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By JIM ROWE I N THE BAD OLD DAYS, anyone rolling up at a department-store deli to buy a few slices of salami or whatever had to muscle their way through the crowd and try to attract the attention of a salesperson or they’d never get served. It was much the same at employment offices and medical scanning departments, where the rudest and most obnoxious people were often attended to first. Things became more civilised when many of these places brought in systems to ensure that everyone was seen in the order of their arrival. In most cases, these systems use numbered tear-off tickets in a dispenser, plus a LED display or “annunciator” unit which can display the numbers from 00-99 and can be updated to show the next customer to be served. It’s a simple system but it works well. LED annunciators are available commercially but they’re not cheap. So if have been put off by the price tag, this project is for you. You’ll be able to assemble it from a kit for much less than you’d pay for a similar commercial unit. The LED Annunciator has digits 75mm high, each using 28 highbrightness 5mm red LEDs so they’re clearly visible from many metres away. The number displayed – from 00-99 – is incremented simply by pressing a button on the separate small control box which can be located at any convenient place behind a counter or reception desk. The Annunciator has no memory, so Main Features Number Range: 00-99 – incremented by one each time a button on control box is pressed. Built-in piezo buzzer to attract customer attention. Readout: two 75mm-high digits using high-brightness LEDs. Power Supply: 12V DC plugpack (display unit supplied via cable from control box). 62  Silicon Chip when you turn it off and then back on next morning, it comes up with a display of “00” rather than the last ticket number used the day before. However, it’s easy to “run it up” to that number because there’s a built-in self clocking function. You activate this simply by holding down the button for about four seconds and then only releasing it when the display reaches the number you want to start with. The unit also has a built-in piezo buzzer, to produce a short “beep” each time the display is updated, to attract customer attention. However, this can be disabled with a switch if you find it too irritating. The whole thing runs from a lowcost 12V regulated plugpack, although those in rural areas could run it from a 12V battery if they wish. The power feeds into the small control box, which then connects to the display unit via a standard telephone extension cable fitted with RJ12 connectors. Circuit description Fig.1 shows the main circuit. The heart of the display unit is IC2, a siliconchip.com.au Remote LED Annunciator Got a queue situation? Want people to wait their turn as they wait to be served in your vast retail emporium? Maybe you run a hectic fast food store and you want to serve people in their turn. If so, you need this big, bright LED Annunciator. 4553B CMOS 3-decade BCD counter. This device includes latches and output multiplexing, so it performs the counting and also provides the cyclic digit-select and digit data for a multiplexed display. The “active-low” digit-select signals appear on pins 2, 1 & 15, while the BCD digit data appears on pins 9, 7, 6 & 5. We’re only using two digits here, so the pin 15 digit-select output is left unconnected. The other two outputs are used to turn on digit drivers Q8 & Q9 which are BD140 PNP transistors. Since we are using 7-segment displays in the Annunciator, we feed the BCD digit data from IC2 into IC3, a 4511B BCD-to-7-segment converter. This produces the correct 7-segment drive signals for each BCD code fed to it from IC2. The 7-segment signals appear at pins 13, 12, 15, 14, 11, 10 & 9, which are then used to turn on segment driver transistors Q1-Q7. These are low power 2N7000 Mosfets, used here as voltage-controlled switches. The two 7-segment display digits siliconchip.com.au At right is the control box, while on the facing page is the display unit. The two are joined by telephone cable. use four series-connected LEDs for each segment. As you can see, the top anode of each segment is connected to the collector of the digit driver transistor for that digit, so both digits are being used in the common-anode configuration. The cathode connections of each segment in the two digits are connected together, to form the segment drive lines. In turn, these connect to the anodes of switching transistors Q1-Q7, via 150W currentlimiting resistors. As a result, the LEDs in each segment will draw current (about 23mA) whenever the segment driver for that segment is turned on and, at the same time, the digit driver for that digit is also turned on. For example, to display a “2” in the digit 1 position, Q8 is turned on to apply +12V to that digit’s segments, while at the same time segment drivers Q1, Q2, Q4, Q5 & Q7 are also turned on, to allow segments a, b, d, e & g to draw current respectively. All other numerals are displayed in the same way, for both digits. Because the displays are multiplexed in a cyclic fashion at a rate of about 200Hz, they appear to be continuously alight. When power is first applied to the December 2005  63 64  Silicon Chip siliconchip.com.au Fig.1: the display unit is based on IC2, a 4553B CMOS 3-decade BCD counter. It’s clocked (via IC1d and IC1b) each time pushbutton switch S1 in the control box is pressed. Its outputs then drive a 4511B BCD-to-7-segment decoder (IC3), which in turn drives the LED display circuitry via Mosfets Q1-Q7. Conference and Tradeshow Theme: “Meet the Pioneers” & Update your skills Queen Victoria Museum and Art Gallery Precinct - Launceston, Tasmania Australia 2-4th March 2006 Sponsorship opportunities available now Fig.2: there’s not much to the control box circuit – just a couple of switches, a power indicator LED and two resistors. Power comes from a 12V DC plugpack supply. circuit, counter IC2 is reset by the 100nF capacitor and 100kW resistor connected to its MR input (pin 13). This is why the display always starts up with “00”. The count is incremented by feeding pulses from the control box into its pin 12 CLK input. The pulses are generated by pressing pushbutton S1 in the control box (see Fig.2) which in turn connects pin 3 of the RJ12 connectors to the negative supply rail. On the main circuit of Fig.1, pin 3 of the RJ12 connectors is connected to pin 12 of IC1d, which is one section of a 4093B quad CMOS Schmitt NAND gate. The pin 12 input is normally pulled high via a 100kW resistor, which also charges the 100nF capacitor. Since pin 13 of IC1d is connected to +12V as well, this means that both inputs are normally high, so output pin 11 is held low. And because this output is connected to pin 6 of IC1b, this also results in that gate’s pin 4 output being held high. This means that the CLK input of the counter is also held high. GUESS WHO’S COMING TO THE SHOW! Live from Launceston, Tasmania nication satellite commu V DrDish<at>T ldwide TV the unique wor mote channel to pro Come and be a part of the audience and ask the hard questions The conference program will also feature seven of the industries top keynote speakers Ideal program for new comers as well as experienced industry professionals. Make your way to Launceston Download these documents from Conferenceplus.com.au/satellite2006/ Exhibition space on sale now - Hurry it’s selling fast Register your interest to attend • Exhibition Booth Application • Register to attend on-line Event Managers: Conference – Plus PO Box 1144 Legana Tasmania 7277 Phone +61 (3) 6330 1444 Fax + 61 (3) 6330 2190 email info<at>conferenceplus.com.au Pushbutton functions Pushing S1 on the control box pulls pin 12 of IC1d down to ground and discharges the 100nF capacitor. Because this capacitor takes a number of milliseconds to recharge through the 100kW resistor, if S1 is released (or if the contacts bounce), pin 12 of IC1d is pulled low for at least as long as the button is pressed, plus about 10ms. This causes the output of IC1d to switch high for the same period, which results in the output of IC1b switching low as well. This provides a clock pulse for the counter, to increase its count by one. The additional circuitry around diode D1 and gate IC1a (Fig.1) is used to provide the self-incrementing feature, which works as follows. Normally, when pushbutton S1 in the control box is not pressed, the output of IC1d is held low because both its inputs are high. As a result, pin 2 of gate IC1a is also held low, because any charge on the 1mF capacitor is drained away via diode D1. However, when S1 is pressed, as we’ve already seen, this pulls IC1d’s input low and results in its output going high. This allows the 1mF capacitor to begin charging via the 3.3MW resistor. siliconchip.com.au December 2005  65 Now when S1 is pressed only briefly, to simply increment the counter, the 1mF has only begun to charge up when S1 is released again. As a result, the output of IC1d drops low again and any charge on the capacitor is immediately removed by D1. However, if S1 is held down for around four seconds, this results in the output of IC1d being held high for the same time. This allows the 1mF capacitor to fully charge, which in turn allows IC1a to begin working as a relaxation oscillator, at roughly 10Hz. The 10Hz pulses from pin 3 of IC1a are then gated through IC1b to the CLK input of IC2. As soon as the count reaches the number you want, you simply release S1 again and the switch reverts to its normal behaviour. Beep circuit Fig.3: here’s how to install the parts on the display PC board. Make sure all polarised parts, including the LEDs, are correctly oriented. Gate IC1c, diode D2 and transistor Q10 are used to provide the optional “beep” function. Pin 9 of IC1c is coupled to the output of IC1d via a 47nF capacitor. Together with the 2.2MW resistor, this forms a differentiator circuit which delivers a short negative-going pulse to the input of IC1c whenever the output of IC1d falls to logic low level after being high – ie, each time you release pushbutton S1 after pressing it. Diode D2 suppresses the unwanted positive-going pulse when S1 is first pressed. So whenever S1 is released, a short negative-going pulse is applied to the normally-high pin 9 of IC1c which inverts the pulse and applies it to the base of transistor Q10. Q10 is thus turned on briefly (ie, for 100ms) to drive the piezo buzzer. The +12V to charge the 1000mF capacitor and allow the buzzer to beep is provided via a separate wire in the cable between the control box and the LED display, linking pin 1 of the two RJ12 connectors. It is controlled by switch S2 which therefore selects The display board is secured to the Perspex panel using M3 x 25mm tapped spacers and M3 x 6mm machine screws. 66  Silicon Chip siliconchip.com.au This is the fully-assembled display board. The LEDs are all mounted with the aid of a 14mm cardboard spacer which goes between their leads when soldering (see text). whether the buzzer sounds or not. There is also a 2.2kW resistor connected between pin 1 and the negative rail (ground) in the control box, to discharge the 1000mF capacitor fairly quickly if S2 is turned off after having been on. That’s about it, apart from a small green LED (LED57) in the control box to show when power is applied to the annunciator circuit. Construction All the components in the LED display section, apart from the piezo buzzer, are mounted on the main PC board which measures 185 x 102mm. This has rounded cutouts at each corner so it fits neatly inside a standard UB2-size jiffy box (197 x 113 x 63mm). The usual box lid is replaced by a 191 x 107mm rectangle of 3mm red Perspex, allowing you to see the number display. The PC board is mounted behind the Perspex panel using four M3 x 25mm tapped spacers and eight M3 x 6mm machine screws. The piezo buzzer mounts on the lefthand end of the box (near the rectangular hole for the RJ12 cable connector) and is secured using two 4G x 6mm self-tapping screws. The component overlay for the main PC board is shown in Fig.3. Begin assembly of the board by fitting the 10 wire links. They can be made from Table 2: Capacitor Codes Value 220nF 100nF 47nF 22nF μF Code 0.22µF 0.1µF .047µF .022µF EIA Code   224   104   473   223 IEC Code   220n   100n   47n   22n Table 1: Resistor Colour Codes o o o o o o o o o o siliconchip.com.au No.   1   1   1   2   1   1   3   7   7 Value 3.3MW 2.2MW 470kW 100kW 10kW 2.2kW 1kW 150W 100W 4-Band Code (1%) orange orange green brown red red green brown yellow violet yellow brown brown black yellow brown brown black orange brown red red red brown brown black red brown brown green brown brown brown black brown brown 5-Band Code (1%) orange orange black yellow brown red red black yellow brown yellow violet black orange brown brown black black orange brown brown black black red brown red red black brown brown brown black black brown brown brown green black black brown brown black black black brown December 2005  67 Fig.4: this is the parts layout for the control board, while at right is the matching photo. Note that the switches are soldered into place only after both they and the PC board have been mounted on the lid. Fig.5: here’s how the control box goes together. As with the display board, the LED is installed using a 14mm spacer. The top photo shows the control box lid with the two switches and the M3 x 15mm spacers in place, while the photo above shows the unit with the PC board in place. either 0.8mm tinned copper wire or resistor lead offcuts. That done, fit the RJ12 connector (CON1) and the small 2-way terminal block used to connect the wires from the piezo buzzer. Take care with the RJ12 socket. In particular, make sure that all four of its connection wires pass through their corresponding board holes before you push the socket’s plastic lugs through the larger holes. That’s because the connection wires are quite fine and can 68  Silicon Chip This side-on view clearly shows the control box assembly (but from the other side compared to the diagram above), while at right is the completed unit. otherwise be buckled when the socket clicks into position. After it has been fitted, you need to solder the wires underneath, of course. Next, fit the resistors and then the capacitors, starting with the smaller and lower value metallised polyester and multilayer monolithic types which are not polarised. The two electrolytics can then go in, making sure you fit these with the correct polarity. The two 1N4148 diodes are fitted with their cathode band ends towards the right. The three transistors in TO-126 packages (Q8, Q9 & Q10) are each fitted to the board with a 10mm long M3 machine screw and nut. In each case, the leads are bent down 5mm away from the body, so that they pass through the corresponding board holes when the transistor is screwed down. Once these parts are in, fit the BD139 transistor in the Q10 position. The two siliconchip.com.au Par t s Lis t – LED Annunciator Main Box 1 PC board, code 03112051, 185 x 102mm 1 UB2 plastic jiffy box (197 x 113 x 63mm) 1 3mm-thick red Perspex panel to match box, 191 x 107mm 4 M3 x 25mm tapped spacers 8 M3 x 6mm machine screws, round head 3 M3 x 10mm machine screws, round head 3 M3 nuts 1 12V piezo buzzer (Jaycar AB3462) 2 4G x 6mm self-tapping screws 1 RJ12 socket, PC board mounting (CON1) 1 2-way PC-mount LV terminal block – 5mm spacing (CON2) Fig.6: here are the drilling details for the control box. Semiconductors 1 4093B quad CMOS Schmitt NAND gate (IC1) 1 4553B 3-decade CMOS counter (IC2) 1 4511B BCD-to 7-segment decoder (IC3) 7 2N7000 N-channel MOSFETs (Q1-Q7) 2 BD140 PNP transistors (Q8, Q9) 1 BD139 NPN transistor (Q10) 56 5mm high brightness LEDs (LED1-LED56) 2 1N4148 diodes (D1,D2) Capacitors 1 1000mF 16V electrolytic 1 330mF 16V electrolytic 1 1.0mF MKT metallised polyester 1 220nF MKT metallised polyester 3 100nF multilayer monolithic 2 100nF MKT metallised polyester 1 47nF MKT metallised polyester 1 22nF MKT metallised polyester Resistors (0.25W 1%) 1 3.3MW 1 10kW 1 2.2MW 2 1kW 1 470kW 7 150W 2 100kW 7 100W Control Box 1 PC board, code 03112052, 76 x 46mm 1 3mm green LED (LED57) 1 UB5 plastic jiffy box (83 x 54 x 31mm) 1 pushbutton switch (S1 – Jaycar SP-0700) 1 round actuator SPDT rocker switch (S2 – Jaycar SK-0960) 1 RJ12 socket, PC board mounting (CON1) 1 2.5mm DC input socket, PC board mounting (CON2) 4 M3 x 15mm tapped spacers 4 M3 x 6mm machine screws, countersunk head 4 M3 x 6mm machine screws, round head 1 RJ12 6P/4C extension cable, 3m long (Jaycar YT-6040) Resistors (0.25W 1%) 1 2.2kW 1 1kW Where To Buy A Kit The development of this project has been sponsored by Jaycar Electronics and so kits for the LED Annunciator will only be available from Jaycar who hold the design copyright. The kit will retail for $59.95 (KC-5420), including the red Perspex lid for the display and a screen-printed lid for the controller box. BD140 transistors can then be installed in the Q8 & Q9 positions. Fitting the LEDs There are 56 red LEDs which form siliconchip.com.au the segments of the displays. These are all fitted with their longer anode leads towards the top of the board and their “flat” sides downwards, as shown in Fig.3. The LEDs are all fitted with the lower surface of their body about 14mm above the top of the board. Soldering the LEDs in with this uniform spacing is bit tedious but you’ll find it easier if you use a 14mm-wide strip of cardboard as a spacer under each group of four LEDs (ie, position the spacer between the leads). After the LEDs are all in place, fit the seven 2N7000 transistors (Q1-Q7) with their flat sides uppermost. Take care when you’re handling these transistors (and the three CMOS ICs), because they are MOSFET devices and can be damaged by electrostatic discharge. So discharge yourself before you handle December 2005  69 Fig.7: the main display box requires a cutout in one end to provide access to the RJ12 connector (CON1), plus three holes for the buzzer (two for mounting and one to feed the leads through, back into the box). them and solder their leads in place with an earthed soldering iron. Control box Everything in the small control box mounts on a PC board measuring 76 x 46mm, again with rounded corner cutouts so it fits inside a UB5 jiffy box. The board is attached to the rear of the box lid using four M3 x 15mm tapped spacers, plus four countersink-head M3 screws and four roundhead screws, all 6mm long. The component overlay is shown in Fig.4 while the box drilling details are shown in Fig.6. You need to drill and cut the box before you can assemble the PC board, as detailed below. Before the PC board is attached to the box lid, you need to install the RJ12 and DC input connectors, the two resistors and the 3mm green LED – see Fig.4. The LED is fitted with its body about 14mm up from the top of the board, so that it will protrude through the matching hole in the box lid. Make sure you fit it with its cathode “flat” towards the top of the board and its longer anode lead towards the 1kW resistor. Switches S1 and S2 are not fitted to the PC board but are mounted on the box lid. The smaller pushbutton (S1) is fitted in the hole on the left, with its two connection lugs aligned carefully in the North-South direction so they’ll pass through the matching slots in the 70  Silicon Chip PC board when it’s attached. The larger toggle/rocker switch S2 mounts in the hole on the right and is orientated so that its indexing key passes through the notch on the righthand side. This ensures that its connection lugs also pass through their matching board slots on the board. Once both switches have been fitted to the box lid, you can fit the four mounting spacers behind the lid as well, using four countersink-head M3 screws – see Fig.5. That done, offer up the PC board assembly from behind the lid, taking care to make sure that the LED passes through its hole in the lid and that the switch connection lugs pass through their board slots. When the board is resting on the spacers, secure it using the four roundhead M3 x 6mm screws. It’s then just a matter of soldering the switch connection lugs to their pads on the back of the board, to finish the control box wiring – see Fig.6. The two parts of your LED Annunciator should now be functional and ready for checkout. This is done before the main display board is attached to the spacers behind the Perspex front panel. Testing To text the unit, you’ll need a 12V DC regulated plugpack or a 12V battery. Either way, the supply needs to have a 2.5mm concentric plug at- tached to its output lead (if it doesn’t already have one), with the positive wire connecting to the plug’s centre contact and the negative wire to the outer sleeve. Don’t connect the control box to the main display board at this stage. Instead, just connect the 12V power supply to the control box, by plugging the 2.5mm DC plug into CON2, and check that the green power LED lights. If it doesn’t, you’ve either made a mistake in the wiring or the LED has been installed the wrong way around. OK so far? If so, switch off and connect the display board assembly to the control box using the phone extension cable with its RJ12 connectors. That done, reapply power and check that the display unit shows “00”. You should now be able to increment the displayed count by pressing pushbutton switch S1. Each time you do this, the reading should increase by one; ie, 01, 02, 03 and so on. Now temporarily connect the buzz­ er leads to the small terminal block CON2 (lefthand end of the main display board) and turn on switch S2. The piezo buzzer should now emit a short “beep” each time you release the pushbutton (S1). Now hold down S1. After about four seconds, the display should start increasing quickly. If that checks out, your LED Annunciator is working and you’re ready for the final assembly. Finishing up First, attach the piezo buzzer to the end of the box using a pair of 4G x 6mm long self-tapping screws, with its connection wires passing inside through the centre hole. That done, you can reconnect the wires to the terminal block on the main board. Next, fit four M3 x 25mm tapped spacers to the main board using four M3 x 6mm machine screws and attach the board to the rear of the front panel, again using four M3 x 6mm screws. That done, lower the panel and board assembly into the box, making sure the piezo buzzer wires are not strained or blocking the RJ12 socket access, and fit the four small self-tapping screws to hold it all together. Finally, if the 3m telephone cable supplied with the kit isn’t long enough for your intended application, longer cables are available from Jaycar stores and dealers, as well as from many other SC suppliers. siliconchip.com.au