TECHNICAL SUPPORT
Published 2026-03-25
Many friends get the SG90servofor the first time. Faced with three wires and a bunch of parameters, they are often confused: How does this thing turn? Do I need to buy a special driver board? Don't worry, today we will break down the SG90servodrive circuit schematic diagram so that you not only know how to wire it, but also understand the logic behind it.
The SG90 servo leads to three wires, usually in brown, red, and orange colors. The brown wire is the ground wire, which is connected to the negative pole of the power supply or the GND of the development board; the red wire is the positive pole of the power supply, which needs to be connected to a power supply of about 5V; the orange wire is the signal wire, which is responsible for receiving control pulses. ️ Here comes the key point: the signal line must be connected to the PWM output pin of the microcontroller (for example). Many novices will connect the power supply and signal wires in reverse, causing the servo to not work or even burn down, so be sure to confirm the color correspondence before wiring.
In actual projects, if you are using it, you can directly draw power from the 5V pin on the board, but note that the current may exceed 0.5A when the SG90 is blocked. If multiple servos are driven at the same time, it is best to use a separate 5V power module for power supply. Connect the power and ground wires of the servo to the ground wire of the control board, and connect the signal wires to the corresponding pins, and a complete prototype of the drive circuit is ready.
The SG90 servo is driven by a special pulse signal, which is PWM (Pulse Width Modulation). To put it simply, you don't need to give it the instruction "how much to turn", but tell it where to stop by changing the width of the pulse. The standard control period is 20ms. During this period, the pulse width varies between 0.5ms and 2.5ms, corresponding to angles from 0° to 180° respectively.
For example, if you want the servo to turn to the middle 90° position, output a high level for 1.5ms and keep it low for the remaining time, repeating every 20ms. Many friends who are just getting started tend to confuse PWM duty cycle and frequency. In fact, for SG90, you only need to pay attention to "how long the high level lasts". This control method is very intuitive. As long as your microcontroller supports PWM output, or you use an ordinary IO port to simulate PWM, you can easily achieve angle positioning.
Power supply is the most problematic link in the drive circuit. The rated operating voltage of SG90 is 4.8V to 6.0V, usually we use 5V for power supply. But please note that when the servo is started or suddenly changes direction, the instantaneous current will surge to 0.5A or even higher. If you directly use the 5V pin on the microcontroller development board to power the servo, it may cause a voltage drop, causing the microcontroller to reset, or the servo to vibrate or not rotate.
The solution to this problem is simple: use an external power supply. For example, use two lithium batteries in series (7.4V) and add a 5V voltage stabilizing module, or directly use a 18650 lithium battery with a boost module to ensure that the power supply can provide a continuous current of more than 1A. At the same time, be sure to connect the ground wire of the external power supply to the ground wire of the microcontroller to form a common ground so that signals can be transmitted normally. Stable power supply is the basis for reliable operation of the steering gear, and this step cannot be sloppy.
How to confirm that there is no problem after the circuit is connected? We recommend the simplest test method: first use a program to make the servo automatically swing back and forth in three positions: 0°, 90°, and 180°. You can use the Servo library and you can do it with just a few lines of code. If the servo can swing smoothly and there is no abnormal sound, it means that the drive circuit is basically normal.
If the servo does not turn, check in this order: first, use a multimeter to check whether the voltage between the red line and the brown line is about 5V; then check whether the signal line is soldered; finally, use an oscilloscope or logic analyzer to see if the PWM signal waveform is correct. Many beginners suspect that the servo is broken when they first start. In fact, most problems lie in the power supply or loose wiring. Through this step-by-step testing, you can quickly locate the problem and accumulate debugging experience.
In actual use, you may encounter servo vibration, severe heating, or inaccurate steering. Jitter is usually caused by insufficient power supply or interference with the PWM signal. In this case, an electrolytic capacitor of more than 100uF can be connected in parallel near the power pin to play a filtering role. If the heat is severe, the mechanical load may be too heavy or the steering gear may be blocked for a long time. You need to check whether the transmission mechanism is smooth.
There is also a situation where the servo can only turn in one direction. This is often because the minimum or maximum width of the PWM pulse is not set correctly, causing the control range to shift. It is recommended to fine-tune the upper and lower limits of the pulse width in the code, such as changing the pulse width corresponding to 0° from 0.5ms to 0.6ms, and slowly find the most appropriate parameters. You will basically encounter these fault phenomena. Treat them as the "only way" in the debugging process. Solve them once and the rest will be much smoother.
After you run through the driver circuit, you can use it in actual projects. For example, you can make a simple robotic arm and use a few SG90s with a servo bracket to achieve grabbing actions; or you can install it on a gimbal and use it with a camera for target tracking; you can even use it to control steering on a smart car. The key is to consider modularity when designing the circuit: make the steering gear power supply and control signal interface into standard connectors to facilitate later replacement or expansion.
If you want to make more complex products, such as multi-degree-of-freedom robots, you have to use a specialized servo control board. These control boards usually come with their own voltage stabilizing circuits and interfaces, which can drive 16 or even 32 servos at the same time, and receive instructions through the serial port, which greatly simplifies the design of the drive circuit. No matter which solution you choose, as long as you master the driving principle of SG90, you can flexibly integrate it into your own creativity and let your ideas really move.
In what scenario do you plan to use your first SG90 servo project? You are welcome to leave a message in the comment area to chat about your creativity. You can also write down the problems encountered during debugging, and we will discuss and solve them together. If this article helped you understand the driving circuit, don’t forget to like it so that more friends in need can see it~
Update Time：2026-03-25
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