TECHNICAL SUPPORT
Published 2026-03-19
You must have thought about this: The 51 microcontroller is so classic and cheap, can it be used to control theservo? The answer is yes, and in more ways than one. Today we will talk about how to use the 51 microcontroller to play theservoand make your small craft move.
The steering gear is actually a "lazy guy". As long as you tell it where to turn, it will use its internal circuits and motors to run to that position. The way to tell it is a PWM wave, which is a square wave signal with adjustable width. A standardservorequires a pulse cycle of 20 milliseconds, where the width of the high level determines the angle of the servo.
Although the 51 microcontroller does not have a dedicated hardware PWM module (the old model does not have it, and we will talk about the enhanced version separately), we can use a timer to simulate it. It's like using a stopwatch to measure time, letting a pin output a high level first, then pull it low when the timer expires, and wait until the 20 millisecond period ends before repeating. As long as the timing is accurate enough, the 51 microcontroller is fully capable of this task.
To make the servo rotate, a microcontroller alone is not enough. First of all, you need to have a servo, such as the low-power SG90, which is easy to use. Then there is the power supply, which is particularly important. The working current of the servo is not small, especially at the moment of startup. Taking power directly from the microcontroller development board can easily cause the microcontroller to restart. Therefore, you need to prepare a separate 5V power supply for the servo, such as a battery pack or voltage stabilizing module.
Other small components are also indispensable: a breadboard or DuPont wire is used for connection. It is best to prepare a capacitor of about 100 microfarads and filter it at both ends of the servo power supply. The capacitor can act like a small reservoir, buffering current fluctuations, making the steering gear work more stable, and preventing the microcontroller from being "implicated" in reset.
The core idea of writing a program is to use a timer to generate a 20 millisecond period and control the pin to output pulses of different widths during the period. For example, we set the timer to interrupt every 0.1 milliseconds and then count. If you want to output a pulse of 1.5 milliseconds, pull the pin low when the count reaches 15 in the interrupt, and then pull the pin high when the count reaches 200 (20 milliseconds arrives), and so on.
The code is not complicated to write either. In the timer interrupt service function, use the if statement to determine whether the current count value reaches the set pulse width value, and then clear the servo pin to zero. In the main program, you only need to modify the variable corresponding to the pulse width value to easily change the steering gear angle. Of course, don't forget to initialize the timer and interrupt, which are the basis for the program to run.
The rotation angle of the steering gear is directly determined by the high-level pulse width, and the relationship between the two is basically linear. Generally speaking, a pulse of 0.5 milliseconds corresponds to 0 degrees, 1.5 milliseconds corresponds to 90 degrees, and 2.5 milliseconds corresponds to 180 degrees. Different brands of servos may have slight differences, but this is the general range.
So how do you set the angle in the program? We can define an angle variable and then use a simple formula to calculate the required pulse width: pulse width = 0.5 + (angle/180)*2.0, the unit is milliseconds. Then convert this time into a timer count value. For example, if there is one interrupt in 0.1 milliseconds as mentioned before, then 1.5 milliseconds is 15 interrupts. Finally, just assign this count value to the comparison variable in the interrupt. Simple, right?
There is often more than one steering gear in a project. For example, making a six-legged robot requires many. A common method for using a 51 microcontroller to control multiple servos is "time-sharing multiplexing". Since each servo requires a 20 millisecond period pulse, we can divide 20 milliseconds into several segments, and each segment outputs a servo pulse. For example, first send a pulse of 0.5 to 2.5 milliseconds to servo No. 1, and then immediately send a pulse to servo No. 2, and so on, as long as the pulses of all servos are sent within 20 milliseconds.
This method requires multiple IO ports, and the interrupt program must be arranged in order. If your microcontroller is an enhanced microcontroller with a hardware PWM module, it will be more worry-free. You can directly configure multiple PWM outputs, the CPU hardly needs to worry about it, and the accuracy is higher. For novices, practice using time-sharing multiplexing first, and then consider upgrading methods after understanding the principles.
The most common thing encountered when playing with servos is jitter. This is usually a power supply problem. When the servo moves, the voltage is pulled down, and the microcontroller is not working properly, causing signal disorder. The solution is to strengthen the power supply, use an independent power supply, and make the power and ground wires as thick and short as possible, and the capacitor should be installed close to the servo.
Sometimes the servo angle is incorrect or the response is slow. This may be due to interference on the signal line, or the timing in the program is not accurate enough. You can connect a 10k pull-down resistor to the signal line to ground to improve the anti-interference ability. In terms of program, check whether the crystal oscillator is accurate and whether the initial value of the timer is calculated incorrectly. Make sure these foundations are OK, and your servo will be able to hit where you want it.
In the process of using the 51 microcontroller to play with the servo, have you encountered any particularly interesting faults or come up with any interesting applications? Welcome to leave a message and share in the comment area, and don’t forget to like and save it so that more friends can see these practical tips!
Update Time：2026-03-19
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