The Microcontroller Can't Drive The Servo? Teach You A Trick To Solve The Problem Of Power Shortage

Hey friends! When working on a robot or smart car project, have you ever encountered this annoying thing: Although the program is written correctly, theservoseems to have not eaten, shaking after a few times and then stopping, or simply not moving at all? This situation of "the microcontroller cannot drive theservo" will happen to almost every novice who plays theservo. Don't worry, it's usually not that your code is wrong, but that there's something wrong with the power supply or the driving method. Today we are going to talk about how to solve this annoying problem and make your servo "strength" again.

Why does the servo go down as soon as it is powered on?

Many friends plug the power cord of the servo directly into the 5V pin of the microcontroller as soon as they get started, thinking this is the most convenient. But you know what? When an ordinary servo is working, the current demand may reach several hundred milliamps or even higher, while the 5V output pin on the microcontroller can usually only provide tens to one or two hundred milliamps of current. This is like asking a small water pipe to drive a large water pump, which instantly lowers the water pressure, causing the voltage of the microcontroller to become unstable, directly resetting or the program runs away, and the servo naturally cannot move.

Another situation is that you use a battery to power the entire system, but the battery voltage is sharply pulled down the moment the servo is started. Imagine that when the air conditioner in your home is turned on, the light bulbs dim. The principle is the same. If this voltage drop exceeds the working range of the microcontroller and steering gear, the system will strike. Therefore, insufficient power supply is the number one culprit of the steering gear "slumping".

How to provide separate power supply to the servo?

Now that we know that "power grabbing" is causing the trouble, the most direct way is to provide a "canteen" for the servo and the microcontroller and eat separately. The control circuit of the microcontroller and the power circuit of the steering gear should use two independent power supplies. For example, the microcontroller is powered by USB or a low-power 5V power supply, while the servo is directly powered by a set of high-current battery packs (such as 4-cell nickel-metal hydride batteries or 2 strings of lithium batteries).

The benefit of this is particularly obvious. When the servo rotates vigorously, its current impact will only affect its own power supply. The power supply of the microcontroller is as stable as a mountain, and the program can run stably. You only need to pay attention to connecting the ground wires (GND) of the two power supplies together so that the control signals of the microcontroller have a common voltage reference point and can be successfully transmitted to the servo. Remember, only connect the ground wire. Never connect the positive terminals of the two power supplies together.

Is it necessary to add a servo drive board?

If you only use a small servo in your project, and your microcontroller power supply does have margin, you may not need to add it. But in most cases, especially when using high-torque servos or using several servos at the same time, it is strongly recommended to add a servo drive board. This is not an unnecessary step, but an "insurance" for your system.

The servo drive board (such as this type of module) itself has a high-current power interface, which can be directly connected to the battery to power the servo. More importantly, it isolates the weak current control on the microcontroller side from the strong current drive on the steering gear side through components such as optocouplers. In this way, no matter how large the current fluctuations at the servo are, your expensive microcontroller main control board will not be burned, which is safe and worry-free.

How to choose the right power supply

There are two main parameters when choosing a power supply: voltage and current. The voltage must strictly match your servo specifications. For example, the commonly used SG90 servo is 5V, and the servo can be 6V-7.2V. The current needs to be calculated by adding up the maximum current of all servos when they are blocked, and then multiplying by a safety factor (such as 1.5 times). For example, if a servo has a locked-rotor current of 1A and you use four, the power supply must be able to stably output at least 6A.

Don't try to buy a low-quality power supply with an artificially high nominal current at a low price. A stable power supply with small output voltage fluctuations can ensure consistent torque output of the servo and more accurate movements. In addition, remember to connect a large-capacity electrolytic capacitor (such as 1000 microfarads) in parallel between the positive and negative terminals of the servo power supply. This is like a small reservoir, which can effectively absorb instantaneous current shocks and is very helpful for stabilizing the voltage.

How to avoid lag in the program

Now that the hardware is done, the software needs to be coordinated. Some friends like to let the servo rotate to different angles quickly and continuously in the program without any delay. This will make the servo control signals too dense, the microcontroller will be busy sending pulses, and the mechanical structure of the servo itself will not respond so quickly, which will easily cause "choking", which manifests as jitter or stuck movements.

The solution is very simple. After each change of the servo angle, add a small appropriate delay (such as 10-20 milliseconds) to allow sufficient response time for the servo. If you are using multiple servos, the control signals should be evenly distributed. Don't squeeze the control instructions of several servos at the same time. If you stagger the time a little, the action will be much smoother.

How to check if there is a program logic problem

Sometimes the problem is not the hardware, but the logic "fighting" in your code. For example, there is a long delay in your main loop, or a task that takes a long time to complete (such as waiting for a sensor to trigger). During this period of time, the microcontroller has no time to process the continuous pulse signals required by the servo, and the servo will lose power and start to vibrate because it cannot receive the signal.

At this point, you need to check the code structure. Try not to use a dead-end function likedelay()in the main loop. Instead, use a timer interrupt to generate the servo control signal, or put the servo pulse generation in the interrupt. In this way, no matter what the main program is doing, the interrupt will generate pulses on time, and the servo can maintain its position steadily without losing the chain.

Friends, after reading these points, do you feel that the problem of "the microcontroller cannot drive the servo" is no longer so mysterious? Think back to the situation you encountered. Is it mainly a power supply problem, a driver problem, or a code logic problem? Welcome to leave a message in the comment area and tell us where your project is stuck. Let's communicate together. By the way, give it a like and share it with more friends who are "scratching their heads"!