Tutorial: Open Loop Speed Control of a DC Motor via 8255 Controller using TCP/IP Server-Client Application Programmed in Visual Basic

Introduction

In today’s demanding environment of industry, it is required to control and monitor operations remotely, which is beneficial in terms of cutting cost and down time of the operations. Devices, which communicate via TCP/IP Server-Client operations, are one of the best candidates for these operations.

This Tutorial is intended to cover: Open Loop Speed Control of a DC Motor via 8255 Digital I/O Controller chip using TCP/IP Server-Client Application Programmed in Visual Basic. The 8bit DAC0832 chip is used as the Digital to Analog Converter.

Proposed Solution

In this project open loop control of a DC motor will be established using a power amplifier, a digital to analog converter, 8255 digital interface card, a client PC and a Server PC. The DAC circuit, which is controlled by the server computer via 8255 digital interface, will be used to control the speed of a DC motor by changing the voltage going to the base of the power amplifier. The voltage going into the motor from the power supply is between 0 and +5V. The role of the power amplifier circuit is to provide the current necessary, to operate the motor. The client computer, communicates with the server computer via Ethernet communications and it is the GUI interface to control the speed of the motor. There can be several client computers hooked up to the server, however, for this application there is only one. The winsock component is used in the Visual Basic code to provide the server/client operations.

In Summary, this appliance has four main components:

Server Software - to interface with the mechanical device, and the internet
Client Software - to interface with the user, and the internet
8255- to output the 8-bit digital number
Digital to Analog Converter – to convert the 8-bit digital number into a 0-5VDC voltage.
Power Amplifier- to regulate the current going into the motor.
Motor- to give the required torque at the required speed

Procedure

Parts

Table-1 Internet Appliance Electro-Mechanical Parts
Part	Vendor	Part #	Quantity	Price
DAC-0832 8 bit DAC	Jameco	128186	1	$3.95
Diode (1N4003)	Jameco	76970	8	$0.04
LF353 Op-Amp	Jameco	22939	1	$0.39
10Kohm Resistor	Radioshack	271-1335	1	$1.27
8255 Card	Boondog.com	8255 Kit	1	$59.00
20Kohm Resistor	Radioshack	271-0265	2	$49.99
100 ohm resistor	Radioshack	271-1311	1	$4.22
Breadboard	Radio Shack	276-174	1	$13.49
DC Motor	Mabuchi	RE-280RA-20120		$1.27
0.01uF Capacitor	Radio Shack	272-1051	1	$13.49
TIP31 Power Transistor	Jameco	33048	1	$0.49
Wrapping Wire	Radio Shack	278-501	1	$2.99

Construction

This internet appliance calls for several electro-mechanical components: An 8255 card to interface the server PC with the dc motor control circuits. The 8255 card`s purpose is to provide an interface between the server PC and the dc motor control circuits. More information on the 8255 card's construction and operation may be found at www.boondog.com.

Figure-1 Schematics of the System

The DAC-LF353 op amp circuit provides the proper voltage to the TIP31, which regulates the current coming from the power supply. The circuit is built so that it would output voltage ranging between –5V to +5V.
The TIP31 circuit is a power amplifier, which allows current to flow from Collector through the Emitter pin proportional to the voltage on the Base pin. The illustration of the motor is given in Figure-2.

Figure-2 Illustration of the DC motor

Software

The software to control this internet appliance is broken into two groups: Software on the server PC and software on the client PC.

Server

The purpose of the server is to interface the internet appliance with the internet.

Figure-3 Screen Shot from the Server Application

The server has several software components:

Visual Basic software to communicate with the client through WinSock, and to communicate with the 8255 Card through the 8255.dll.
The visual basic software may be downloaded below:

Client

The purpose of the client is to interface the user with the appliance through the internet.

Figure-4 Screen shot from the Client Application

The client has several software components:

Visual Basic software to communicate with the server through WinSock, and to communicate with the user through a GUI.
The visual basic software may be downloaded below:

Turbo C

To demonstrate the functionality of the circuit before investing time into writing the server and client software, a TurboC code has been written.

This code:

Prompts the user for the address of the 8255 card.
Prompts the user for the a digital number
Runs the motor at the speed which corresponds to the digital word.

You may download this code below:

TurboC Source Code

Theory of Operation

The velocity command (RPM) is passed between from the client to the server using WinSock TCP/IP. The velocity command is then converted into a digital number and output to the DAC via Port A of the 8255 digital interface.

In this experiment, as the speed of the motor is altered, the following parameters are monitored:

1. 1. Voltage in to the motor (Vin): This parameter is measured while the motor is not connected to the circuit.

2. 2. Motor Speed in Hz: This parameter is measured using the IR circuit and the oscilloscope as explained in Section 2.

3. 3. Motor Speed in RPM: This parameter is evaluated from the Motor Speed measured in Hz.

4. 4. Back EMF: This parameter is measured from the tachometer while the motor is driving the inertial load.

5. 5. Motor Current: Motor Current is monitored across the terminals of the motor used as a tachometer using a 100 Ohm resistor wired in series.

Figure-5 Voltage vs. Digital Word Graph

Figure-6 Back EMF vs. Speed Graph

Figure-7 Current vs. Speed Graph

Figure-8 Speed vs. Voltage Graph

Operating Procedure

These steps must be taken in the following order to successfully run the Internet appliance:

· · Start Up Procedure:

Connect appliance to the server PC.
Confirm network connectivity between server and client PCs.
Start the DC Motor Server software on the server PC.
Start the DC Motor Client software on the client PC.
Turn on the power supply
Enter the server PC's IP address when the Stepper Control Client software requests it.
Utilize appliance.

· · Shut Down Procedure:

Shut down the power supply
Close DC Motor Client software.
Close DC Motor Server software.

Conclusion

Utilization of remote appliances over the Internet or Local Area Networks has many advantages, which can be listed as:

Expensive and rare pieces of equipment may be brought closer to users all over the world. This allows those who cannot justify purchasing equipment to use it after an agreement is made with a host organization.
Organizations considering purchase of expensive equipment may be able to diffuse the cost of the equipment through renting time on the machine over the Internet. The customer base for this use is of course worldwide.
In the considerably large facility, such as a power plant, there will be applications, which require controlling and monitoring on a constant basis. In these plants there maybe networks, which is, consist of several server and client computers.
One of the good examples of the using the server client architecture in a controls/monitoring environment is vibration-monitoring systems used in industrial plants. These consist of accelerometers attached to the critical components to determine the faults before they occur. There are several data acquisition modules and server PCs acquiring data on a constant basis and taking the FFT and doing a trend analysis. The client computer retrieves this data and makes decisions like issuing alarms or shutting down the related part of the plant.

Cagdas YILMAZ is a graduate student in the Department of Mechanical Engineering at Drexel University.