ROLLING LED DISPLAY WITH COMPUTER

INTERFACE.

A PROJECT BY:

GADRE NAYAN GOKHALE PRANAV JOSHI RAVISEN JOSHI SARANG

INTRODUCTION: Short and long notices are a very common sight on sponge boards and sometimes they are even glued onto walls. With so many notices around it becomes difficult for the reader to quickly point out the most important detail.

The dot matrix moving sign module has a six character display area which can be used to highlight the important points in a decorative fashion by moving the information around giving it a good aesthetic value. PC interface allows the user (the administrator ) to change the details to be displayed by just sitting in front of the PC . A visual interface also provides good aesthetics.

Moving signs are a common enough sight today but off-the-shelf units are invariably expensive and somewhat inflexible. The six-character module which we are presenting here can be cascaded up to 16 modules long and has a character set that can be customized to suit your application.

BLOCK DIAGRAM:

LOGIC: A separate 5-V mains unit supplies power for this module. Each displayed character is made up of a 5×7 LED matrix. Assuming that each LED requires a current of 10 mA, this gives us a worst case current consumption of 350 mA for each character. Multiplying this value by six for the six characters of each module may cause fear for a hefty power supply. In order to reduce the current required for the module and to simplify the hardware and wiring necessary to drive the LEDs this design uses multiplexing. This technique switches on the driver transistor for each horizontal row of LEDs in the switched quickly enough then your eye will not see the flickering and they will appear to be continuously lit. The trade-off is that because each row of the character is only on for one seventh (in practice less) of the time that it would be if it were continuously lit, the display will not appear as bright. In practice the LED driver must also be blanked while each new row of information is shifted into the display shift register

To offset the reduction in display brightness the LED current has been increased. Looking at the circuit diagram shown in it can be seen that the column information for the display LEDs is supplied by the outputs of the six shift register ICs type 74LS164. Only five outputs are used on each shift register. The seven display matrix rows are selected by the three outputs of the microcontroller (P1.0 to P1.2) which control a one of-eight decoder type 74LS138 (IC2). Port 1.7 is the data signal while P1.6 produces the clock signal. The reset inputs to the shift registers are not used in this application it would have the effect of turning on all the LEDs in the matrix. The display process begins by the controller selecting the ’invalid’ line 8 output of the display line driver (IC2). The effect of this is to turn off all the LEDs. This is necessary to blank out the passage of serial data through the shift registers which would otherwise cause all the LEDs to flicker dimly. The microcontroller will take the ASCII code of the character to be displayed from its internal memory and uses this value to access its corresponding display pattern in a character generator. The controller will then take the first line of the display pattern and send it out serially to the display shift registers. Any bit in the pattern that is ‘1‘ will turn the LED off, any bit that is a ‘0‘ will turn the LED on

. The controller also generates the clock to transfer this serial data into the shift registers. This process is repeated for the first line of the other five display characters. After this the transistor driving the first row (R1) is enabled. All of the shift register outputs that are low will cause these LEDs in the first line to light for a short period until the row driving transistor is turned off. The same process is now repeated for the second row up to the seventh when the whole process is repeated .This is repeated until the PC sends a new character.

CIRCUIT SPECIFICATIONS: Resistors: R1-R5 = 10kΩR6, R38-R44 = 2k2R7 = 33kΩR8-R37 = 330Ω Capacitors: C1, C2 = 18pFC3, C4 = 10F 16V radialC5, C6, C7 = 100nF

Semiconductors: D1 = 1N4148LD1-LD6 = TC12-11SRWA or TC12-11HWA T1 = BC547T2-T8 = BC640IC1 = 89C4051-24PC, programmed,IC2 = 74LS138IC3-IC8 = 74LS164 Miscellaneous: S1 = 4-way DIP switchX1 = 11.0592Hz quartz crystalRS 232DB 9P CONNECTOR

ELECTRICAL SPECIFICATIONS:

Power supply required : 5V. Current requirement for each LED: 10mA max. Current requirement for LED matrix: 350mA max RS 232 SPECIFICATION

Cabling Single-ended Number of Devices 1 transmit, 1 receive Communication Mode Full duplex Distance (max) 50 feet at 19.2kbps Data Rate (max) 1Mbps Signaling Unbalanced Mark (data 1) -5V (min) -15V (max) Space (data 0) 5V (min) 15V (max) Input Level (min) ±3V Output Current 500mA (Note that the driver ICs normally used in PCs are

limited to 10mA) Impedance 5k? (Internal) Bus Architecture Point-to-Point

MECHANICAL SPECIFICATIONS: MATRIX SPECIFICATIONS: Matrix height : 2.094 Breadth: 1.496 Thickness: 0.339 Diameter of each LED: 0.197

PCB SPECIFICATIONS: 9”X3.5”

(All dimensions are in inches)

CIRCUIT DIAGRAM:

MODULEWISE DESIGN:

REGULATED POWER SUPPLY: The +5 volt supply is useful for both analog and digital

circuits. DTL, TTL, and CMOS ICs will all operate nicely from a +5 volt supply. In addition, the +5 volt supply is useful for circuits that use both analog and digital signals in various ways. More importantly for our purposes, the +5 volt supply will be used as the primary reference for regulating all of the other power supplies the we will build. We can do this very easily if we use operational amplifiers as the controlling elements in the power supply circuits. We'll see how this works after completing the basic +5 volt supply.

T1

IRON_CORE_XFORMER

C21mF

C110uF

U1

DC 10MW

4.998 V+ -

V2

230 Vrms 50 Hz 0°

3

5

U3LM7805CTLINE VREG

COMMON

VOLTAGE 1

C310nF

6

D51N4148

D1

1N4148

D21N4148

D31N4148

7

2

8

0

The +5 volt power supply is based on the commercial 7805 voltage regulator IC. This IC contains all the circuitry needed to accept any input voltage from 8 to 18 volts and produce a steady +5 volt output, accurate to within 5% (0.25 volt). It also contains current-limiting circuitry and thermal overload protection, so that the IC won't be damaged in case of excessive load current; it will reduce its output voltage instead. The 1000µf capacitor serves as a "reservoir" which maintains a reasonable input voltage to the 7805 throughout the entire cycle of the ac line voltage. The two rectifier diodes keep recharging the reservoir capacitor on alternate half-cycles of the line voltage, and the capacitor is quite capable of sustaining any reasonable load in between charging pulses. The 10µf and .01µf capacitors serve to help keep the power supply output voltage constant when load conditions change. The electrolytic capacitor smooths out any long-term or low frequency variations. However, at high frequencies this capacitor is not very efficient. Therefore, the .01µf is included to bypass high-frequency changes, such as digital IC switching effects, to ground.

The +5 volt power supply is based on the commercial 7805 voltage regulator IC. This simplifies the design and layout of the circuit considerably, because all of the regulating circuitry as well as current limiters and overload protection are built into the IC. As a result, little is needed in the way of support circuitry.

We do still need the external capacitors. One thing that is very difficult to achieve in ICs is a capacitor of high capacitance value. Therefore, the electrolytic capacitors must be provided to work with the IC. The disc ceramic capacitor must also be of a higher value than is readily obtainable within an IC, so it, too, must be provided externally. The resistor and the LED pilot light are not necessary for the correct operation of the power supply. However, they do serve to indicate when power is on, and also help to discharge the 1000µf reservoir capacitor when power is turned off.

RS 232 : Where RS stands for "recommended standard." Due to its relative simplicity and low hardware overhead (when

compared to parallel interfacing), serial communications is used extensively within the electronics industry. Today, the most popular serial communications standard is certainly the EIA/TIA-232-E specification. This standard, which was developed by the Electronic Industry Association and the Telecommunications Industry Association (EIA/TIA), is more popularly called simply RS-232, where RS stands for "recommended standard." Although this RS prefix has been replaced in recent years with EIA/TIA to help identify the source of the standard, this paper uses the common RS-232 notation.The RS-232 standard also limits the maximum slew rate at the driver output. This limitation was included to help reduce the likelihood of crosstalk between adjacent signals. The slower the rise and fall time, the less chance of crosstalk. With this in mind, the maximum slew rate allowed is 30V/ms. Additionally, standard defines a maximum data rate of 20kbps , again to reduce the chance of crosstalk. The impedance of the interface between the driver and receiver has also been defined. The load seen by the driver is specified at 3k? to 7k?. In the original RS-232 standard the cable length between the driver and receiver was specified to be 15 meters maximum. Revision "D" (EIA/TIA-232-D) changed this part of the standard .

MICROCONTROLLER (AT89C4051): The RS 232 interface PC & microcontroller . In this application

data flows in one direction only so a simple transistor is used as the most economical solution. Input resistor R7 is used to limit the input current when the PC drives the data line high.

A four-way DIP switch (S1)defines the binary coded address of the module and is read by the controller at port pins P3.2 to P3.5.

Diode D1 limits the negative input voltage at the transistor to approximately minus 0.7 V when the data line is driven low. Transistor T1 inverts the signal on the data line and applies it to input port 3.0 of the microcontroller. This design operates without any handshaking protocol between the PC and the display module, but it is still necessary to connect the unused pins of the COM port to the correct signal levels so that the PC knows that the module is always ready to receive data. For 9 -pin connectors it is necessary to link pin 7 with pin 8 and also to link pins 1, 4 and 6 . Figure shows the details of com port connections.

Communication from the PC to the module takes place at 9600 baud rate with no parity bit, 8 data bits and one stop bit. The microcontroller clock is supplied by a standard 11.0592MHz crystal (X1). Other crystals can be used but this would require a change to the initialization routine of the microcontroller. The complete module is powered from a single 5 V power supply Port 1.7 is the data signal while P1.6 produces the clock signal.

5-1V-(0.4) R-(3.0)=0R=2.5kΩ

DESIGN FOR BC 640:

5-0.5-1.2-I*R-0.1=0R=320Ω (considering 10 mA current)

IC 74LS138 (3:8 decoder): The row addressing is performed by the

decoder IC. The 3 i/ps to the decoder are from microcontroller ports P1.0, P1.1, P1.2. The decoder outputs are active low, they are applied to the PNP transistors. Each transistor collector is connected to the anodes of a complete row of LEDs.

LED MATRIX DISPLAY:

The pins 1, 2, 5, 7, 8, 9, 14 of all LED display are shorted. These are used for row switching through IC 74LS138The shift register inputs are given to the pins 3, 4, 6, 10, 13 of each LED matrix .These are some samples,

1 1 1 0 0 0 0 01 1 1 0 1 1 1 11 1 1 0 1 1 1 11 1 1 0 0 0 0 11 1 1 0 1 1 1 11 1 1 0 1 1 1 11 1 1 0 0 0 0 00 0 0 0 0 0 0 0

1 1 1 1 0 0 0 11 1 1 0 1 1 1 01 1 1 1 1 1 1 01 1 1 1 1 0 0 11 1 1 1 1 1 1 01 1 1 0 1 1 1 01 1 1 1 0 0 0 10 0 0 0 0 0 0 0

1 1 1 1 1 1 1 11 1 1 1 1 1 1 11 1 1 0 1 1 1 01 1 1 0 1 1 1 01 1 1 0 1 1 1 01 1 1 0 1 1 0 01 1 1 1 0 0 1 00 0 0 0 0 0 0 0

• SHIFT REGISTER (74LS164):

Clock to the all shift register is given from microcontroller Port P1.6. From datasheet we can see that , the pin no. 1&2 are shorted to give serial input. We are using same concept. Data input is first given to the rightmost shift register. The shift register we are using is serial in parallel out shift register. We are using pin numbers 3, 4, 5, 6, 10 as parallel output .These 5 outputs are respectively given to the LED matrix pin numbers 6,10,4,3,13 respectively. The shift register is used to shift the data in column from left to right . The pin no. 10 of the rightmost shift register is given as serial input to the next shift register, that is shorted pin no.1 and 2 .this connection is done for all 6 shift registers. In this way, data shifts from right LED matrix to the left LED matrix.

We have used ‘Visual Basic 6.0’ software to display window where user can enter the text he wants to display. The window displayed on computer screen is as follows.

LITERATURE SURVEY:Muhammad Ali Mazidi and Janice Gillispie Mazidi, The 8051

microcontroller and embedded systems.Kenneth J. Ayala , 3rd Edition, The 8051 microcontroller.Block diagram, Rolling display using matrix LEDs,

www.projectsof8051.com/projects/06-rolling-display.Electronics For You ,April 2009 edition. www.alldatasheets.com www.edaboard.com www.punzelek.com www.elektor.com http://www.maxim-ic.com/support