About replacing potentiometers in the gamepad

About replacing potentiometers in the gamepad

With the development of the gaming industry and its focus on consoles, gamepads are increasingly becoming standard input devices for PCs as well. In addition, game controllers can be used to control real-world objects, such as the infamous titan submarine. Thus, the question of repairing these controllers, including independent ones, often arises. And where there is a demand, there will be an offer. Online trading platforms are simply flooded with spare parts and parts for repairing gamepads.

The most frequent defect is the wear of potentiometers, which leads to jerky movements and maintenance of the zero, the so-called joint drift. Of course, the potentiometer can be cleaned, and the drift can be compensated with resistors, but this is a temporary measure, the resistive coating has already worn off, and the potentiometer itself needs to be replaced.

However, not all potentiometers are created equal. So, after installing this part, a huge “dead zone” appeared (an area near the neutral position in which the controller does not respond to the movement of the joint), and even a very sharp transition to the maximum or minimum value. That is, in fact, the stick ceases to be analog, but formally fulfills its function. Other potentiometers were purchased, in different colors, individually and as part of the 3d joint mechanisms, but they all behaved in a similar way. To find out what was wrong with these potentiometers, and how to fix it (spoiler – no way), a “measuring rig” was assembled and some “measurements” were made.

Photo of the installation and measured potentiometers.

The installation was assembled only once, and therefore it was made in the best DIY traditions – from boards and other materials at hand. The following are attached to the base: a crocodile clip for holding the measured potentiometer; and a servomotor designed to turn the potentiometer slider to a given angle. Such a design cannot guarantee the same setting of the potentiometers, but it is not necessary. The Raspberry Pi Pico board controls the servo motor and measures the voltage on the slider, the program is written in Micropython.

The measurement was carried out in the following way. The microcontroller successively changed the rotation angle from 30 to 150 (where 90 is the center or neutral position) by measuring the voltage from the potentiometer using the built-in ADC. After returning to 30° and repeating the process, and so 5 times. The turn was always made in one direction to avoid the effect of backlash.

The results of the measurements are presented in the figure.

Measurement results.

In the first three potentiometers, a characteristic step is visible in the 90° region, apparently this is metal spraying to ensure a dead zone. It can also be seen that the range with resistive sputtering is only 10°. The last two graphs show the results for “good” potentiometers, the voltage value is proportional to the angle of rotation over a wide range and without steps.

In the fourth graph, the measurement results of the original ALPS potentiometer from the dualshock 4 (the data is slightly blurred because I held it with my hand), and in the fifth graph, the new one bought together with the 3d mechanism, and it was bought from the same online store ( not China ), same as the orange potentiometer in the second graph.

Initially, this “research” was conducted to somehow linearize the characteristic of “bad” potentiometers. However, as can be seen from the graphs, this is impossible.

Conclusion: At the moment, it is impossible to determine what type of potentiometer is sold in the store. The main problem is to sneeze at everyone. Occasionally you can find feedback like “Replaced, dead zones appeared, but generally normal.”

Related posts