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Build Your Team A Professional Sports Scorebo 14  Silicon Chip siliconchip.com.au Pt.1: By JIM ROWE oard Here’s a build-it-yourself electronic scoreboard that you can put together for a tiny fraction of what you’d have to pay for a commercial scoreboard. It offers large, easy-to-read displays, a convenient wireless console and modular construction which makes it especially easy for a group of people to build. It’s mainly designed for basketball but can be used for other games as well. C OMMERCIALLY AVAILABLE bas- ketball scoreboards have price tags starting at about $2500 and zooming upwards into the stratosphere if you want features like a wireless control console. That means they’re generally out of the question for amateur and school sports teams with plenty of enthusiasm but almost no budget. If you’re in that position, what would you say to a scoreboard you can build yourself for a fraction of the cost of a commercial model? Not only that but it boasts features like big, bright digits 130mm high and a wireless console that can be up to 50 metres or so from the scoreboard itself. It also offers modular construction, so it can be built up easily by a group of siliconchip.com.au people – as long as they have a modest amount of experience assembling electronic projects and some basic woodworking skills. Sounds like a pretty good project for school technology classes, doesn’t it? Especially if the school has some keen basketballers but very little money to spend on luxury facilities like a scoreboard. As you can see from the features box and the photos, the scoreboard offers most of the features found on the majority of commercial units. It has a 2.5-digit display for each team’s score, able to show scores up to 199. It also has a single digit display for the current game period, able to show 1/2/3/4 or an “E” for extra time. And finally, March 2005  15 16  Silicon Chip siliconchip.com.au Fig.1: the Control Console circuit is based on a PIC16F84A-04 microcontroller and a 2.4GHz transmitter module. The PIC scans the control key switches and generates the corresponding command codes which are then transmitted to a receiver in the Scoreboard. there’s the 4-digit countdown timer display, which shows the remaining time in the current period in minutes and seconds for all except the last minute, when it automatically swings over to showing seconds and tenths of a second. A colon is displayed between the minutes and seconds, while a single “decimal point” appears during the final minute – so it’s always easy to see which mode it’s in. The countdown timer automatically resets at the start of each new game period, when you press the “Start Next Game Period” button on the console. The Period display also changes automatically when this button is pressed. Similarly, the timer stops when you press the “Time Out” button and restarts again (from where it stopped) when you press the “Time In” button. To allow easy updating of the score for each team, the console has separate +3, +2 and +1 buttons for them both. It also provides -1 buttons for both teams, so their scores can be decremented easily in the event of scoring disputes or penalties. How do you reset the Scoreboard for the start of a new game? Simply by pressing the two Reset buttons on the console, at the same time. However, to reduce the risk of anyone doing this accidentally in the middle of a game (which would have disastrous consequences), all that happens the first time you press these buttons is that the console flashes a LED on its own front panel marked “Confirm Reset”. It only sends the actual reset command to the scoreboard if you then respond by again pressing the two buttons. Otherwise the reset command will be ignored. The circuitry for the scoreboard itself is built on five PC boards: four for the various display modules and the remaining board for the controller that runs it all. These boards are all mounted in a timber frame, designed to be hung up on a wall, with a 26-way ribbon cable linking all of the boards and providing the displays with power and display data. The control console circuitry is built on two somewhat smaller PC boards, which are mounted in a compact plastic case. The data link between the console and the scoreboard is via 2.4GHz microwave radio signals. By the way, this Scoreboard project has been developed in conjunction siliconchip.com.au Electronic Scoreboard: Main Features • Four separate displays for Home and Away team scores (0-199), current game period (1-2-3-4-E) and the period countdown timer. • Display digits are all 130mm high and are formed using high-brightness 10mm LEDs (four per digit segment). The team score displays are in green, the current period in orange and the timer displays in red for easy reading. • The period countdown timer display shows minutes and seconds during most of each game period but automatically changes over to seconds and 1/10 seconds during the last minute of play. The end of each game period is also signalled by a brief burst of sound from a piezo siren. • All scoreboard functions are controlled by a small wireless console which can be located at almost any convenient location inside the court. • Console buttons allow easy addition of 3, 2 or 1 points to the score of either team, along with the ability to subtract 1 from either team’s score in the event of penalties and scoring disputes. There • Console features extra buttons to start the next game period, stop the countdown timer (Time Out) or restart it again (Time In) – plus a pair of buttons which must be pressed together to reset the scoreboard for a new game. This last pair of buttons must be pressed together twice, to confirm that you really do want to reset the board (which should prevent you accidentally wiping the scores and timers clean. • Unit can be set up to play according to either NBA, FIBA (International) or NCAA basketball rules. This is done by setting DIP switches inside the console. • Both the scoreboard and the control console operate from 12V DC – eg, from either 12V plug pack supplies or 12V batteries. There are no dangerous voltages anywhere inside. This also means they can be used in areas where there is no mains power. with Jaycar Electronics, which holds the design copyright for both its hardware and firmware. As a result, kits for the project will only be available from Jaycar stores. OK, so that’s a quick rundown on what the new scoreboard does and how it’s used. Now let’s look at how it works. Console operation Like the scoreboard itself, the control console is based on a preprogrammed low-cost PIC16F84A microcontroller – see Fig.1. In the case of the console, the PIC operates at a clock frequency of 4MHz, giving a machine cycle of 1ms. The main functions performed by the PIC in the console are scanning the control key switches and generating the corresponding command codes for the scoreboard. As you can see from the circuit, the keys are connected in a matrix configuration to seven of the PIC’s Port B I/O pins, with the three main rows connected to pins RB5-RB7 (configured as outputs) and the four columns connected to pins RB0-RB3 (configured as inputs). The scoreboard command codes generated by the PIC in response to the various buttons being pressed are fed out via Port A I/O pin RA0, configured here as an output. The two Reset buttons are connected in series so that both must be pressed simultaneously, in order to link RB7 and RB0. When this event is sensed by the PIC, it first places a logic high on I/O pin RA4, also configured here as an output. This turns on transistor Q7 which then turns on LED2 – the “Confirm Reset” LED. If you subsequently press the two Reset buttons again, the PIC turns off Q7 and LED2, generates the scoreboard reset command code and sends it out via pin RA0. If, on the other hand, you’ve made a mistake in pressing the Reset buttons and don’t press them again – but press some other button instead – the PIC merely turns off Q7 and LED2 and sends the command March 2005  17 18  Silicon Chip siliconchip.com.au Fig.2: the coded signals from the transmitter are picked up by the receiver in the Scoreboard Controller, decoded and fed to the RB0 input of PIC microcontroller IC1 (PIC16F84A-20P). The microcontroller then sequentially drives the displays via IC2, IC3 and power Mosfets Q2-Q8. code corresponding to the newly pressed button. Another function performed by the PIC is checking the DIP switches (S2) used to set which basketball code you want the scoreboard to use: FIBA, NBA or NCAA. As you can see, the DIP switches are connected to I/O pins RA1-RA3, configured as inputs. All three pins are also connected to ground via 10kW pulldown resistors, so that only the pin corresponding to the switch that is “on” will be taken to logic high level (+5V). Note that the PIC is programmed to check the status of the S2 DIP switches only when it first powers up. That’s because the DIP switches are inside the console and can’t be changed without turning it off and opening the case (changing the rules is not something you’d want to do during a game, anyway). So these switches are only scanned during the console’s power-up sequence and the appropriate control code sent to the scoreboard then. The rest of the console circuitry is used to process the control codes generated by the PIC and sent out via pin RA0, so they can be transmitted to the scoreboard via the AWM609TX data transmitter module. This operates on one of four frequency channels in the range 2.40 - 2.483GHz, as selected by the four DIP switches marked S1. The AWM609TX module and its matching AWM608RX receiver module (as used in the scoreboard itself) were originally designed for transmitting video and stereo audio signals, using frequency modulation and demodulation for both the video and audio. We use all three signal channels here to transmit our digital scoreboard control codes by using the circuitry around IC2, IC3 and transistors Q1-Q4 to pre-encode the digital codes into audio tones, using a simple synchronous phase-shift keying (SPSK) system. This works as follows. First, clock oscillator IC2b generates a continuous square wave clock signal of approximately 10kHz. This is then fed to flipflop IC3b, which toggles back and forth to produce two 5kHz square wave signals at its Q and Q-bar outputs – locked in phase but of opposite polarity. Then one of these 5kHz signals is fed to the clock input of flipflop IC3a, which produces a locked 2.5kHz signal at its Q output. siliconchip.com.au Here is a sneak preview of the main PC board inside the Control Console. The assembly details will be published next month. The 2.5kHz signal from IC3a is then fed through buffer transistors Q1 and Q2, and fed to the video input of the AWM609TX transmitter module. This then sends it to the scoreboard, where it’s used as the clock signal for the SPSK demodulator. On the other hand, the two locked complementary 5kHz signals from IC3b are fed to gates IC2c and IC2a, where they are effectively used to encode the digital control code signals from pin RA0 of IC1. IC2d is used to produce an inverted version of the digital signals and this is fed to IC2c together with one 5kHz signal. The uninverted digital signals are fed to IC2a, along with the other 5kHz signal. As a result, when the digital signal from IC1 is high (1), the 5kHz signal from pin 8 of IC3 is gated through IC2a. Conversely, when the digital signal is low (0), the opposite polarity 5kHz signal from pin 9 of IC3 is gated through IC2c instead. Since the outputs from IC2a and IC2c are effectively combined via diodes D2 and D3, this means that although a 5kHz square wave signal always appears at the anodes of the two diodes, the signal’s polarity or phase at any instant depends on the digital logic level coming from IC1. In other words, the digital control codes are encoded on this 5kHz square wave signal as SPSK modulation. To ensure reliable transmission of this SPSK signal, we feed it through transistors Q3 and Q4 which act as complementary buffers. This produces two versions of the same 5kHz signal with opposite polarity, which are then fed to the two audio signal inputs of the AWM609TX transmitter module. As a result, we not only make use of all three signal channels of the AWM609TX but also achieve maximum link redundancy and noise rejection. But what’s the purpose of the circuitry around transistors Q5, Q6, diode D4 and LED1? These provide a poweron indicator for the console – but a power indicator with a difference. Because the base of Q5 is fed with the buffered 2.5kHz clock signal from Q1, it therefore switches on and off with this signal. The resulting 2.5kHz signal at its collector is fed to the base of Q6 through a simple rectifier/ clamp circuit using the 220nF capacitor, D4 and the 100kW resistor, so Q6 is only turned on during the positive half-cycles of the 2.5kHz signal. As a result, when LED1 glows, it indicates not only that power is applied to the console circuitry as a whole but also that the 2.5kHz signal from IC3a is present – and hence that oscillator IC2b and flipflop IC3b are working. Scoreboard controller Fig.2 shows the circuit details for the Scoreboard Display Controller. March 2005  19 Fig.3: the Scoreboard Display 1 (or Period) board is driven by the control board and uses 28 10mm yellow LEDs to form a single digit. Once again, all functions are under the control of a PIC16F84A microcontroller, which in this case runs at a clock speed of 10MHz (giving a machine cycle time of 400ns). This PIC responds to the control codes from the console, keeps the 20  Silicon Chip scores for the two teams, runs the countdown timer and looks after displaying all of the information via the display board modules. It also handles the important job of sounding the piezo siren briefly at the end of each game period. The control codes from the console arrive at the controller board via the AWM608RX receiver module. This module can operate on any one of four 2.4GHz channels like the transmitter module, as selected by the Channel Select DIP switches (S1). Naturally, the receiver must be set to work on the same frequency channel as the transmitter module, for correct operation of the data link. All of the scoreboard controller circuitry around transistors Q9-Q11, IC4 and IC5 is used in decoding the output signals from the AWM608RX receiver module, to reconstruct the digital control codes sent from the console. These are then fed to the PIC via its RB0 input pin. The decoding is more or less the reverse of the SPSK encoding procedure used in the console. When the 2.5kHz decoding clock signal emerges from the video output of the receiver module, it is first squared up by passing it through a clamp and buffer circuit using diode D4 and transistor Q11. It’s then passed through gate IC4b, used here as a noninverting buffer. From IC4b, it is then fed to the clock inputs of flipflops IC5b and IC5a and also to the base of transistor Q12 via a 10kW resistor. This causes Q12 to conduct during the positive half cycles of the 2.5kHz signal, drawing current through LED1 and making it glow. This allows LED1 to function as a “Carrier Present” indicator. The two complementary 5kHz signals containing the SPSK information from the console emerge from the stereo audio outputs (Ro and Lo) of the receiver module. They are then fed through clamp and buffer circuits similar to those used for the 2.5kHz signal. In this case, one signal is passed through Q10 and IC4a, while the other passes through Q9 and IC4d. One is then fed to the D (data) input of IC5b, while the other is fed to the corresponding input of IC5a. So the two 5kHz data signals are fed to the data inputs of the flipflops, while the phase-locked 2.5kHz clock signal is fed to their clock inputs. This means that on each low-to-high transition of the 2.5kHz signal, the logic level of the two 5kHz signals will be clocked into the flipflops. And as the two signals are the complement of each other, this means that one flipflop should be driven into the set state (Q output siliconchip.com.au Fig.4: the Scoreboard Display 3 board (for Home/Away scores) uses 67 10mm green LEDs to form two complete 7-segment digits and a leading “1” digit. There are two of these boards, each showing a maximum score of 199. high) when the other is driven into the reset state (Q output low). As a result, they toggle back and forth in complementary fashion, in time with the digital control code information coming from the console. siliconchip.com.au To complete this decoding, we feed the Q-bar output of IC5b and the Q output of IC5a to AND gate IC4c, which therefore provides an output high only when both of these complementary flipflop outputs are high simultane- ously. The output of IC4b therefore delivers a clean reconstruction of the original digital control code sent by the console PIC, with a high level of reliability and noise rejection. This decoded control code signal is made March 2005  21 22  Silicon Chip siliconchip.com.au Fig.5: the Scoreboard Display 4 board carries the LEDs and switching transistors for the countdown timer. It has four 7-segment digits plus a colon and these are made up using 120 10mm red LEDs. Five separate PC boards make up the main display panel: a receiver/controller board, one period display board (yellow LEDs), two score display boards (green LEDs) and one countdown timer board (red LEDs). We show you how to build them next month. available at test point TP1 as well as being fed to the RB0 input of IC1. Inside IC1, the PIC’s firmware program responds to the control codes to perform all of the functions in controlling the scoreboard – updating the team scores, operating the countdown timer and keeping the various displays operating. There are 12 display digits in all: three for each team score display, one for the current period display and five for the countdown timer – although the centre digit of the timer display module is dedicated to displaying only a colon or a decimal point. All of the displays are based on the standard 7-segment digit format but use discrete highoutput LEDs rather than dedicated 7-segment display devices. We do this using four seriesconnected 10mm LEDs in each digit segment, in order to get large 130mm high digits. Display multiplexing The 12 displays are all driven sequentially by the PIC controller in standard multiplexed fashion, with one complete display cycle taking place every 25ms. This means that the displays are refreshed 40 times each siliconchip.com.au second (except for very short breaks when the PIC is processing command codes from the console). To turn on each display digit, the PIC outputs a digit code via pins RA0-RA3. This information is decoded by transistor Q1 and by IC2 & IC3, which then feed a logic high to the appropriate digit display circuit via the corresponding line of 26-way cable connector CON1. At the same time, the PIC makes the current 7-segment display code for that digit available via output pins RB1-RB7. These outputs are used to drive power MOSFETs Q2-Q8, which are the power switches for the display segment control lines of all the displays. So as each display is turned on, the appropriate segments are also switched on to display the correct digit or other character. The only remaining function performed by IC1 is to turn on a piezo siren briefly at the end of each game period. It does this by allowing its RA4 output pin (an open collector output) to be pulled high by the 10kW resistor, for three seconds at the end of each game period. This logic high is used to turn on power MOSFET Q13, which in turn switches on a piezo alarm connected to CON3. All the scoreboard controller’s circuitry operates from +5V, derived from the +12V input by regulator REG1. Although the PIC micro and the rest of the CMOS circuitry draw very little current, the AWM608RX data receiver draws over 200mA – bringing the total drain from the +5V rail to nearly 250mA. To allow the regulator to cope with this, diodes D2 and D3 are used to reduce its input voltage, while the regulator is also fitted with a heatsink to help it dissipate the remaining 1.5W of power without overheating. The display modules As mentioned earlier, all the scoreboard displays are on separate boards, which connect to the controller board in daisy chain fashion via a 26-way ribbon cable. This connects to CON1 on the controller board and delivers +12V to the display boards, along with their digit and segment drive signals. All the displays use the same basic circuitry, the operation of which can be understood quite easily by looking at the circuit for the single digit “Period” display (Scoreboard Display 1) – see Fig.3. The digit drive signal from the conMarch 2005  23 Par t s Lis t – Sports Scoreboard 1 900 x 600mm sheet of 12mm plywood 2 900mm lengths of 30 x 15mm DAR maple wood 2 570mm lengths of 30 x 15mm DAR maple wood 5 26-way IDC line sockets (Jaycar PS-0987) 1 piezo alarm, 12V (Jaycar LA5256) 1 1600mm length of 26-way IDC ribbon cable 2 16-way IDC line sockets (Jaycar PS-0985) 1 70mm length of 16-way IDC ribbon cable 1 12V 1A DC plugpack (Jaycar MP-3137) 1 12V 300mA DC plugpack (Jaycar MP-3011) 2 31mm lengths of 1mm diameter brass wire Woodworking glue, 25mm long 1.5mm diameter nails, etc. Main Controller Board (x1) 1 PC board, code BSBCONTR, 127 x 190mm 1 Airwave AWM608RX 2.4GHz receiver module (Jaycar QC-3592) 1 TO-220 heatsink, 6021 type 30 x 25 x 13mm (Jaycar HH-8504) 1 4-way DIP switch (S1) 1 10MHz crystal (X1) 1 PC-mount 26-way DIL socket (CON1) 1 PC-mount 2.5mm concentric DC socket (CON2) 1 2-way PC-mount terminal block (CON3) 4 25mm x M3 tapped metal spacers 13 6mm x M3 machine screws, round head 4 15mm x M3 machine screws, csk head 9 M3 nuts and star lockwashers Semiconductors 1 PIC16F84A-20P microcontroller programmed with SCORDISP. HEX (IC1) 2 4028B CMOS decoders (IC2,IC3) 1 74HC08 quad AND gate (IC4) 1 74HC74 dual D-type flipflop (IC5) 4 PN100 NPN transistors (Q1,Q9, Q10,Q12) 24  Silicon Chip 8 MTP3055 power MOSFETs (Q2Q8,Q13) 1 PN200 PNP transistor (Q11) 1 7805 +5V regulator (REG1) 1 5mm red LED (LED1) 3 1N4004 1A diode (D1-D3) 3 1N4148 signal diode (D4-D7) Capacitors 1 2200mF 16V RB electrolytic 1 100mF 16V RB electrolytic 1 10mF 16V tantalum 3 4.7mF 16V tantalum 5 100nF multilayer monolithic 1 100nF MKT metallised polyester 2 33pF NPO disc ceramic Resistors (0.25W 1%) 1 100kW 1 4.7kW 2 47kW 1 470W 1 22kW 8 47W 6 10kW 7 10W Period Display Board (x1) 1 PC board, code BSB-D1, 102 x 190mm 1 PC-mount 26-way DIL socket (CON1) 4 25mm x M3 tapped metal spacers 5 6mm x M3 machine screws, round head 4 15mm x M3 machine screws, csk head 1 M3 nut & star lockwasher Semiconductors 1 PN100 NPN transistor (Q1) 1 BD136 PNP transistor (Q2) 28 yellow 10mm LEDs, high brightness or standard Capacitors 1 1000mF 16V RB electrolytic Resistors (0.25W 1%) 2 4.7kW 1 120W Team Score Display Boards (x2) 1 PC board, code BSB-D3, 218 x 190mm 1 PC-mount 26-way DIL socket (CON1) 6 25mm x M3 tappers metal spacers 9 6mm x M3 machine screws, round head 6 15mm x M3 machine screws, csk head 3 M3 nuts & star lockwashers Semiconductors 3 PN100 NPN transistors (Q1,Q2,Q3) 3 BD136 PNP transistors (Q4,Q5,Q6) 67 green 10mm LEDs, high brightness or standard Capacitors 1 1000mF 16V RB electrolytic Resistors (0.25W 1%) 6 4.7kW 1 22W 3 120W Timer Display Board (x1) 1 PC board, code BSB-D4, 380 x 190mm 1 PC-mount 26-way DIL socket (CON1) 6 25mm x M3 tapped metal spacers 11 6mm x M3 machine screws, round head 6 15mm x M3 machine screws, csk head 5 M3 nuts & star lockwashers Semiconductors 5 PN100 NPN transistors (Q1-Q5) 5 BD136 PNP transistors (Q6-Q10) 120 red 10mm LEDs, highbrightness or standard Capacitors 2 1000mF 16V RB electrolytic 1 4.7nF 50V greencap Resistors (0.25W 1%) 10 4.7kW 5 120W Control Console 1 console case, 189 x 134 x 32/55mm (Jaycar HB-6094) 1 PC board, code BSBKYBD1, 178 x 111mm 1 PC board, code BSBKYBD2, 163 x 100mm 1 Airwave AWM609TX 2.4GHz transmitter module (Jaycar QC3590) 1 TO-220 heatsink, 6073B type 19 x 19 x 9.5mm (Jaycar HH-8502) 2 4-way DIP switch (S1, S2) 1 4MHz crystal (X1) siliconchip.com.au 13 PC-mount pushbutton switches, 17.5mm square (2 x red, 2 x yellow, 2 x black, 2 x grey, 3 x white, 1 x green and 1 x blue keytops) 1 2.5mm concentric DC socket (CON1) 1 16-way DIL socket, vertical PCmount (CON2) 1 16-way DIL socket, 90 PC-mount (CON3) 9 4g x 9mm self-tapping screws Semiconductors 1 PIC16F84A-04 microcontroller programmed with SCORKYBD. HEX firmware (IC1) 1 74HC132 quad Schmitt NAND gate (IC2) 1 74HC74 dual D-type flipflop (IC3) 5 PN100 NPN transistors (Q2, Q4-Q7) 2 PN200 PNP transistors (Q1,Q3) 1 7805 +5V regulator (REG1) 1 1N4004 1A diode (D1) 3 1N4148 signal diodes (D2-D4) 1 5mm green LED (LED1) 1 5mm red LED (LED2) Capacitors 1 2200mF 16V RB electrolytic 1 100mF 16V RB electrolytic 1 47mF 16V RB electrolytic 2 470nF MKT metallised polyester 1 220nF MKT metallised polyester 4 100nF multilayer monolithic 1 10nF MKT metallised polyester 2 33pF NPO ceramic Resistors (0.25W 1%) 2 100kW 1 2.2kW 2 22kW 1 470W 15 10kW 1 390W 1 6.8kW 1 180W 4 4.7kW Where To Buy A Kit Jaycar Electronics has sponsored the development of this project and they own the design copyright. A full kit of parts will be available from Jaycar in due course – Cat. KC5408. This kit includes a pre-built wooden display frame with screenprinted lettering and individual Perspex covers for the displays; screen-printed and solder-masked PC boards; all on-board parts; and a control console case with a prepunched front panel and screened lettering. siliconchip.com.au Basketball Rules: The Main Differences RULE Duration of Game Extra Time Duration Timeouts Shot Clock Game Clock Stops After Successful Field Goal FIBA NBA NCAA 4 x 10 min periods 4 x 12 min periods 2 x 20 min halves 5 minutes 5 minutes 5 minutes 1 x 60 sec in each of 6 x 60 sec, 1 x 20 sec 4 x 75 sec, 2 x 30 sec the first 3 periods; 2 x per half per game 60 sec in 4th period 24 seconds 24 seconds 35 seconds Last 2 minutes Last 2 minutes Last minute of 2nd of 4th period & of 4th period & half & last minute extra time extra time of extra time troller board arrives via the appropriate pin on cable connector CON1 – in this case, pin 3. It’s then fed to the base of NPN transistor Q1 via a 4.7kW series resistor, so that Q1 is turned on when the controller takes that digit drive line high. When Q1 turns on, this conducts base current for PNP transistor Q2, which immediately switches on as well. This connects the +12V supply line to the anode ends of all seven display segments, so they’re all potentially able to conduct current and light up. Of course, which segments do actually draw current and light up depends on what happens at their cathode ends, which are each connected to one of the seven segment-drive lines in the 26-way cable, accessible via CON1. So if the controller PIC has turned on only segment control switches Q8, Q6 and Q3, only these three lines will be connected to earth during this digit’s display time and only segments “c”, “b” and “a” will conduct current and light up, to display a “7”. Fig.4 shows the circuit of the Scoreboard Display 3 board. It uses the same basic arrangement for each of its three (strictly 2.5) digits. In fact, the circuit for the two full digits is identical to the Period display, apart from the way their digit drive lines are driven from different pins on CON1 (more about this in a moment). The circuit for the leading “1” digit on this board is very similar too, the main difference being that this display digit is only provided with three segments – ie, segments “b” and “c”, plus three more LEDs which are used to fill in the gaps. These are connected to segment line “d”, via a series 22W resistor to match their current to that of the other segments. Note that each of the three digit drive circuits for this board can be connected to either of two lines on CON1. This is because two versions of the board are used in the Scoreboard, one for the Home team score and the other for the Away team score. So the board used for the Home team display has Q3 driven from pin 4 on CON1, making that digit become D2. Similarly Q2 is driven from pin 6 on CON1 and Q1 from pin 8, so these digits become D3 and D4 respectively. On the other hand, the board used for the Away team score display has Q3, Q2 and Q1 driven from pins 10, 12 and 14 on CON1, so the three digits become D5, D6 and D7. The circuit for Scoreboard Display 4 (the Countdown timer display board), is again very similar – see Fig.5. In fact, the four full digits are wired up in exactly the same manner as the Period display. The only one that’s a little different is the centre “digit” D10, which is used only to display a colon or a decimal point. It only has two sets of four LEDs (one set for each dot) connected, as if they are segments “b” and “c” of that digit. We display a colon by turning on both segments, while turning on segment “c” only produces a decimal point. There is only one other small difference in the circuit for the Countdown timer display, involving the addition of a 4.7nF capacitor between the base and emitter of Q1. This capacitor forms a low-pass filter with the 4.7kW series resistor, filtering out a small amount of multiplexing hash which tends to appear on this digit drive line of the cable. Without this capacitor, digit D12 can glow weakly when it’s not supposed to be glowing at all. Next month That’s all we have space for this month. Next month, we’ll move on to building each of the various modules which make up the Scoreboard. SC March 2005  25