
Abstract—This paper presents a personal computer (PC)-based data acquisition and control
(DAC) tool that is incarnated by using a Peripheral Interface Controller (PIC) microcontroller,
Matlab, and Simulink. We exploit the serial communication capability of both the PIC microcontroller and Matlab to merge these technologies and to provide an inexpensive DAC solution. Angular position control of a DC motor is demonstrated to show efficacy of the PCbased data acquisition and control tool using PIC microcontrollers, Matlab, and Simulink.
I.
INTRODUCTION
A data acquisition and control (DAC) tool is broadly used for communication between sensors/actuators and decision making devices such as a personal computer (PC). For this reason, data acquisition and control (DAC) systems are required in various fields such as instrumentation and control systems. Many DAC systems that target the educational sector are currently widely available. Current DAC systems, however, tend to be quite expensive. Furthermore, academic labs generally do not require the intrinsic high performance features of these DAC systems (e.g., high sampling rates, high resolution analog to digital converters, etc.) to educate students. Our proposed DAC system is particularly beneficial to educators interested in building inexpensive experiments that are capable of utilizing the Matlab and Simulink icon-based programming environment for data acquisition and control, while not requiring the aforementioned stringent hardware requirements.
In the previous developments of making DAC systems manageably inexpensive, Lee et al.
[1] and Li et al.
[2]
developed Matlab-based graphical user interface (GUI) using a Peripheral
Interface Controller (PIC) microcontroller and a Basic Stamp 2 (BS2) microcontroller respectively. Nevertheless in those projects users have to know PIC assembly programming language for PIC microcontrollers and PBasic programming language for the BS2 microcontroller to program the microcontrollers for the Matlab-based DAC systems. Those programming languages are not widespread programming languages such as C or Java, which means that users have to spend extra time to learn those programming languages to construct the
DAC systems developed in the two aforementioned papers. Panda et al.
[3]
solved the problem by developing a Matlab data acquisition and control toolbox using a BS2 microcontroller. With this development, users no longer need to have prior knowledge of the PBasic programming language to program a BS2 microcontroller to develop the Matlab-based GUI. The predefined BS2 Library of the Matlab and Simulink takes the part of generating and programming proper PBasic codes for BS2 microcontroller. The BS2 microcontroller, however, requires external devices to make smooth connection between the BS2 DAC system and PC such as an analog to digital converter
(ADC). Fortunately some PIC microcontrollers already have built-in ADC functionality, which

BS2 microcontrollers don’t. In this paper, we develop a low-cost PC-based DAC board using a
Microchip Co.
[4] ’s PIC microcontroller.
The method for a Matlab DAC toolbox using a BS2 microcontroller [3] is exploited to develop a Matlab-based DAC toolbox for PIC microcontrollers. Therefore users are not required to have prior knowledge of PIC assembly programming language. Users rather simply use a predefined
PIC library, which exploits Simulink’s icon-based programming environment to implement userdefined algorithms in a block diagram format in this Matlab-based DAC toolbox. In particular, our software environment allows i) the generation of proper PIC assembly codes for a variety of sensors and actuators, ii) programming of the PIC microcontroller, and iii) data communication between the PIC microcontroller and Matlab. In addition, the advantage of built-in analog to digital converters from a PIC microcontroller is utilized. We also build upon the foundation of a previously developed Matlab-based GUI using a PIC microcontroller
[1]
to exploit Simulink and
Matlab’s built-in serial communication capabilities to communicate with various sensors and actuators connected to a PIC microcontroller.
In this development, we use a PIC16F74, 40-pin, 8-bit Complementary Metal-Oxide
Semiconductor (CMOS) Fast Low-Latency Access with Seamless Handoff (FLASH) dual inline package IC. The proposed environment is particularly beneficial to educators interested in building systems that use basic controls with minimal hardware costs.
This paper is organized as follows. First, in Section II, we describe the PIC microcontroller and development hardware. Next, in Section III, we describe our software interface in detail. In
Section IV, we provide details on the software integration of Simulink with the PIC microcontroller. In Section V, we illustrate the functionality of our proposed DAC system by performing position control of a DC motor. Finally, in Section VI, we draw some concluding remarks.
II.
H
ARWARE
E
NVIRONMENT
The hardware environment required for this DAC system consists of a PIC microcontroller, a
PC, a PIC-PG2C programmer, a PIC development board, a RS232 driver/receiver, and a DB-9 serial cable. The PIC microcontroller is interfaced with external devices such as sensors (e.g., potentiometers, photoresistors) and actuators (e.g., LEDs, DC motors). The PC hosts the interactive DAC Toolbox for the user to manipulate control variables and visualize sensory data.
The PIC microcontroller and the PC communicate with each other using a serial interface. The
PIC development board (see section II—F) and a DC motor experiment test bed (see section V) are used to illustrate our PIC-based DAC approach.

Figure 1: Hardwares
A.
Peripheral Interface Controller
PIC microcontrollers, manufactured by Microchip, Inc., are small, low-cost controllers that include a processor and a variety of peripherals. PIC microcontrollers are significantly easier to use vis-à-vis embedded microprocessors. As an example, users can assign desired functionality
(e.g., ADC, USART
1
) to I/O pins of PIC microcontrollers. PIC microcontrollers can be operated at various clock speeds (32 kHz to 20 MHz). PIC microcontrollers’ memory architecture separates its data memory from its program memory with the program memory available as One-
Time Programmable (OTP), Erasable Programmable Read-Only Memory (EPROM), or FLASH.
PIC microcontrollers are programmed in the PIC assembly language using a 35 single-word instruction set. See
[4]
for more details on hardware and software features of PIC microcontrollers.
The user specified embedded PIC program in the Matlab-based DAC toolbox is written on the
PC and downloaded from the PC to the PIC microcontroller using the DB-9 serial cable connection between the PC and the PIC Development Programmer on which the PIC microcontroller is mounted. Commonly available PIC Development Programmers include
PICSTART Plus from Microchip, Inc. and PIC-PG2C from Olimex, Ltd.
[5]
. The PIC-PG2C is a handy and low-cost programmer. In this project, we use the PIC-PG2C programmer that requires
ICPROG, free software available on the website [6] , for programming PIC microcontrollers.
In this paper, we employ a PIC16F74, a 40-pin CMOS FLASH-based, 8-bit, mid-range (14-bit instruction word length) microcontroller. The PIC16F74 has 4 Kbytes of FLASH program memory and 192 bytes of data memory. Furthermore, it has 33 digital I/O pins organized in 5 groups of I/O ports that can be assigned as 8-bit ADCs, Capture/Compare/PWMs
2
(CCPs), the 3wire Serial Peripheral Interfaces (SPIs), the 2-wire Inter-Integrated Circuit (I
2
C) buses, USART ports, etc. In this project, one set of I/O port is assigned for 8 channel 8-bit ADCs and another set of ports is assigned for 8 channel outputs. We use an external 20 MHz high-speed crystal oscillator to supply operating clock cycles. The PIC16F74 can be powered using a wide range of voltage sources, e.g., 2-volt direct current (VDC) to 5.5VDC, and each of its I/O pins can sink or source up to 25mA of current. It is ideal for not only laboratory data acquisition (the application
1 Universal synchronous/asynchronous receiver and transmitter.
2 Pulse width modulation.

considered in this paper), but also automotive, industrial, and consumer applications.
B.
PIC-PG2C Programmer
PIC-PG2C programmer (see Figure 2) is a PIC microcontroller programmer manufactured by
Olimex, Ltd. The programmer is used to download PIC HEX code, converted from PIC assembly code, into a PIC microcontroller via a serial cable. Different from other PIC programmers, it doesn’t require any additional power supply for itself. Instead it is supplied with not only all necessary signals but also power from a serial port on a PC. So it may not work properly if a laptop computer is used because of power shortage from the laptop computer.
(a) (b)
Figure 2: (a) PIC-PG2C programmer and a PIC, (b) PIC-PG2C programmer with a PIC mounted
C.
RS232Driver/Receiver
MAX232 is a 2-channel, RS232 driver and receiver manufactured by Maxim Integrated
Products, Inc
[7]
. It requires a 5VDC power supply and converts voltage levels between PC-based logic and PIC microcontroller-based logic. Specifically, the voltage levels of logic high and logic low for PIC microcontrollers, like many other microcontrollers, correspond to 5VDC and 0VDC, respectively, whereas ones of logic high and low for the PC correspond to -12VDC and 12VDC, respectively. The MAX232 is used with five 1μF capacitors to adjust the voltage level differences between the PC-based logic and the PIC-based logic. See [7] for more details of the
MAX232 hardware features.
D.
DB-9 Serial Cable
Serial communication between a PIC microcontroller and a PC is performed through a DB-9 serial cable. This cable facilitates data communication between the PIC and the PC. It also allows programming the PIC microcontroller from the PC using serial port programmers.
E.
Personal Computer
In this paper, an IBM-compatible Pentium 4 PC running Microsoft Windows XP operating system is used. As previously mentioned, the PC is used to write, debug, and download embedded PIC programs. One of the serial ports on the PC is reserved for serial communication with the PIC microcontroller. MPASM, IC_PROG, Matlab (version 6.5), and Simulink are installed on the PC. Experimental data is collected and displayed on the PC as well.

F.
PIC Development Board
The PIC development board consists of a photoresistor, a potentiometer, LEDs, a 20MHz crystal oscillator, a MAX232 with five 1μF capacitors, a PIC16F74 microcontroller, a breadboard, and a DB-9 connector. The photoresistor provides light intensity measurement and the potentiometer measures angular position. Those sensors are interfaced to pins allocated as 8bit ADCs in port A of the PIC16F74 microcontroller. The LEDs express digital outputs (on/off) and are connected to pins allocated as digital outputs on port B of the PIC microcontroller. The
PIC microcontroller transmits/receives sensory data to/from the PC via a MAX232 circuit.
III.
S
OFTWARE
E
NVIRONMENT
The software environment for this project consists of the PIC assembly language, Matlab,
Simulink, the predefined DAC toolbox, MPASM, and IC-Prog. The PIC assembly language is a primitive programming language consisting of a 35 single-word instruction set. Matlab is interactive technical computing software. Simulink is Matlab’s model-based, system-level, visual programming environment that is widely used to simulate and analyze dynamic system models using icon-based tools. The predefined DAC toolbox of Simulink provides a library of the PIC microcontroller so that Matlab can interact with the PIC microcontroller. Users, therefore, no longer need to know PIC assembly language to program the PIC microcontroller to be functional.
The PIC library is the predefined Simulink library of additional blocks that are used to communicate data with sensors and actuators connected to the PIC microcontroller. MPASM is an assembler that translates PIC assembly code into PIC HEX code and can be invoked through command line interface. Finally, IC-Prog is a program that can be used to download the PIC
HEX code converted from the PIC assembly code via the MPASM assembler and includes a command line interface. The software interface of our DAC system consists of two main components: i) a Simulink model file named Template.mdl
and ii) a block library named PIC library. Template.mdl
is the Simulink model file where the user designs the Simulink block diagram for interaction with the PIC microcontroller.
A.
Template.mdl
The Template.mdl
model file (see Figure 3) is a predestined Simulink design platform, on which users design the Simulink block diagram for interaction with the PIC microcontroller. The key property of Template.mdl
is the inclusion of a function within the callback parameters of this
Simulink model file, where this function is to be executed before the block diagram actually runs.
Furthermore, renaming this Template.mdl
file still preserves the same callback property, whereas opening a new Simulink model file does not. In our case, when starting the Simulink block diagram, TotalCompile, simulation start function at callback property, is executed at the beginning of each Simulink block diagram cycle. This TotalCompile function performs several important tasks and enables the communication between Matlab and the PIC microcontroller.
Details of this function are provided in a subsequent section.

Figure 3: template and model properties
B.
PIC Library
The PIC Library is a custom library for Simulink which provides blocks (in the form of sfunctions) that interface with sensors and actuators connected to the PIC microcontroller.
Currently available blocks are PIC_ADC and PinStateOut. The PIC_ADC block provides an 8bit digital output from a specified ADC channel of the PIC microcontroller. The PinStateOut block provides the state of a pin (e.g., on or off). Both blocks contain block parameters that need to be set for appropriate hardware configuration. Furthermore, this library contains a block labeled IOBlock which enables serial communication between the PIC microcontroller and
Matlab. The IOBlock is required in all user-designed Simulink block diagrams that will incorporate sensors and actuators connected with the PIC microcontroller. Finally, these blocks are responsible for writing to or reading from global variables, which are to be sent or received from the PIC microcontroller, respectively. Details of these operations are provided in a subsequent section. The following describes hardware settings and parameter requirements of each block.
1) PIC_ADC Block : This block (see Figure 4) configures the analog to digital conversion module of the PIC microcontroller, that is, it allocates an I/O pin of the PIC microcontroller to be capable of analog to digital conversion so that the pin can receive analog inputs from a sensor. A maximum of eight channels are available at port A of the PIC16F74 microcontroller and able to be allocated to receive analog inputs without any needs of external analog to digital converters.
The parameter that the PIC_ADC block requires is a pin number. The pin number is used to assign which I/O pin of the PIC microcontroller to be set to an analog to digital converter.

Figure 4: PIC_ADC block and parameter
2) PinStateOut Block : This block (see Figure 5) configures digital outputs from I/O pins of another port of the PIC microcontroller. Eight channels of port B in the PIC microcontroller are able to be allocated to submit digital outputs. The parameter of PinStateOut block is a pin number.
Figure 5: PinStateOut block and parameter
3) IOBlock: The IOBlock is all the time necessary to every Simulink block diagram so that the
PIC microcontroller is able to interact with sensors and actuators connected. The block first initiates serial communication between the PIC microcontroller and Matlab when it is executed in the beginning. And it sends and receives data between the PIC microcontroller and Matlab while running. Finally it terminates this serial communication link at the end. The IOBlock includes two callback functions in the block properties. These two callback function, start_serial and stop_serial, initiates and terminates serial communication, which are executed when the
Simulink block diagram is started and stopped, respectively. The IOBlock is programmed to have the first priority. Therefore it is the first block executed in the Simulink block diagram. This ensures that all sensor and actuator data in Matlab are first received and sent, respectively, which then is used by the appropriate sensor and actuator blocks in the Simulink block diagram.
Another important role of IOBlock is to provide the sampling period of a given Simulink block diagram. This feature allows blocks that require the sampling period to be used properly, e.g., an integrator block. We denote the sampling period as the amount of time per one cycle of the
Simulink block diagram to be executed. The sampling period provided by IOBlock is an arithmetically averaged sampling period that is calculated by averaging the time taken to run a

specified number of cycles of the Simulink block diagram. The number of cycles used for averaging is user definable, such that the user can adjust the resolution of the sampling period, i.e., the larger number of cycles will provide the finer resolution of the sampling period compared with the smaller number of cycles. However, this arithmetically averaged sampling period does not provide the exact sampling period for each Simulink block cycle. Thus this DAC toolbox is not quite suitable for any real-time requirements, which means enforcing a specific sampling period for the Simulink block diagram is not permissible.
IV.
S
IMULINK
D
IAGRAM
D
ETAILS
This section depicts details in the TotalCompile function and the serial data communication between Matlab and PIC microcontroller. The TotalCompile function is a custom Matlab function which has the sequence of tasks that are performed while a Simulink block diagram is running.
A.
TotalCompile
The TotalCompile function is designed specifically to perform the sequence of tasks. The
TotalCompile function is set as a simulation start function of callbacks function in model properties of Template.mdl
. The TotalCompile function also determines the order of data received from sensors and sent to actuators when a set of sensors and actuators to be used in a
Simulink block diagram. The following subsections describe the sequence of tasks.
1) Using Global Variables: The TotalCompile function declares global variables. The global variables are universally used in every function in order to commonly share data with any sensor or actuator block from the PIC library.
2) Storing Sensors and Actuators Blocks: The next step after defining global variables is looking up all the actuators/sensors blocks by name in the Simulink model file and matching with the ones in the PIC library. When a matching block is found, it is then categorized as either a sensor or an actuator. The matched type of block is then used in conjunction with the specified block parameters to be stored in a data structure depending on its category, e.g., a sensor or an actuator structure. Therefore, for multiple sensor blocks present in a Simulink block diagram, an array of sensor structures is allocated to carry data of the sensor blocks. Similarly, an array of actuator structures is allocated for multiple actuator blocks. On the contrary a “null” object is stored indicating an empty array if there is no sensor or actuator block present in the diagram. It is important that a Simulink model file must be saved every time the Simulink block diagram is modified. Unsaved Simulink model files may not include the most recent updates to the sensor or actuator block parameters in which this sequence of tasks may not be performed correctly.
The sensor/actuator blocks have parameters, which are used to distinguish each block exclusively in case that a Simulink block diagram has multiple blocks with the same name. The parameter of the sensor/actuator blocks is a pin number of the PIC microcontroller connected to the sensor/actuator. The sensor or actuator array information is also applied to organize data sent

via serial communication.
3) Generating PIC Assembly and Matlab Code: In this step, PIC assembly code and Matlab code are generated by using information of sensor and actuator arrays stored in the previous step.
The PIC assembly code generated is used to program the PIC microcontroller. The sensor/actuator blocks in the PIC Library contain corresponding PIC assembly codes. Therefore any sensor/actuator block inserted into a Simulink block provides the associated PIC assembly code. Finally, the PIC assembly code is organized as follows: i) declaration and initialization of
PIC microcontroller functionality, ii) data is gathered from the sensors, iii) sensor data is sent to the Simulink block diagram, iv) the PIC microcontroller waits for Matlab to send the actuator data, and v) this actuator data drives the actuators. Next, Matlab code is generated to facilitate serial communication between Matlab and the PIC microcontroller. In particular, this Matlab code sends and receives the same amount of data that the PIC receives and sends, respectively.
4) Programming the PIC microcontroller: Programming the PIC microcontroller step involves two sequence of steps; i) the generation of corresponding PIC HEX code from PIC assembly code generated in previous step and ii) the programming the PIC microcontroller with this PIC
HEX code via serial communication. The generation of corresponding HEX code process is executed by using the MPASM.exe program, which is provided for free from Microchip Co. and stores the result in a text file. The PIC HEX code is sent to the PIC microcontroller via the PIC-
PG2C programmer using ICPROG.exe program, which has command line programming capacity and is available on the web with free of charge. See [6] for details on how to program the PIC microcontroller in command line via serial communication. Figure 6 shows a flow diagram of programming the PIC microcontroller. After attempting to program the PIC microcontroller using the programmer, the PIC microcontroller has to be removed from the programmer and mounted onto the PIC development board.
Figure 6: Flow diagram of programming the PIC microcontroller
5) Starting a Simulink Block Diagram: When Simulink block diagram starts, the PIC microcontroller will be programmed as previously described. Simulink waits for users to confirm that the PIC microcontroller is removed from the PIC programmer and properly mounted onto the PIC development board once the PIC microcontroller is successfully programmed. Then serial communication between PIC and Matlab starts. If Simulink needs to be run without

reprogramming the PIC microcontroller, then programming the PIC microcontroller procedure can be skipped by clicking “NO” at the step of asking for programming the PIC microcontroller and Simulink will start executing serial communication between PIC microcontroller and Matlab without reprogramming the PIC microcontroller.
B.
PIC microcontroller and Matlab Serial Communication
Since both PIC microcontroller and Matlab provide serial communication capabilities, PIC microcontroller and Matlab communicate with each other using the their serial communication ports. When sensor/actuator data are transmitted through serial communication, those data are carried by units of each packet. Therefore, sensor data in the sensor packet can be retrieved by the corresponding sensor blocks in the Simulink block diagram, whereas data from the actuator blocks are packaged into a single actuator packet for transmission to the PIC. The reason why packets are used for data communication between Matlab and PIC is because of efficiency compared with the individual transmission of sensor/actuator data. By transmitting sensor/actuator data in packets form, the amount of information needed to be carried with the data via serial communication is reduced, i.e., in each sensor or actuator packet, the necessary data for serial communication is only one start and stop bit, whereas for individual, disjoint sensor or actuator data, multiple start and stop bits are necessary for serial communication.
The IOBlock receives the sensor packet and stores the data in a sensor global variable. The sensor packet received from the PIC is first converted to the appropriate sensor data, i.e., a numerical value dependent on the sensor type, and is then stored in the sensor global variable.
The IOBlock transmits data from the actuator global variable to the PIC for execution. In constructing the actuator global variable, each actuator block converts the numerical value of their actuator data into a set of bytes. Next, the sets of bytes for all actuator blocks are packaged into a packet and saved into the actuator global variable. Lastly, data communication between
PIC and Matlab will continue until the Simulink block diagram is stopped.
V.
E XAMPLE
–
DC M OTOR C ONTROL
This example explores a DC motor control experiment using the PIC microcontroller and our
Matlab data acquisition and control toolbox. The DC motor test-bed, shown in Figure 7, consists of a DC motor, a continuous rotation potentiometer, and an H-Bridge. The potentiometer sensor measures angular position of the DC motor and is used in the feedback control algorithm. The potentiometer outputs a +5VDC signal corresponding to the absolute angular position of the motor. The position of the DC motor is sent to Matlab as an analog signal converted by the microcontroller using an ADC pin. The PIC microcontroller supplies logic signals to the operate
H-Bridge to control the DC motor angular position.
In this experiment, we used Matlab version 6.5, which has a built-in serial communication library, in addition to Simulink version 5.0. This experiment utilizes the on-off controller using deadband to control the position of the DC motor. Referring to Figure 7, a PIC_ADC block is used to import sensor data to the PIC microcontroller. The output from a sensor block is then connected to an appropriate calibration gain block. Furthermore, PinStateOut blocks are used to transmit H-Bridge controller logic output to control position of the DC motor. We note that in this Simulink block diagram an IOBlock from the PIC library is used to obtain the sampling

period.
Figure 7: Hardware layer schematic
A.
Experimental Results
A sliding mode on-off controller is implemented in Simulink to control the DC motor using the PIC Library. In this experiment, we command the DC motor arm to track set points between
90 degrees and -90 degrees, which produced a 2 percent settling time of 1.37sec. Figure 8 shows the DC motor position response.
Figure 8: DC motor position tracking response
VI.
C
ONCLUSION
In this paper, we exploited the serial communication capabilities of Matlab and the PIC microcontroller to develop an inexpensive data acquisition and control system. Using the advanced features of Simulink, our software environment allows for the generation of PIC assembly code for a variety of sensors and actuators, programming of the PIC microcontroller, and data communication between PIC and Matlab. Furthermore, a DC motor control experiment was conducted to show the salient features of our data acquisition and control toolbox.
Specifically, a sliding mode on-off controller was implemented in a Simulink block diagram to

control the DC motor arm position.
R
EFERENCES
[1] S.-H. Lee, Y.-F. Li, and V. Kapila, “Development of a Matlab-Based Graphical User
Interface for PIC Microcontroller Projects,” Proceedings of the American Society of
Engineering Education Conference, Salt Lake City, UT, Session 2220, 2004.
[2] Y. F. Li, S. Harari, H. Wong, and V. Kapila, “Matlab-Based Graphical User Interface
Development for Basic Stamp 2 Microcontroller Projects,” Proceedings of the American
Control Conference, Boston, MA, pp. 3233–3238, 2004.
[3] A. Panda, H. Wong, V. Kapila, and S.-H. Lee, “Matlab Data Acquisition Control Toolbox for
Basic Stamp Microcontrollers,” Proceedings of the Conference on Decision and Control, San
Diego, CA, 2006.
[4] Online: http://www.microchip.com/1010/index.htm, website of Microchip Technology, Inc.
[5] Online: http://www.olimex.com/dev/, website of Olimex Ltd., (access link for PIC-PG2B
Development Programmer).
[6] Online: http://www.ic-prog.com/, website of IC-Prog software developer of the PIC microcontroller programming (access link for the command line programming for PIC microcontrollers).
[7] Online: http://pdfserv.maxim-ic.com/en/ds/MAX220-MAX249.pdf, website of Maxim
Integrated Products, (access link for MAX232 datasheet).
[8] Online: http://www.mathworks.com/products/simulink/, website of MathWorks Inc., developer and distributor of Simulink.