{"id":9888,"date":"2022-03-01T22:41:44","date_gmt":"2022-03-01T22:41:44","guid":{"rendered":"https:\/\/liquidinstruments.com\/?p=9888"},"modified":"2025-12-11T22:34:56","modified_gmt":"2025-12-11T22:34:56","slug":"closed-loop-tuning-with-mokugos-pid-controller","status":"publish","type":"post","link":"https:\/\/liquidinstruments.com\/application-notes\/closed-loop-tuning-with-mokugos-pid-controller\/","title":{"rendered":"Closed-loop tuning lab using the Moku:Go PID Controller","gt_translate_keys":[{"key":"rendered","format":"text"}]},"content":{"rendered":"

Moku:Go<\/h2>\n

\"Moku:Go<\/p>\n

Moku:Go combines 15+ lab instruments in one high-performance device. This application note uses the Moku:Go PID Controller, Oscilloscope, and Programmable Power Supplies to provide a visually engaging way of learning various tuning methods for PID controllers.<\/p>\n

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\"UT<\/p>\n

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Introduction<\/h2>\n

The Proportional-Integral-Derivative (PID) controller is one of the most common forms of feedback control, and  is used in a wide variety of applications like the cruise control in your car or motor control in a drone. The purpose of a PID controller is to drive a process to reach a specified output, typically called a setpoint. The feedback of the controller is used to regulate and optimize the control of this process. Moku:Go features a digitally-controlled PID Controller. The graphical user interface dynamically visualizes the gain profiles, giving the user the ability to drag and drop gain values directly onto a frequency response graph which calculates and displays the transfer function of the PID controller in real time. This allows the student to directly see the poles and zeros of the system as they vary the PID gain values and crossover frequencies.<\/p>\n

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The purpose of this application is to demonstrate how control theory labs can be updated to better suit the needs of modern undergraduate labs. Typically, control theory is taught through rigorous mathematical modeling with few, if any, physical labs that utilize equipment. This application introduces a modern approach to control theory education by applying a more visual component that helps students more readily connect the theory learned in the classroom to real-life control systems. This is done by controlling the height of a ping-pong ball by using a DC motor fan, an IR distance sensor, and several of the integrated instruments available for Moku:Go. Moku:Go offers 15+ lab instruments, three of which are used for this experiment: the Oscilloscope, PID Controller, and Programmable Power Supplies. Most of these instruments are used simultaneously and can drive the motor control circuitry, take in sensor data, and output a specified signal to control the DC motor\u2019s speed simultaneously. This way, characteristics like the rise time, overshoot, and steady-state height of the ping-pong ball can be controlled and measured from a universal graphical user interface, enabling students to grasp multiple advanced concepts quickly. It also allows real-time tuning through the Moku: app so that students can see how the different PID gains impact the system both mathematically and physically.<\/p>\n

Theory of Operation<\/h2>\n

One Moku:Go will be used in this experiment to power the PCB, read sensor data, implement a PID controller, and generate a control signal. The Moku:Go M2 model has a four-channel programmable power supply unit (PPSU) that is very useful in projects like this and allows it to be a one-box solution for many labs. Two PPSU channels are used in this experiment to power the PCB and the DC fan which is the primary system to be controlled. Moku:Go also has two input channels for reading data and two output channels for generating waveforms. In this experiment, both input channels and one output channel are being used for reading data and generating a control signal. See the figure below for how the PID Demo kit and Moku:Go operate together in a closed-loop system.<\/p>\n

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Figure 1: PID demo kit block diagram<\/em><\/p>\n

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\"Figure<\/p>\n

Figure 2: Moku:Go PID controller with demo kit block diagram<\/em><\/p>\n

ADC1 will read the setpoint signal which is controlled by a potentiometer. ADC2 will read the IR sensor which is affixed to the top of the tube. These two signals are sent to the PID controller running on Moku:Go while the control signal is generated by the DAC and sent to the PWM driver circuit. This control signal will determine the PWM\u2019s duty cycle, which will directly alter the DC fan and, subsequently, the ball\u2019s height inside the tube.<\/p>\n

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The PWM driver operates by using the NE555 timer (U1) to generate a sawtooth waveform which is fed into the inverting input of the comparator (U2). The PID controller\u2019s output from the Moku:Go (Out1 or DAC1) is fed into the non-inverting input of the comparator, which generates a PWM signal. This signal is sent to a MOSFET (Q2) that controls the power consumed by the 5 V fan. The amount of power the fan sees directly translates to the height that the ping-pong ball will levitate.<\/p>\n

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Figure 3: PID controller demo schematic<\/em><\/p>\n

The other part of this lab setup is the mechanical system used to levitate the ball. It consists of a 5 V DC fan, 3D printed parts (tube, fan connector, and sensor connector), an IR sensor, and a ping-pong ball. The tube has a \u00bc inch width slit in the side that acts as variable resistance to the system. There are smaller perpendicular slits marking every 20 mm. The markings should be used to measure from the top of the ball, because this is what the IR sensor sees first. This is important for tuning the PID controller later.<\/p>\n

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Experimental Setup<\/h2>\n

Components List<\/h4>\n