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Part 4 Build your own LED Message Board In this final article, we show you how to build and test the display panel. We also tell you how to use the system and list the control commands that provide all the special effects. Design by DON McKENZIE As noted in previous articles, the display is made up of four printed boards, each accommodating 24 columns of LEDs (168 in all). To simplify the description, we will assume that you are going the whole hog and building a 4-board display. The procedure for building each display board (DIS5MM) is the same. Before installing any components 70 SILICON CHIP on the display board, carefully check it out on both sides for shorts or open circuit tracks. Use your multimeter to check that the ground and + 5V lines are not shorted together. It is very important to follow the correct order of assembly for the display panel. If you install components in the wrong order you will •find that others cannot be fitted. Supplied in the short form kit for the LED Message Board is a LED alignment tool. As its name implies, this is for aligning the LEDS so that they are all evenly positioned to give the professional finish that a good message board deserves. There are four holes on the perimeter of the LAD (LED alignment device) which are sized so that ½ -inch long Va-inch BSW screws can be self-tapped into them. These locate the alignment tool over the DIS5MM circuit board. Spray job The DIS5MM printed circuit board has to be sprayed black before soldering anything to it. Tape the bottom 20mm of the circuit board, where the ICs are, with a piece of masking tape and lightly spray the board with quick drying matte black paint. This is done so that reflections from the LEDs will not degrade the display. Spraying may have to be done several times. Several light, even coats are better than one heavy coat which will clog up the solder holes. It is most important that all LEDs are the same type number so that there are no inconsistencies in colour or brightness between each LED. It is also very important that the LEDs have an intensity somewhere between 7-10 mcd (millicandela) and a viewing angle of 36 degrees or greater. Most red LEDs that you would buy off the shelf would be 0.8 mcd which is totally unsuitable for the job whereas most green or orange types are 8.7 mcd (the range is very broad, starting at about 0.8 mcd and going to 350 mcd, or even higher). Do not buy high intensity LEDs as they have a typical viewing angle of only 15 degrees which is unsuitable. If your store owner cannot tell you the intensity and viewing angle of the LEDs then don't buy them as it is a murderous job to desolder all those LEDs once they are in the PCB. Typical examples of suitable LEDs are the Liton brand LTL-4223 (red), LTL-4233 (green) and LTL-4293 (orange) which all have an intensity of 8. 7 mcd and a viewing angle of 36 degrees. One last point: buy all your LEDs at once, even if at first you are go- One of the 7 x 24 LED panels. The header socket is on the copper side of the board. Note that the component side of each LED board is painted black to provide enhanced contrast and prevent reflections. ing to build just one panel. as you may not be able to get the same type again at a later date. Now comes the fun part! Starting from the left hand side of the panel insert a 7 x 7 matrix of LEDs with their ea thodes towards the bottom of the board (ie, towards the ICs). You may find that some brands of LEDs have large tangs on their legs which wont pass through the holes in the PCB. Don't worry - providing they are all the same height, it does not matter whether the LEDs are sitting flush with the circuit board or are slightly raised. Carefully position the LED alignment tool over the matrix of LEDs and lightly finger tighten some nuts onto the screws protruding on the underside of the display board to hold the tool in place. The panel can now be turned over without fear of dropping any LEDs or disturbing their position while they are soldered in place. After doing two lots of 7 x 7 LEDs, start on the righthand side of the board and that should leave just a 3 x 7 matrix in the middle to finish off the panel. The 2 x 26-pin dual row male header pins may now be soldered in but be careful as they are inserted from the solder side of the circuit board. This is because connections to and from the panel are made via headers and cables from the back of the board. Note that Jl and JZ are the only components mounted on the solder side of the board. The 24 330 ½ -watt resistors can Fig.I: a LED alignment tool (supplied with the short form kit) is used to accurately position the LEDs on the PC board. The two header sockets must be installed on the copper side of the board before the 33rl resistors are installed. J2 OUTPUT ON OTHER SIDE OF BOARD JI INPUT ON OTHER SIDE OF BOARD JUNE 1989 71 PARTS LIST FOR LED DISPLAY PANEL 1 PC board designated DIS5MM (available from Don McKenzie 1 perspex channel (available from Don McKenzie) 1 baseboard, 29 x 3.5 x 0.75-inch 2 26-way dual-row male header strips 7 1 4-pin IC sockets 1 68 5mm LEDs, all same colour and intensity Integrated circuits E1 ,E3,E5,E7 - 75492 hex inverting buffer E2,E4,E6 - 7 4LS164 serial in/parallel out shift register The four LED panels are "daisy-chained" together via the Jt and J2 header sockets on the copper side of the boards. Passive components BC1-BC6 - .01 µF ceramic capacitors R1-R24 - 330 ½W resistors Note: multiply all parts by 4 for the full 4-panel (16-character display). The Jt header on the rightmost panel is connected to the control unit via a 25-way cable terminated with a header socket and DB-25 connector. now be installed but take care to provide clearance when installing the resistors that go over the solder pins of Jl and J2. Install the 6 .OlµF ceramic bypass capacitors and the 7 sockets for the ICs, taking note of the orientation of pin 1 in each case. Now install the ICs into their respective sockets and that completes one display panel. If you are building more than one panel it will necessary to repeat the above procedure. With the panels completed, you 72 SILICON CHIP can link them together via short 26-way header cables by way of the Jl and J2 header pins. Note that when the panels are butted up next to each other with the ICs towards the bottom, the main connection from the controller will connect with Jl on the righthand side panel and will then be daisy-chained through the other panels. You can now apply the power and you should see the default ROM based test message cycling thr,ough on the display panel. Adjust the 50k0 trimpot on the interface board till you get the most stable display in both static and moving display modes. The recommended method of housing four panels is as follows: Cut a sheet of 19mm particle board as shown in the diagram and drill 16 1/s-inch holes so that the display panels can be mounted on 25mm spacers. Cut a small section away so that access can be gained to Jl on the righthand panel. If you can accurately cut this board to the dimensions shown it should fit snugly into the grey tinted acrylic housing which is available from the designer, Don McKenzie. Operator Instructions The moving message board will accept a message that can-be either a straight ASCII message or it can have some control codes (entered with the Ctrl key) embedded into the message string. These control codes will enable various attributes to be added to the message. A complete list of these attributes is included below. As noted previously, there are two ways of entering a message into the moving message board. The The LED display panel is covered by a grey Perspex channel which is suitable for all LED colours. A ready-made channel can be ordered from the designer, Don McKenzie, for $50 plus $15 p&p (see panel). 0.75" THICK PARTICLE BOARD 16x1/B" HOLES 0.4" 6.6" 6.6" CUT OUT TO SUIT CABLE 6.6" 6.6" 0.6" 118" ACRYLIC SHEET CUT TWO END CAPS TO SUIT AND GLUE AT EACH ENO Fig.2: here are the dimensions for the baseboard and the perspex channel for the display board. Note that all dimensions are shown in inches. first way is to hook up a personal computer which has a Centronics parallel printer output to the female Centronics plug on the back of the controller. Be sure to switch the front panei toggle to the computer position. Data can then be loaded into the message board by sending the data down the printer port. An easy way to do this is to use a wordprocessor or similar text editor which produces ASCII text (Wordstar is not suitable). Type your message and then embed the JU N E 1989 73 control characters depending on the way you wish your message to be displayed on the moving message board. Then just print the file as if it was going to a printer and you should see your message appear on the display. The other method is to connect an IBM PC XT or compatible type keyboard to the 5-pin DIN plug on the back of the controller. When using the keyboard method, you enter the EDIT mode by pressing HOME. This gives a static display of the first 16 characters of the current message starting at the left column and any control characters that are embedded in the message will be shown as flashing characters. The message board software supports 11 message buffers that will enable you to store up to 10 messages of your own plus the default ROM-based test message. You can select which message buffer you wish to be active by pressing one of the function keys. Fl gives you buffer 1, F2 gives buffer 2 and so on. You should see a flashing full block on the 1st character in the message. This is the display cursor. This can be moved back and forth by the keyboard cursor keys. You need to go into Insert mode for editing. The Up or Down cursor keys will jump forward to the next screen or to the prior screen, while the Home and End cursor keys will jump to the Start or Finish of the message and the cursor will be flashing on the 1st character on the lefthand side of the display. By using these keys you will be able to quickly move about the message string to do editing. The initial edit mode is the Overwrite mode which will accept any characters typed on the keyboard and overwrite them onto the existing message. This mode is indicated by a full block cursor. If the INS key is pressed to go into the edit mode, this is indicated by a flashing half-block cursor. The INS key will toggle between these edit modes and the DEL key will Delete the character shown under the current cursor irrespective of whether you are in the Insert or Overwrite mode. 74 SILICON CHIP Keyboard Commands Home: keyboard attention; stops the current display and enters Edit mode on the current buffer at the first character. ESC: run current buffer. After you are happy with your editing this will display the current message. F1·F10: selects the specified buffer tor editing. Ctrl 0: displays the ROM test message buffer. Note that this cannot be edited. Ctrl 1 to Ctrl 4: selects the number of panels that you wish to use from 1 to a maximum of 4 panels. (Note: the power up default is 4 panels). Ctrl 8: tests the type of IBM keyboard that is connected and displays this in buffer 1 0 (there are 3 types supported). Ctrl 9: copies the ROM test message into buffer 1 . Ctrl F1 to Ctrl F10: erases the specified buffer . DEL: deletes the character under the cursor. INS: toggles the insert mode on and off. END: jumps to the end of the current buffer. UP-arrow: moves to the next page. ON-arrow: moves to the previous page. RT-arrow: moves cursor right one position. LT-arrow: moves cursor left one position. Note: buffers 1 and 2 are each 2K bytes long and are also used to capture the input from the Centronics input and juggle appends etc. Therefore, anything in this buffer will be lost when sending a string via the computer. Buffers 3 to 1 0 are each 256 bytes long. Control Commands Ctrl A: this will append the new message to the old. Ctrl C: this clears the board and erases the current message from memory. Ctrl D: this will load the new message immediately; ie, will not finish current message. Ctrl Ex: this will enable the 'screen dump' filter to be changed. See note 1. Note: the above commands only apply to the Centronics input and are not applicable to keyboard input. Ctrl F: this will toggle the Flash mode ON and OFF. Ctrl Gx: this will pause and Flash the display tor "x" seconds. See notes 2 & 3. Ctrl I: this is the Tab character which is displayed as 4 spaces. When you are finished editing your message just press the ESC key and your message should start to move onto the display board. The absence of any Control character will display the new message after the last has finished its cycle. A list of the Control (Ctrl] commands that can be embedded into the text string is shown in the accompanying table. Note that each line to be displayed must have a full 16 characters of text when control characters are embedded, otherwise the display will not work correctly. If necessary, the line can be padded with spaces to make up the necessary 16 characters. Finally, note that some commands must be embedded as leading attributes while others are embedded as trailing attributes. These are listed in the table. ~ Ctrl J: this is the LF (linefeed) character which is ignored by the moving message display. Ctrl L: this is the FF (formfeed) character. See note 1 . Ctrl M: this is the CR (carriage return) character. See note 1. Ctrl N: this will show the next message as a static display after the old message is finished. Ctrl 0: this command will shoot the message one character at a time onto the screen from the right (shot on). Ctrl Px: this command will pause the display for x seconds. See notes 2 & 3. Ctrl Q: this command will clear the board by moving the display across to the right (exit stage right). Ctrl R: this command will toggle the display between large (twice normal size) and normal characters. Ctrl T: this command will display the next screen by scrolling the text down and over-writing the old screen (wipe down). Ctrl U: this command will display the next screen by scrolling the text up and over-writing the old screen (wipe up). Ctrl V: this will display the next screen by scrolling the text down, pushing the old screen as it goes (roll down). Ctrl W: this will display the next screen by scrolling the text up, pushing the old screen as it goes (roll up). Ctrl X: this will display the next screen by wiping over the old screen to the left (wipe back). Ctrl Y: this command will display the next screen by wiping over the old screen to the right (wipe forward). Ctrl Z: this is the EOF (end of file) marker and is the normal message terminator and cannot be created or overwritten while in Edit mode. Note 1 : with the Ctrl E command to enable the screen dump filter, certain characters will be translated as follows: (a) with Ctrl E0, CR and FF are ignored; spaces are as ordered. (b) with Ctrl E1, CR is translated into a Tab , FF is translated into a Tab; spaces are limited to a maximum of four spaces . Note 2: some commands require a numerical parameter to be included for a time delay in seconds: 0 = ½ second delay; 1 = 1 second, 2 = 2 seconds, up 9 seconds delay. Note 3: As the Ctrl Gx and Ctrl P commands are applicable to the entire screen they are 'trailing attributes'; ie, the message is sent first then the attribute is sent. Note 4: Ctrl T, U, V, W, X and Ctrl Y are 'leading attributes' which affect the whole screen. Note that each line to be displayed must be padded with spaces to a full 16 characters for the line to be displayed correctly. IX-A-KIT Kit Repairs - $15 per hour. Normal Rate - $30 per hour. No charge for kits that can't be repaired. 3 month Warranty on repairs . Construction - fixed or hourly 1 2 Month Warranty on Manufactured Kits. Custom Designing , Manufacturing, Large or Small Quantitites . YCAL ENTS Design, Manufacture, Repair of Electronic Equipment. (02) 633 5897 Unit 4, 62 Great Western Highway, Parramatta, NSW 2150. Trading hours: 8am to 3pm Monday to Friday. D.DAUNER ELECTRONIC NTS WE STOCK A WIDE RANGE OF ELECTRONIC PARTS • * for Development • Repair • Radio Amateur • Industrial Electronic • Analog and Digital WHILE STOCKS LAST THE FAMOUS TR-DIP METER (as featured May '89) $98.00 * CRO-VALVE 3ACP2A $45.00 * PHILIPS IR-IMAGE CONVERTER Where to buy the parts A complete set of printed circuit boards plus the programmed 2764 EPROM and full instructions are available from the designer, Don McKenzie , for $150. The specially made grey Perspex channel, suitable for all LED colours , is also available from Don McKenzie for $50 plus $1 5 for packing and postage. Write to Don McKenzie, 29 Ellesmere Crescent, Tullamarine, Victoria 3043 . All the semiconductors and other parts are readily available from parts suppliers such as Jaycar Electronics, Dick Smith Electronics, Altronics , Geoff Wood Electronics and David Reid Electronics. VALVE XX1080 $45.00 (For use in infrared sight experiment systems) Come and see. Showroom: 51 Georges Crescent, Georges Hall, NSW 2198 (Behind Caltex Service Station In Birdwood Road) one 724 6982 TRADING HOURS: Monday to Friday 9.00 a.m. to 4.00 p.m. Saturday from 9.00 a.m. to 12.00 noon. JUN E 1989 75