speaker's opening.
Self-replacement of the sensor requires skills with small electronics and the availability of tools: a dryer for heating glue, suckers, a set of screwdrivers and mediators. Given the design of the Mi A3 with a fingerprint scanner in the screen, careless disassembly can lead to damage to the display, so if you do not have experience, it is better to contact the service.
At the service center, the technicians will do a multimeter diagnostic, check the voltage on the sensor contacts, and if the circuit rings but the sensor doesn't work, the module is replaced, and the cost of this repair is usually lower than replacing the entire screen if you can find a compatible plume separately.