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6-Digit Retro Nixie Clock Mk.2 . . . now with optional GPS time This revised 6-digit Nixie clock includes features such as GPSlocked time, date display, 7-day alarm, auto-dimming, 12/24 hour time and optional leading zero blanking. Having described the circuit and software operation in Pt.1 last month, this time we describe how to put the kit together. Pt.2: By Nicholas Vinen 64  Silicon Chip siliconchip.com.au HT A K 27k 1W 27k 1W 1 1 LED6 LED7 ND5 ND6 Q8 Q10 Q12 Q14 Q16 Q18 Q20 Q22 Q24 Q26 Q28 Q30 Q32 Q34 Q36 Q38 Q40 Q42 Q9 Q11 Q13 Q15 Q17 Q19 Q21 Q23 Q25 Q27 Q29 Q31 Q33 Q35 Q37 Q39 Q41 Q43 ND4 Q6 ND3 NT2 CON13 27k 1W Q7 LED5 K Q4 LED4 A K 27k 1W 330k 1W 1 1 NT1 A Q5 ND2 27k 1W 27k 1W 330k 1W 180Ω K Q2 ND1 Q1 CON12 2 A K Q3 LED3 CON15 CON14 LED2 3 A 1 1 UPPER (DISPLAY) BOARD 180Ω K 44 x 27k RESISTORS CONNECT BETWEEN THESE SLOTTED PADS AND THOSE ALONG FRONT OF LOWER PCB Q44 CON11 A CON10 1 (44 x 27k RESISTORS) 100nF IC3 74HC595 6 FASTRAX UP501 GPS RX 100 µF x3 (PATCH ANT) 22pF 1 X1 REG4 Nixie Clock Mk2 IC5 74HC595 IC4 74HC595 IC6 74HC595 10 µF 3.3V 5V 10k 47Ω 0.5W 100k 6.8k 220Ω TX 1PPS 22pF 100nF CON3 IC2 74HC595 100Ω 6.8k 100k RX +V IC1 PIC32MX170F256B Q51 27k 100nF ‘2' + 4004 D2 100nF 1 GND + 10Ω 10k 10k LK1 NC + + REG3 100nF REG2 + 47k 27k S2 S1 100nF Q50BC337 100nF Q52 ~ – + BR1~ PB1 100 µF x2 390k 2.7k LEDS CON2 (GlobalSat EM–406A GPS Rx) 1000 µF Q47 820Ω CON6 MPSA42 CON5 MPSA42 ‘3' CON9 BC327 D1 Q48 IRF740 4004 + 1nF BC337 ZD1 + REG1 34063 L1 10–12V 13V 220 µH 1000 µF 25V 100nF 4.7 µF 400V Q46 + CON8 HT BC337 Q49 CON1 LOWER (CONTROLLER) BOARD 19102151 1 RESISTORS FROM UPPER PCB CONNECT TO THESE SLOTTED PADS Fig.3: follow this PCB layout and wiring diagram to build the Nixie Clock. The sockets on the upper board are made from snapped sections of socket strip – note how they are arranged. The GPS module connections shown are for the Fastrax UP501; other modules will require different connections so refer to Fig.5 or the appropriate data sheet and observe the connector pin labelling. Once the two boards are joined by four spacers, the six wires between them can be connected and the 44 x 27kΩ resistors soldered into the slots along the front. T HE NIXIE CLOCK MK.2 comes exclusively as a kit from Gless Audio and there are various options, eg, whether or not the case is included. Regardless of which kit you choose, you will need to start by building the two boards and joining them together. Start by checking the slots along the front of the two double-sided boards. Due to the way the slots are made, some may be partially blocked with copper fragments. If so, use a small piece of stiff wire to clear them out. Now fit the small (0.25W and 0.5W) resistors on both boards. Use parts siliconchip.com.au layout diagram Fig.3 and the resistor colour code table (Table 1) to guide you. It’s a good idea to measure the resistors with a DMM before fitting them as resistor colour code bands can be hard to read. You will be left with a number of 27kΩ resistors. While two of these are fitted to the lower board, the rest will later be soldered between the two boards, so set them aside for now. Finishing the upper PCB Note that the upper board shown in Fig.3 has been changed slightly from the original and it’s possible you could get an earlier revision in the kit (the same one used in our photos). You can ignore the differences as they don’t affect operation in the slightest. Proceed to solder the eight 1W resistors in place on the upper board, as shown in Fig.3. Then, carefully snap the two 40-pin socket strips into 36 sections with two pins and then snap six single pins off the remaining strips. These form the Nixie tube sockets, arranged as shown in Fig.3. Check after soldering that each section is sitting right down on the PCB. March 2015  65 1F SUPERCAP + GLUE LDR1 A K IRX1 LED1 6mm 10 x 20mm BLACK CARD Fig.4: four components are soldered to the underside of the lower PCB as shown here. Note that two different sets of pads are provided for the supercap to suit different brands but the capacitor supplied with the kit is likely to use the outer pair. The small piece of black card is glued into place once all four of the parts shown have been fitted. The 44 high-voltage transistors can be installed next. These are all the same type. MPSA42 types will probably be supplied but MPSA44 and 2N6517 are valid alternatives. Note that there are several other similar-looking devices in the kit so put those aside first. Fit all 44 transistors on the upper board with the same orientation, ie, flat side to the right as shown in Fig.3. You will need to crank the leads out using The top PCB carries the six Nixie tube sockets (see text), the two Neon lamps, the 44 segment-driver transistors and the six blue LEDs which illuminate the bases of the Nixie tubes. Check that all parts are correctly seated and orientated before soldering their leads and note that the six LEDs are mounted on the bottom of the PCB (see photo on facing page). small pliers to suit the pad spacings on the PCB. Make sure that they are all pushed down fully before soldering – if they aren’t, when you go to fit the perspex cover later, you will find that it can’t be screwed down properly. Next come the six blue LEDs. These poke up through a hole in the middle of each socket but are actually fitted on the underside of the board and soldered to pads near the top edge. Start by bending one the LED’s leads down by 90° about 3mm from its body, at the same time ensuring that its polaity will be correct when it is mounted in position (see Fig.3). That done, cut a couple of lengths of small diameter heatshrink tubing and slip them over the leads so that they are insulated all Table 1: Resistor Colour Codes o o o o o o o o o o o o o o o No.   1   2   2   1   6   3   2   1   1   1   2   1   1   1 66  Silicon Chip Value 390kΩ 220kΩ 100kΩ 47kΩ 27kΩ 10kΩ 6.8kΩ 2.7kΩ 820Ω 220Ω 180Ω 100Ω 47Ω 10Ω 4-Band Code (1%) orange white yellow brown red red yellow brown brown black yellow brown yellow violet orange brown red violet orange brown brown black orange brown blue grey red brown red violet red brown grey red brown brown red red brown brown brown grey brown brown brown black brown brown yellow violet black brown brown black black brown the way from the LED’s lens until just before they reach its two solder pads. It’s then just a matter of bending the ends of the leads up to pass through these pads before shrinking the tubing down and soldering the leads in place. Repeat this procedure for the other five LEDs, checking the orientation in each case. The photo on the facing page shows the details. Finally, fit the two Neon lamps. Parts List Additions The Nixie Clock is built into a clear acrylic case. In next the parts Pt.2 monthlist haslast month, we left out constructional the 28-pin DIL socket for the full the microcontroller (IC1). Also, the details. case is held together with 16 selftapping screws rather than the 12 specified and it also includes four stick-on feet. 5-Band Code (1%) orange white black orange brown red red black orange brown brown black black orange brown yellow violet black red brown red violet black red brown brown black black red brown blue grey black brown brown red violet black brown brown grey red black black brown red red black black brown brown grey black black brown brown black black black brown yellow violet black gold brown brown black black gold brown siliconchip.com.au Right: the six Nixie tubes plug into the sockets but make sure they are correctly orientated. The Neons are mounted 10mm above the PCB. These are installed with the bottom of the glass envelopes 10mm above the top of the PCB and with the exposed leads covered with heatshrink tubing. The critical thing is that the leads are perpendicular to the PCB and that the two lamps are at the same height. These form the hour/minute and minute/second separators. If you cut the heatshrink sections all to the same length (around 11mm) prior to shrinking and keep them butted up against the underside of the lamps, these will then form natural spacers to allow you to get a consistent stand-off height between the two. Assembling the lower PCB Continue the lower PCB assembly by installing diodes D1 & D2 and zener diode ZD1. Check Fig.3 to see which goes where as there are three different types. Make sure that they are orientated as shown. After that, it’s a good idea to fit the four PCB pins for CON5, CON6, CON8 & CON9. This is because they are a tight fit and you will probably need to hammer them in before soldering. The tightness is so they don’t fall out when you flip the board over to solder them. Now mount the IC socket for microcontroller IC1, then install IC2-IC6 and REG1 which do not require sockets. Having said that, you may be supplied sockets for IC2-IC6 in which case you can use them; it does eliminate the possibility of accidentally soldering an IC in backwards which can be very difficult to fix! Regardless, be careful with the orientation – ensure that the notched end of the IC or socket goes to the top (IC1, REG1) or lefthand (ICs2-6) end of the PCB. In each case, solder two diagonal pins, then make sure the device is flat on the board and pushed down all the way before soldering the other pins. Fit crystal X1 next. Bend its leads as shown but make sure they don’t touch its case. You can use a component lead off-cut bent into a “U” shape and soldered to pads on either side of the can to hold the crystal down onto the board as the thin leads can be quite fragile. The two pushbuttons can go in next, pushed fully down onto the PCB. Follow with bridge rectifier The six blue LEDs are mounted on the underside of the top PCB. Bend their leads at right angles about 3mm from the lens so that they poke up through the holes in the middle of the Nixie sockets. siliconchip.com.au March arch 2015  67 The lower PCB carries the power supply, PIC microcontroller, the divider/counter circuits and the GPS receiver module. BR1 (watch its orientation) and the remaining TO-92 package devices, ie, Q46, Q47, Q49-Q52 and REG2-REG4. These involve three different transistor types and two different regulator types so don’t get them mixed up; refer to Fig.3 to see which type goes where. As before, you will need to crank the leads out before fitting them. Now flip the board over and fit the parts which go on the underside: IRX1, LED1 and LDR1. Fig.4 shows the details. Note that LED1’s and LDR1’s leads are bent down by 90° just behind the main body of each part. They are then fitted so that they hover just under the PCB (but not touching it). IRX1 should be pushed all the way down onto the PCB before being soldered. IRX1, LDR1 and LED1 are all orientated so that their lenses face the adjacent edge of the PCB. Make sure LED1’s anode (longer lead) goes through the hole marked “A”. The orientation of the LDR is not important. Leave off the supercap for now. As shown in Fig.4, you also need to cut and glue a piece of black card between LED1 and IRX1. This is to minimise the amount of light from the LED which reflects off the inside of the front panel of the case and straight back onto IRX1. Cut a 10 x 20mm piece of card out Time Zone Enhancements In the article last month, we gave a list of regions where the time zone and daylight savings rules would be automatically determined. Since then, we have been able to add much more time zone data. As a result of the now near-global coverage, the unit should be able to determine the correct time zone just about anywhere on Earth. If you’re reading this from McMurdo station, you may be out of luck though! The resulting compressed time zone database is just shy of 200KB, so it comfortably fits in the PIC32’s 256KB flash. We realise that few constructors will require global coverage as most will live in Australia, New Zealand with maybe a few in the UK, Canada and the USA. So you may wonder why we bothered doing the extra work. The reason is that a global time zone database that fits in a microcontroller seems like a useful thing in general and some readers may wish to use it in their own projects. As far as we know, this is the first publicly available database (and codebase) to offer global coverage in such a compact package. So by releasing the source code for this project, we’ve made it much easier for anybody wanting to build a truly global GPS clock using a low-cost, compact microcontroller. If you’re interested, download the source code from our website (www. siliconchip.com.au) and peruse it. The time zone data and handling functions should be easy to bring into your own software if you are familiar with the C language. 68  Silicon Chip and glue it as shown in Fig.4. We used hot-melt glue but neutral-cure silicone sealant would be a better choice. You can check that the card is correctly placed by temporarily fitting the short spacers to the underside of the PCB and dropping it into the case. The card should sit on (or hover just above) the base and should also be in contact with the front side of the case, or very nearly so. If it’s pressing on the case you can trim it for a better fit. Now go back to the top side of the board and install the 11 ceramic/ plastic-film capacitors, followed by the seven electrolytic capacitors in the locations shown in Fig.3. Note that the electros are polarised. The electrolytics all go in the same way except for the two near the upperlefthand corner of the PCB, which go in the other way around. Just be sure to orientate them as shown on Fig.3. The remaining tantalum/SMD cer­amic capacitors can go in now. If you’re supplied with a tantalum, this is polarised just like the aluminium electrolytics and will have a plus symbol printed on it. This goes towards the top of the board. If using an SMD ceramic instead, solder it to the pads on the top of the board; the orientation doesn’t matter. Now fit the pin headers for LK1, CON2, CON6 and optionally CON5. Follow with DC socket CON1, then install the piezo buzzer (PB1) with its positive terminal towards the bottom of the PCB – see Fig.3. If it has a protective sticker on top, peel it off now. siliconchip.com.au siliconchip.com.au TX +V 1PPS DIGILENT PmodGPS (3.3V) 3DF RX0 TX0 1PPS GND VCC CON7 NC GND RX TX +V 1PPS RXD CON7 NC TXD RF GND SOLUTIONS VDD GPS-622R VBAT (3.3V/5V) 1PPS PSE_SEL GND RX TX +V 1PPS 1 6 RX RX TX FASTRAX GND UP501 VDD (3.3V) VDD_B PPS CON7 NC GND RX TX +V 1PPS TO CON3 PIN 2 CON7 NC 1 GND GND VIN GLOBALSAT RX EM-406A TX (5V) GND 1PPS 6 CON7 NC 1 BOOT GND GMOUSE RX VK16E TX (3.3V/5V) VCC 1PPS ENA (3.3V) GND GLOBALSAT RX TX EM-408 VIN 5 6 Fig.5: how to wire up various GPS modules. Take care with the pin 1 orientation and note that the wiring shown for the UP501 is different from that shown in Fig.3. That’s because we’re showing the UP501 with its antenna facing down in this diagram but facing up in Fig.3. Also note that VK16E’s BOOT pin may be left unconnected and the GPS-622R’s VBAT pin can go to either CON3 (as for the UP501) or directly to the supercap positive terminal, which would give a longer ephemera retention time. 1 If you’re building the GPS-locked 1 Before going any further, it’s a good idea to apply power and check some voltages. If you have a bench supply, set it to 12V DC 500mA, otherwise use the plugpack. Make sure the board is on a non-conductive surface and keep well clear of the upper-left section while it is powered up and for one minute afterwards. This area of the board runs at 180V DC and it does bite – trust us! The current drain will be a few hundred milliamps initially as the supercap charges but it should eventually drop to a few tens of milliamps, most of this being the quiescent current of the high-voltage boost DC/ DC converter. Check the 3.3V and 5V pins on LK1, Fitting the GPS module 6 Initial power tests using the PCB pin near the lowerleft corner of the board as a ground reference. These should both be close to their nominal voltages. Also, check for 3.3V at pin 2 of CON3 at lower-right. Now without touching any nearby components, check the voltage at the upper-left PCB pin, just to the left of L1. This should be close to 180V DC. Switch off and wait one minute for the HV capacitor to discharge. Measure the high voltage pin again, as explained above and ensure it’s below 20V before proceeding. Assuming the voltages are all OK, you can finish the construction. Otherwise, check for correct component placement and orientation and for good solder joints, then repeat the tests. 1 You can now mount toroidal inductor L1. Ideally it should be glued to the PCB with some silicone sealant but the board likely won’t be subject to much vibration so you can get away without doing this. The last part to be installed on the top of the PCB is high-voltage Mosfet Q48. This is soldered in place with its metal tab facing inductor L1. All that’s left now is to mount the super capacitor on the underside of the PCB. There are two sets of holes to suit different types of capacitors; most likely the supplied part will fit the most widely spaced pads (see Fig.4). Make sure the supercap is installed with the correct polarity – its positive lead should be marked and this goes into the pad near ZD1. 7 This view shows how the LDR1, LED1, infrared receiver IRX1 & the supercap are installed on the underside of the upper PCB. version of the clock, it’s basically just a matter of running five or six wires from the module to CON7 and then attaching the module to the PCB. First, identify the connections on your module. Connections for a few common types of GPS receiver are shown in Fig.5. Be careful to check which is pin 1 since the pin ordering will depend on the orientation of the module, ie, if you flip it over, the wiring order will be reversed. If your module is not shown in Fig.5, refer to its data sheet. If there is a BOOT or ENA (enable) pin, determine whether it needs to be left floating or connected to GND or VDD for normal operation. If there is a VDD_B pin, check that the 3.3V back-up supply at pin 2 of CON3 will be suitable; in most cases, it will be. The module’s RX terminal goes to the pin labelled RX (pin 2), ie, this is labelled for the module and not for the micro. Most modules will either be supplied with a cable that plugs into a small onboard header or else will have a row of solder pads. If it came with a cable, cut it short, to about 22mm and strip a couple of millimetres of insulation off the end of each wire before tinning it. Otherwise, you will need to cut a similar length of ribbon cable and solder one end to the row of pads, with bare tinned wires at the other end. If there is a VDD_B wire, make it substantially longer than the others, at around 50mm, so it can reach pin 2 of CON3. There are two options for making the connections. You can either solder the bare wires directly to the pins of CON7 or you can attach a pin header plug (or cut up a cable with a header already attached). A plug obviously GND RX TX +V 1PPS CON7 NC GND RX TX +V 1PPS TO CON3 PIN 2 OR SUPERCAP + March 2015  69 This rear view shows how the completed top and bottom PCB assemblies are fastened together on 25mm tapped spacers, with the bottom board sitting on 12mm male/female spacers. Adjusting For Accurate Timekeeping Without GPS Assuming a relatively stable ambient temperature, the unit can be adjusted to be out by less than one second per month. The easiest way to do this is as follows: (1) Set the time using an accurate reference such as the speaking clock service (phone 1194 in Australia or 0900 45678 in New Zealand). Make a note of the date that you do this. You don’t have to set the clock to be precisely correct, as long as you know how much it’s off by. If it isn’t precise, make a note of the number of seconds error. For example, if you’ve set the clock to say 09:00:00 at 9:00:02am on March 15th, the error is -2 seconds. (2) Leave the clock for some time – a week is sufficient but longer is better. (3) Using the same accurate time source you used earlier, compare the time on your clock to this more accurate time source. So, for example, let’s say your clock reads 10:08:33am but the speaking clock service says it’s 10:08:12am on March 23rd. The error is now -21 seconds. Make a note of this and also of the current date. (4) Subtract the first error from the second error. In this case, the result is -19 seconds. If the time was set precisely during the first step, this will not affect the error noted in step three above. (5) Determine the number of days that have passed between steps one and three. In our example, it’s eight days (23 -15). (6) Multiply the error from step four by 1024, then divide by the number of days from step five and divide again by 45. The result in this case is -21 x 1024 ÷ 8 ÷ 45 = -59.7 which we round to -60. (7) Go into crystal frequency trim mode (see panel on control interface) and add the number calculated above to the reading. So, in this case, if the current reading was 500, you would need to adjust it to give 440 instead. Save the changes and that should cancel out most or all of the error. (8) If you notice over many weeks or months that the clock is slowly gaining or losing time, adjust the trim value in single steps. Make it higher if the clock is falling behind or lower if the clock is going too fast. 70  Silicon Chip makes it easier to remove the module later, however this is not normally required and it’s certainly quicker to solder them direct. In theory, the GPS module should be orientated with its ceramic patch antenna facing up. However, we experimented with both orientations and found that it made little difference to sensitivity. If soldering the wires directly to CON7, mount the module first. Otherwise, once the plug has been wired up, plug it in and then mount the module. Smaller modules such as the Fastrax UP501, GlobalSat EM-406A and VK­16E can be fitted directly on top of the PCB using some double-sided tape. However, in practice, it’s preferable for them to be further away from the ground plane, so it’s better to attach them using a non-conductive spacer. Larger modules will require a spacer to clear surrounding components. The spacer can be made from plastic or a non-conductive type of stiff foam and attached to the board and the module itself using double-sided tape. Use multiple layers of plastic if necessary to create a thick enough spacer. We used polyethylene foam since we happened to have some handy but a more rigid material is better. Once the GPS module is in place, siliconchip.com.au same method as before. Now continue by placing two more resistors between the three already soldered in, and keep “bisecting” in this manner until all the resistors are in place. This method gives you the best chance of getting them all to line up without the gaps increasing or decreasing as you go. Once they’re all in place go back over all the solder joints and make sure they have sufficient solder and have flowed properly before trimming off any excess lead length remaining. More testing Above: the 44 x 27kΩ resistors are strung between the two PCBs and soldered to slotted solder pads along the front edges. Make sure that the resistor leads are straight and use a ruler to ensure that they line up neatly (see text). fit the shorting block to LK1 to set the required supply voltage (3.3V or 5V). Joining the two boards Now plug IC1 into its socket. You will probably need to straighten its pins first. Make sure that the pins all go into the socket. Also, plug in the other ICs if using sockets for them as well. The next step is to cut two 60mm lengths and four 40mm lengths of mains-rated medium-duty hook-up wire. Strip and tin both ends, then solder one end of each to each of CON11-CON15 from the underside of the upper PCB. The two longer wires are for CON13. Now place the upper board upsidedown behind the lower board (rightside up) and solder the wires to the PCB pins (CON5, CON6, CON8 & CON9) and 2-pin header (CON2) on the lower board as shown in Fig.3. It’s easiest to start at the back and work your way to the front of the lower board. Make sure the wires to CON2 aren’t reversed or the LEDs won’t light up. Having done that, fit a 12mm male/ female tapped spacer to one of the mounting holes on the lower board from the underside, then attach a 25mm tapped spacer on the top side. Do this up tight, then repeat for the other three mounting holes. You can siliconchip.com.au then fasten the two boards together using four M3 x 6mm, pan-head screws. Do these up firmly and make sure the six wires are still connected at both ends and neatly tucked away. The next step is to fit the 44 27kΩ resistors into the slots along the front of both boards. It’s important that the bodies of these resistors are lined up carefully so that the finished clock looks neat. The following procedure is recommended. Try to avoid bending the resistor leads when removing them from the strip they are supplied on. Take two resistors with nice, straight leads and insert them into the pair of slots at the far left and far right ends of the boards. Next, use a small ruler to measure the distance between each resistor’s body and the top and bottom boards and move the resistors up and down until those distances are equal. Solder one end of each device, then check that the each resistor is still centred properly before soldering its other end. That done, insert another resistor between two slots near the middle (make sure the slots correspond!) and place the ruler horizontally so that it lines up with the bottom of the resistor bodies at either end. Adjust the middle resistor so it too is aligned with the ruler and solder it in place using the The Nixie tubes can now be unpacked and plugged into their sockets. Before plugging them in, you will need to remove the plastic spacer and carefully trim the leads to exactly 5mm long, measured from the glass base of the tube. Make sure the leads are all straight, then gently place one tube on top of one of the sockets with each lead sitting in the cup of its socket pin. Now slowly push the tube into its socket. If any of the pins are not properly in the socket or if any starts to bend during insertion, remove the tube and fix that pin, then try again. It should go in with gentle pressure. Fit the other five tubes in a similar manner, then make sure the whole assembly is clear of any conductive items such as loose bits of wire and solder. With the plugpack disconnected from the mains, plug it into CON1, then keep yourself clear of the board assembly while powering it up. Be careful during testing: as stated, the HT supply is around 180V DC and it can give you a nasty shock if you come into contact with it! Don’t touch or work on the unit when the plugpack is connected. In addition, wait 15 seconds for the 10μF 250V capacitor to discharge after switch off before touching the unit. It should be safe once the Neon lamps have gone out but if in doubt, measure the HT voltage rail. The Nixie Clock performs a display test initially, so you should see all six zero segments light up, followed by one, two, three etc. Note that the first, third and fifth tubes will only display digits up to three, five and five respectively so don’t be concerned that they do not light when the other tubes are showing six, seven, eight etc. The unit should also emit a short beep briefly after power is applied, March 2015  71 Using The Control Interface The clock is set up and controlled using the two rear-mounted pushbuttons and the front proximity sensor. We refer to the pushbuttons as “left button” and “right button”; this is the orientation when the digits of the clock are facing you. Below, we talk about short and long presses. A short press is under one second (typically, 250-500ms) while a long press is for more than one second. Some actions require the buttons to be pressed simultaneously. A number of settings are stored in the microcontroller’s flash memory so they are effectively permanent, even if power is lost for long periods. These are: LED status (blue LEDs on/off), 12/24 hour time setting, leading zero blanking setting, timing crystal trim value, alarm time and days, time zone (if a GPS module is fitted) and LED/Nixie dimming settings. The various actions that can be performed using the buttons are: • • To turn blue LEDs on/off: press both buttons, then release simultaneously after a short duration (around half a second). To set time and/or date (no GPS fitted): long press left button. Time is frozen and one digit flashes. Short press left button to increment digit, short press right button to move to next digit. To switch between setting time and date, long press right button. When finished setting, long press left button. • To set the time zone (GPS fitted): long press left button. Flashing “00” indicates automatic time zone & daylight saving mode. Short press left/right buttons to change to manual mode and set time zone offset in 15-minute intervals. With time zone set manually, daylight saving is disabled. Long press left button to save changes, long press right button to abort. To go back to automatic TZ/DST, go into time zone setting mode and press left/right button until flashing “00” is displayed again. • To switch between 12-hour time and 24-hour time: go into time set or time zone set mode (long press left button), then hold down both buttons for at least one second and release simultaneously. • To show the date: short press left button or briefly place your hand close to the proximity sensor at the lower front of the unit (within a few centimetres of the case). • To set alarm: long press right button. Set alarm time using the same procedure as outlined for setting the time above. By default, alarm sounds during week days only. To change, long press right button. Days are shown as 0123456 with 0 = Sunday, 1 = Monday, etc. Days for which alarm is enabled are lit, disabled days are off. Short press left button to toggle alarm setting for current (flashing/pulsing) day. Short press right button to move to the next day. Long press right button to return to setting alarm time; long press left button in either mode to save settings and enable alarm. • To show alarm time: short press right button. Alarm time is shown for 10 seconds, then it goes back to displaying the current time. If alarm is on, display during this time is solid, otherwise it flashes. • • To turn alarm on/off: show alarm time as described above, then short press left button to toggle alarm on/off. To cancel/snooze alarm: trigger proximity sensor (as described above for date display) for 10-minute snooze. Short press either button to cancel alarm. • To trim out crystal frequency error (not required when GPS module fitted): hold down both buttons for at least one second, then release simultaneously. Adjustment is initially 500; higher values (up to 999) make clock run faster, lower values make it run slower. Short press left and right buttons to reduce/increase trim value. Long press left button to save changes, long press right button to abort. See accompanying panel for how to determine the correct value. • To enable or disable leading zero blanking (generally used in 12-hour time mode): go into crystal trim mode (see above), then after releasing buttons, hold down both buttons again for at least one second and release simultaneously. By default, leading zero blanking is not enabled, so this will enable it. Use the same procedure to turn it off again. • To enable or adjust auto-dimming: both the Nixie tubes and the blue LEDs can be set to automatically dim as the ambient light level drops (as sensed by the onboard LDR). There is a dimming factor value for each. If set to zero, they will always operate at full brightness. For numbers greater than zero, larger numbers mean faster dimming as the ambient light level drops, up to a maximum value of 20, with a default value of eight. To set the LED dim factor, hold down the right button for at least one second, then press the left button and quickly release both. The left and right buttons are then used to change the value with a long press of the left button to exit. Setting the Nixie tube brightness is identical but reverse the initial long/short button presses (ie, hold down the left button then briefly press left). verifying that the piezo buzzer works. Having gone through the digit test, you will then see a display of “00.00.00” with the first digit flashing, indicating that the time has not yet been set. Check that the blue LEDs are lit. If anything goes wrong, switch off and check the assembly for faults. If one or more segments are not lighting, first check that the tube is inserted 72  Silicon Chip properly in the socket and that the resistors along the front of the unit are all soldered properly. Otherwise, it could be a suspect solder joint on one of the ICs. If you don’t get any display, that suggests a problem with IC1 or its associated crystal oscillator. Nothing will function if the oscillator isn’t working. If the Neon lamps don’t light, that suggests a problem with the boost generator or wiring as they are permanently wired across the HV rail. If it checks out, switch off and wait 15 seconds after the Neons go out before touching the board assembly. Putting the case together The case is made from six pieces of acrylic, one black and five clear, held siliconchip.com.au Where To Buy A Kit The Nixie Clock Mk2 will be available exclusively as a complete kit from Gless Audio. This includes the PCBs, all components, a programmed microcontroller, Nixie tubes and the case hardware. Kits should be available late February/early March 2015. Contact Gless Audio on 0403 055 374 or email glesstron<at>msn.com together with 16 self-tapping screws which go into pre-drilled holes. Start by attaching the thicker clear front and side panels to the base panel using six of the supplied self-tapping screws. Next, attach the thinner clear rear panel to the sides with four more screws. You can now affix the feet to the base. Position them horizontally just within the PCB mounting holes, 5mm from the front edge of the base and 10mm from the rear edge. Now temporarily remove the Nixie tubes from the PCB assembly before lowering it into the case, positioned towards the front. Once it’s resting on the base, slide it back so that the pushbuttons pop through the routed access slot at the rear. You can then secure the whole thing in place using four M3 pan-head screws up through the mounting holes in the base. Do them up nice and tight. Now fit the lid using the six remaining self-tapping screws. Once it’s in place, you can carefully plug the Nixie tubes back in. This is the completed Nixie Clock in its clear acrylic case. The case comes precut and drilled and is secured using the supplied metal screws. Final testing & operation With everything now inside the case, re-apply power. If you’ve fitted a GPS module, the display brightness will vary in a pulsating fashion until a position fix has been obtained. If you don’t get a fix after 30 minutes or so, try moving the unit to a less obstructed position, such as near a window. If the fix is lost, the unit will switch over to using its own crystal and the brightness will pulsate until it again has a reliable GPS fix. If you aren’t using a GPS module and the time has not yet been set, refer to the panel titled “Using the Control Interface” for instruction on using the two rear panel pushbuttons to set the time. When first powered up, the unit is already in time set mode, so it isn’t necessary to hold down the lefthand button to get into that mode. Don’t forget to set the date, too. Once that’s done, you can check siliconchip.com.au Fig.6: a Google Earth view showing some of the time zone regions used to cal­ culate local time. These shapes have been simplified as much as possible, to save flash memory storage space, without compromising the accuracy of determining the correct zone for any latitude/longitude on land. For example, where they overlap, only the border of the time zone analysed first has to be accurate as areas within this zone are excluded before the latter zone is checked. the operation of the proximity sensor. We’ve made it relatively insensitive to prevent false triggering so you will need to place your hand up close to the front of the unit, possibly touching it. If nothing happens, try moving it closer to the sensor. Once it’s triggered, you should see the display change to show the date and then go back to time after 10 seconds. You can now set up the various preferences to your liking. Refer to the instructions in the accompanying panel for turning the LEDs on/off, changing between 12/24 hour time and enabling leading zero blanking, if desired. If using the crystal for timekeeping (ie, no GPS) you can also start the calibration procedure as explained in that panel and there are also instructions there for setting the alarm if required. Note that the alarm can be put into a 10-minute snooze using the proximity sensor but a press of either one of the rear panel buttons is required to actually shut it off when it sounds. SC March 2015  73