Owners of budget smartphones often face a situation when during a conversation the screen goes out on its own or, conversely, the cheek presses the control buttons. On the Xiaomi Redmi 9A model, this issue is especially acute, since the design of the device has its own unique features of the location of the sensors. Understanding where the sensor is physically located and how it interacts with the system is the key to comfortable operation of the gadget.
Many users mistakenly assume that the sensor is hidden behind a dynamic grille or at the top of the case, which is not always true in this class of devices. In this article, we will discuss in detail the architecture of the proximity sensor, how to program it to verify and how to fix common errors, you will learn how to distinguish a software failure from a physical failure and whether to carry the phone into service.
The Redmi 9A features a virtual or software sensor, which is often confusing when looking for a physical hole on the front panel. The absence of a clear "eye" above the screen does not mean that the feature does not work - it is simply implemented differently than in flagship models.
Physical location and working principle
Unlike the more expensive Redmi models, which use a classic infrared sensor like a small black circle above the display, the 9A uses a Proximity Sensor technology based on the touchscreen and gyroscope algorithms. You won't find a physical window or hole on the front panel. The system analyzes the change in the screen capacity and the position of the phone in space to determine if you're held up to the ear.
This implementation allows the manufacturer to reduce the size of the frames and reduce the cost of production, but sometimes leads to less accurate work than infrared analogues. The sensor reads data that an object (your ear or cheek) covers a significant part of the upper zone of the display, which is why the use of dense protective glasses or cases with high sides can critically affect the correct operation.
⚠️ Attempts to find physical infrared port on Redmi front panel 9A Don't try to poke through the screen or disassemble the phone looking for a light bulb -- it's not there, and you'll only damage the matrix.
The principle of operation is based on a complex assessment of data. When you hold the phone to your head, the touch screen detects the absence of touches with your fingers in certain areas, and the accelerometer records the tilt of the device. If these conditions are met, the system blocks the display. The critical factor is the cleanliness of the top of the screen, since greasy spots can distort the sensor readings.
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Use only high-quality protective glass with cutouts for the speaker, so as not to create an additional obstacle to the operation of the sensor software algorithms.
Checking the performance through the engineering menu
To make sure that the proximity sensor on your Xiaomi Redmi 9A is functioning correctly, you need to use the built-in diagnostic tool CIT. This is a hidden part of the system that is accessible to all users without the need to obtain root rights.
The verification procedure shall be carried out as follows:
- 📞 Open the Phone app and enter the code ##6484## to log in to the menu. CIT.
- 📋 In the list that appears, look for the item "Proximity Sensor" or "Proximity Sensor" (usually at the beginning of the list).
- 👋 Hold your hand to the top of the screen for a distance. 2-3 See and remove it, watching the change in values.
- ✅ If the value changes from Far to Near, the hardware part is functional.
In the test, you'll see numerical values or textual statuses. If the screen stays black or the values don't change whether you put your hand up or not, it indicates a problem. It could be either software failure of the drivers or physical damage to the plume connecting the board to the display. In normal state, the reaction should be instantaneous.
☑️ Sensor diagnostics
Calibration of the sensor: step-by-step instructions
If the test shows that the sensor is working, but real calls are crashing (the screen is not going out or is not turning on), a forced calibration is required.This procedure resets the current sensitivity values and sets new reference points for Redmi 9A algorithms.
The calibration process looks like this:
- Go to the CIT engineering menu at ##6484##.
- Select the option "Proximity Sensor".
- Click the "Calibration" or "Start" button depending on the MIUI firmware version.
- Place the phone on a flat, horizontal surface (table) so that there are no objects above the screen.
- Press OK and wait until the process is complete. The phone can vibrate or make sounds.
Once successfully completed, the system will give a message "Pass" or "Success." It is important not to touch the device during calibration, otherwise the data will be recorded with an error. If the calibration did not pass the first time, repeat the procedure, making sure that the table surface is clean and smooth. In some cases, you need to restart the device to apply new parameters.
What to do if the calibration does not pass?
Configure through the Engineering Menu and ADB
For advanced users facing persistent problems, fine-tuning via USB debugging is possible.This method requires connecting the smartphone to the computer and having ADB drivers installed. It can change sensitivity thresholds that are not available in a conventional interface.
To access hidden settings, use the command:
adb shell am start -n com.android.engineeringmode/com.android.engineeringmode.EngineeringModeIn the menu that opens (if available on your version) MIUI) Or through specialized applications from the Play Market (for example, "Proximity Sensor Reset"), you can reset the configuration file of the sensor. ADB-commands allow you to restart the sensor service without a full reboot, which sometimes solves the problem of the hanging state of the "Near".
The table below shows the main statuses that you can meet with a deep diagnosis:
| Status | Description | Action. |
|---|---|---|
| Near (0) | Object found close by | The screen should go out. |
| Far (1) | There's no object nearby. | Screen active. |
| Null | No data from the sensor. | Calibration required |
| Error | Driver error | Fixing or repair |
⚠️ Note: Making changes through ADB-The commands can cause the system to be unstable. Write down any variables so you can get back the original values.
Effects of protective accessories and films
One of the most common causes of incorrect approach sensor on the Redmi 9A is the wrong accessories. Because the sensor in this model is software-based and tied to the capacity of the touchscreen, any thickening over the work area can be perceived by the system as a constant approach of the object, which leads to the screen going out immediately after the start of the call and does not respond to the distance of the phone.
Pay attention to the following factors:
- 🛡️ Glass thickness: glass that is too thick (more than 0.33 mm) can shield signals.
- 📱 High-sided covers: they can overlap the upper edge where the sensory areas are located.
- 💧 Mud and moisture: greasy spots at the top of the screen create "phantom" touches that knock calibration.
If you notice that the problem occurred after you stick a new glass, try to remove it carefully and check the sensor, which in most cases solves the problem instantly, and it is also recommended to regularly wipe the top of the screen with microfiber, especially before important calls to eliminate the impact of contamination on the capacitive layer.
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Removing the protective glass or replacing the case with a thinner one eliminates 80% of the problems with false sensor positives on the Redmi 9A.
Program conflicts and MIUI updates
Remember, it's not just hardware that controls the sensor, it's also software. The MIUI operating system on Redmi 9A gets updates that may be bugged in the sensor drivers. Sometimes, after a system update, users notice that the screen is behaving unpredictably, and in these cases, cleaning the cache or resetting the settings helps.
To avoid program conflicts, do the following:
- Go to Settings → Applications → All applications.
- Find the phone app (call).
- Select Memory and click Clear Cache (not data, exactly cache).
- Reset the device.
If the problem persists, there may be a conflict between some third-party application that has access to screen control or calls (e.g., number detectors, call recordings) and try to start the phone in Safe Mode and check the sensor, and if this mode is working correctly, then one of the apps you installed is to blame.