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Build the NUMBER CRUNCHER What can you do with 10 ICs, three LEDs, two displays and a power supply? You can build the Number Cruncher! It chooses a 2-digit number between O and 99, and you have to guess what it is. By GREIG SHERIDAN & DARREN YATES Think of a number between 0 and 99, double it, add 10, take away the number you first though of, divide it by 10 and what do you get? Well, this project isn't quite that clever but it does automatically select a 2-digit number between 1 and 99, stores it away, and then lets you try to guess what it is. Each time you make a guess, it tells you whether your guess is too high or too low. You then make repeated attempts, all the time zeroing in until you finally guess the correct number. So what's the purpose behind it? Well, to be strictly honest, there is no purpose except to teach and entertain! By building the Number Cruncher, you'll learn a good deal about digital electronics and how logic circuits work. And, when you've finished, you'll have a useful game that will entertain the family for hours. There are just three pushbutton switch controls on the Number Cruncher and these are arranged in a row along the bottom of the PC board. The first (bottom left) increments the TENS digit of a 2-digit LED display, while the second increments the UNITS digit. The third pushbutton switch (on the right) is designated MOVE and has a number of functions. When you first apply power, the display is blank and the game defaults to the reset mode. During this time, two "hidden number" counters are clocked by a lOkHz oscillator. These counters form a random number generator which rapidly cycles between 0 and 99. The game progresses to the running mode when you press the MOVE switch. This latches in a random number and illuminates the 7-segment displays with an initial value of 00. You now try to guess the number by incrementing the display using the TENS and UNITS buttons, and then entering the chosen number by pressing the MOVE button again. To the left of the 2-digit display are three LED indicators. These are the result LEDs. If the number you entered is too low, the bottom red LED glows, Similarly, if it is too high, the top red LED glows. You then enter a new number and press the MOVE button again. When you guess the correct number, the centre green LED glows and the game can be restarted by pressing the MOVE button once more. Block diagram Fig.1 shows the block diagram of the Number Cruncher. The clock (IClOa) provides a square-wave with a frequency of about l0kHz. This is used to clock two decade counters (IC5a & IC5b) to provide the random 2-digit number. The counters are stopped when the 44 SILICON CHIP MOVE button is pressed. Two other BCD (binary coded decimal) counters (IC2a & IC2b) are then clocked by the UNITS and TENS switches. Pressing each switch once increments its associated counter. The outputs from these two counters, along with the outputs from the random number counters, are fed into two 4-bit BCD comparators (IC6 & IC7). These two ICs are really the main stars of the project. They compare the values in the two sets of counters and generate an appropriate output, depending on which is higher and which is lower, or whether they are equal. For example, IC6 compares the values from units counters IC2a and IC5a. Similarly, IC7 compares the values from IC2b and IC5b. The outputs from the comparators are then fed into latch IC8 which is clocked whenever the MOVE switch is pressed. The outputs from this latch then feed the LED drivers to indicate "too high", "too low" and "equal". To show you the number you've pressed, the outputs of IC2a and IC2b are fed into two BCD to 7-segment display drivers (IC3 & IC4). These in turn drive two 7-segment displays. Circuit diagram Let's now take a look at the full circuit diagram - see Fig.2. When power is initially applied, an RC network on pin 9 of IClb sets the flipflop so that its Q output (pin 15) is high. This means that the K input (pin 11) will also be high, while Q-bar (pin 14) will initially be low. This blanks the two 7-segment displays by pulling pin 4 of the two 7-segment display drivers (IC3 & IC4) low. The initial high on IClb's Q output does several things. First, it resets the two guess counters, IC2a & IC2b, so that they don't come on with some random number. Second, it resets quad latch stage IC8 and this in turn ensures that LEDs 1-3 are initially extinguished. And third, it enables the two cascaded random number counters which immediately begin counting clock pulses from IClOa. IClOa is part of a 4093 quad NAND Schmitt trigger IC and is configured here as a square-wave oscillator. It oscillates at a frequency of about l0kHz, as set by the .0lµF capacitor and the 8.2kQ feedback resistor. Its output (pin 11) clocks IC5 which INCREMENT UNITS S1 T UNITS I ~ l7 DISPLAY DRIVER IC3 RANDOM COUNTER TOO HIGH UNITS COMPARATOR IC& ICSa CLOCK l 1 LED EQUALS LED LATCH IC8 IC10a RANDOM COUNTER IC5b TENS COMPARATOR IC7 TOO LOW LED INCREMENT TENS S2 TENS T I ~ COUNTER I -_ _.....,__ ___,_ IC2b w:rvtt: IC4 l7 l 1 Fig.1: block diagram of the Number Cruncher. When the MOVE button is pressed, the two random number counters are stopped. The user then tries to guess the hidden number by incrementing counters IC2a & IC2b until the desired number appears on the 7-segment LED displays. The entered number is then compared with the hidden number using IC7 & IC8. is one-half of a 4518 dual BCD UP counter. Thl:l Q4 output from IC5a in turn clocks IC5b, thereby producing a 2-digit UP counter which continuously cycles from 0 to 99. The outputs of counters IC5a & IC5b are fed into the "B" inputs ofIC6 and IC7. These two ICs are CMOS 4585 4bit comparators and it's these devices that tell us whether the input number is too high, too low, or "just right". Debounce switches ICla is one half of a 4027 dual JK flipflop and is used to debounce the MOVE switch (S3). Each time S3 is pressed, it releases the reset on pin 4 and pulls the set input (pin 7) high. PARTS LIST 1 PC board, code SC08110921, 195 x 97mm 4 10mm rubber feet 3 PC-mount piano key switches 1 metre tinned copper wire (for links) 3 BC547 NPN transistors (01 -03) 1 1N4004 silicon diode (D1) 3 1N914 signal diodes (02-04) 2 5mm red LEDs (LED1 ,LED3) 1 5mm green LED (LED2) 2 LTS543 or equivalent commoncathode ?-segment displays Semiconductors 2 4027 dual JK flipflops (IC1 ,IC9) 2 4518 dual 4-bit up counters (IC2,IC5) 2 4511 ?-segment decoders (IC3,IC4) 2 4585 4-bit magnitude comparators (IC6,IC7) 1 40175 quad D latch (IC8) 1 4093 quad Schmitt trigger 2-input NANO gate (IC10) Capacitors 1 100µF 16VW electrolytic 1 0.1 µF 63VW MKT polyester 1 .01 µF 63VW MKT polyester Resistors (0.25W, 1%) 8100kQ 310kn 1 8.2kQ 171kQ DECEMBER 1992 45 01 1N4004 INCREMENT UNITS S1 I ~ 100k 5 3 J IC9b 0 r ~ - 116 10 112 . 11& T I I EN Q ~ lo Q3 R 04 LT 7 l 12 Q2 IC21 4518 1a 3 11 01 CK u ~K477 13 i ( 2 14 I I 6 6 11 4 d 10 2 C 4511 , 9 •I 1,. -!! • 14 ~ ~ P,~k l +V IC10:_l 4093 14 13 '-)1 :ill s 9 _r K 11 01 11 Q2 12 IC51 .~ RANDOM NUMBER CLOCK .8· d 10 BI -!! 41! ,_ 14 04 14 EN 7 10 i1!.. A4 A3 A2 Al INL 9 82 1 03 13 4518 2 1 IC& . 8- >L 4515 OUT 3 D -!-5 I~ < IN 8 OUT ~2 ~ +V 1~:14~ -- - ~ 16 R -- 0.1 11 81 9 82 035 1 83 • 1A . IC7 4515 OUT . • 01 - OUT 12 12 1 :i ... ~ r' s 1 s iiJ D3 I ~ ' 1N914 R ~ ...] R 17 12 EN cm Q 1 £HK!~ 100k B ~ • '-:!I 100k E~C VIEWED FROM BELOW _J! 1 01 3 Q2 4 Q3 5 I 1a I i . . I I 1 B . I 2 C Q4 6 CK ' I 7 A +V 4 13 BI a 13 4511 DEBOUNCE ..I! .!§ 711k 7 b 12 6 11 4 C IC4 8 D ~ NUMBER CRUNCHER SILICON CHIP 2 C: 14 ~ E ~ 04 I I 100k CLK 9 -:I '-,,Cl B O 15 13 CK IC1b 11 K .r8 6 10k K(:.\A I DEBOUNCE -- 1~. C re J R INCREMENT TENS -!' LED3 TOO LOW IC1®~1 ~ 17 100k E ~ 3 ~ ~01 Q3 10 ..,. CLR rf:\A 01 41175 03 A1 A2 A3 A4 10 7 2 15 K '-C,,I' C A mLr- I 14 16 R 11111 Q3 BC547 t-,fMffE 100k 1k Q2 BC547 , ICI I■100k POWER UP RESET LED2 EQUAL E 84 -!! -1: +V 01 3 024 04 '-.!:l7 B ~ I IC5ll EN 10K Q4 15 13 D4 K /'F\A C OUT ~> N 1 CLK ........1 IN > 13 IN 1k Q1 BC547 18 5 < 6 LED1 TOO HIGH f, +V 46 UNITS +V ~5 16 1T .01I i 100 1&VW! IIIIPIAY1 D •• LfJ 7 12 ' IC3 711k 13 I 1 DEBDUNCE 100k Cl 17:\ _ .1 \!:I - +9-1 2V +V d 1• 2 • 9 1 I 15 9 I 14 18 DISPIAY2 Tall .8 d -!! ~K The result is a clean positive-going Now the really tricky 9V pulse on ICla's Q output (pin 1). work is done inside these Thus, when S3 is pressed to start two ICs. Let's see how it all the game, ICla's Q output goes high works. Since we want to guess a and clocks flipflop IClb. This resets IClb which now switches its Q-bar number between 0 and 99, output high and this enables the dis- we ne~d eight bits·to hold play drivers, so that the displays now that number; ie, four bits show "00". At the same time, IClb's Q {or the "units" and four bits output switches low and this releases for the "tens" . the resets on the guess counters, IC2a IC6 compares the lower & IC2b. The enable inputs of IC5a & four bits from IC2a with IC5b are also pulled low and so these those from IC5a (ie, the counters are latched, thus locking in units). The outputs at pins 2, 12 & 13 then indicate the the random number. IC9 is a 4027 dual JK flipflop and results of this comparison. this is used to debounce switches Sl If the units number entered and S2. The resulting pulses from IC9a in (ie, the number on the and IC9b form the clock signals for "A" inputs) is higher than IC2a and IC2b. These counters corre- the random number on the spond to those shown in Fig.1 and are "B" inputs, pin 13 goes used to hold the entered number. Each high. Conversely, if "A" is less press of the appropriate switch applies a single clock pulse to either pin than "B", then pin 12 goes 1 or to pin 9 to increment either the high. And if they are equal, pin 3 goes high. Note that tens or units digits. The 4-bit (Ql-Q4) outputs from each only one of these three outcounter are fed to 4511 7-segment de- puts can be high at any coder/ driver ICs (IC3 & IC4). These time. then drive two 7-segment displays to The latter two outputs indicate the number that's being en- (pins 3 & 12) are coupled to tered. At the same time, the positive- the cascading inputs of the going pulse that results each time an "tens" comparator, IC7, but increment switch is pressed is ap- note that pin 13 of IC6 is plied to diode OR gate D3 & D4. The left disconnected. By dooutput of this OR gate is inverted by • ing this, IC7 is able to disIClOb and resets latch IC8 to extin- tinguish between numbers INCREMENT MOVE guish any result LED (LEDl - LED3) of the same decade. UNITS that may be on from a previous guess. IC7 is also used to compare the outputs of IC2b Fig.3: install the parts on the PC board exactly 8-bit comparator as shown here & note that all the ICs face in the and IC5b. Its three outputs same direction. As well as driving the 7-segment at pins 3, 12 & 13 then give decoders, the outputs ofIC2a and IC2b the result of the overall are also fed into the "A" inputs ofIC6 comparison between the two num- age to set and reset them and do not and IC7 respectively. These two de- bers. Pin 12 goes high if the guess is respond when the switch wipers are vices are 4585 4-bit comparators and too low; pin 13 goes high if the guess held low. The high on pin 2 of IC8 is also fed have been cascaded to form an 8-bit is too high; and pin 3 goes high if the to the J input (pin 10) of IClb. Thus , BCD comparator by tying the cascad- guess is correct. These outputs are fed into IC8, a IClb now has a "high" on its J input ing inputs (pins 4, 5 & 6) appropri40175 quad D latch which is clocked and a "low" on its K input. When the ately high or low. each time the MOVE switch (S3) is MOVE switch is again depressed, the pressed. If the number entered is too resulting clock pulse from IC la causes high, pin 15 of IC8 goes high and IClb to set, sending its Q output (pin turns on LED 1 via transistor Ql. If 15) high and its Q-bar output (pin 14) the number is too low, pin 10 goes low. This causes the displays to blank Fig.2 (left): the two 4-bit magnitude high and lights LED 3 via Q3. again and the game can now be recomparators, IC7 & ICB, form the If the number entered is correct, started by pressing the MOVE button heart of the circuit. These compare pin 2 of IC8 (Ql) goes high and lights once more. the number entered into IC2a & IC2b LED 2. At the same time, Ql-bar (pin with the hidden number in counters 3) goes low and this disables the twq Construction IC5a & IC5b and generate an INCREMENT switches. This occurs beAll of the components for the appropriate output to ·drive quad D cause the switch debounce flipflops Number Cruncher are mounted on a latch ICB. IC8 then drives the (IC9a & IC9b) require a positive volt- PC board coded SC08110921 and indicator LEDs via transistors Qt-Q3. DECEMBER 1992 47 Tt SC08110921 ol codes check the values with your DMM. Note that Dl must be a 1N4004 while D2-D4 are all 1N914s. The two capacitors can be soldered in next, followed by the 't ransistors and the ICs. Be sure to install the correct IC at each location and note that they are all oriented in the same direction. A clean, fine-tipped soldering iron is essential for this job, since many of the tracks run quite close to the IC pins. Don't use a soldering iron that's too big for this job. If you do, you risk damage to the tracks and you will probably wind up with lots of short circuits. Finally, install the LEDs, 7-segment displays and the three switches. Note that the green LED is LED 2 (centre) and check that all the LEDs are correctly oriented (the anode lead is the longer of the two). The 7-segment displays must be installed with their decimal points at bottom right. Switching on lV)o o-fiTI=o;.=~~ a a ~ Fig.4: check your PC board for defects by comparing it to this full-size pattern before installing any of the parts. measuring 195 x 98mm. Fig.3 shows the assembly details. Before actually installing any of the parts, it's a good idea to check the board carefully for etching defects. Repair any defects that you do find, then start the assembly by installing the wire links. It's important to keep these wire 48 SILICON CHIP links as straight as possible, to avoid shorts. If necessary, you can straighten the link wire by clamping one end in a vyce and then stretching it slightly by pulling the other end with a pair or pliers. Once all the links are in, you can install the resistors and the diodes. If you don't know the resistor colour Now for the smoke test but first check your completed board carefully against Fig.3 to ensure that all parts are correct. Everything OK? If so, connect your DMM (set to the mA range) in series with a 9V plugpack supply and apply power to the board. Note: do not use a 12V plugpack supply, as its output may be well in excess of the maximum 15V supply voltage for the CMOS ICs. Initially, none of the displays or LEDs should be on and the current should be less than 5mA (typically about ZmA) . If the current exceeds 5mA, switch off immediately and check for wiring errors. An IC might have been mounted the wrong way around or there could be a short on the copper side of the PC board. If everything checks out so far, press the MOVE button (S3) and check that the display now shows "00". At the same time, the current reading should jump to about 100mA. Now press the INCREMENT buttons (S1 & S2) until the nµmber you want to enter is dis. played and then press the MOVE button (S3). Finally, check that one of the three indicator LEDs lights to indicate whether you're too high, too low or bang on. Do you know anyone who claims to have ESP? You can now put them to the test. SC