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Build your own LIGHTSHOW Last month we presented the circuit details for the 12V Light Show and this month we conclude with the constructional details for the AC and DC versions, as well as a light display box using 20W halogen lamps. PART 2: By LEO SIMPSON & RICK WALTERS The Light Show is mounted in a plastic instrument case which measures 260 x 180 x 65mm. Inside there are two PC boards, the main board measuring 236 x 160mm (code 01112971) and the smaller front panel board measuring 120 x 49mm. The 66  Silicon Chip front panel board is mounted vertically behind the front panel (funnily enough) and is secured to the panel by the mounting bushes of the six miniature toggle switches. There are quite a few connections between the main PC board and the front panel board and these are taken care of by six wires to the Input (S1) and Beat (S5) switches and a 16-way cable between header sockets on both boards. Board assembly Let’s talk about the front panel board first since it is the easiest to assemble. Its component overlay is shown in Fig.1. First, mount the switches on the board. Their lugs are inserted from the component side and soldered. Make sure that each switch is sitting perpendicular to the board before soldering the lugs. That done, insert the 16-pin socket for the cable header and solder it in place. Next, insert and solder the four red LEDs. These should be mounted This photo shows the interior details of the 12V DC version of the Light Show. Note the position of the red strip on the 16-way ribbon cable that’s used to connect the switch board to the main PC board. with their full lead length so that they stand about 15mm above the board. This enables them to fit easily into the bezels on the front panel. That part comes later. The next part is tricky and involves making the 16-way header cable. don’t worry, it will still work when you crimp the other end of the cable. The 16-way grey ribbon cable we used comes with a red stripe on one side and this should be aligned with the pin 1 end of the header at both ends. You can confirm this by looking at the photos in this article. Having passed this hurdle, it is time to move onto the more straightforward assembly of the main PC board. Its component overlay is shown in Fig.2. First check the bare board for any undrilled holes, broken tracks, shorts between tracks or evidence of thermonuclear damage before installing any components. Fix any defects and check that the two small cutouts at Terminating the ribbon cable While most kitset suppliers will probably include an assem­bled header cable, you will certainly need to make it if you are not building this project from a kit. The easiest way, if you don’t have a crimping tool, is to plug the header into the extra 16-pin IC socket (specified in the parts list), then feed the cable into the top of the header. The assembly can now be care­fully squeezed together in a vice, making sure the ribbon is sitting flat and square in the header. You will squash the pins in the socket and it may snap but Fig.1: component overlay for the front panel PC board. February 1998  67 Fig.2: component overlay for the main PC board. Take care to ensure that all polarised parts are correctly mounted. 68  Silicon Chip Table 1: Resistor Colour Codes ❏ No. ❏   2 ❏   1 ❏   3 ❏   4 ❏   3 ❏   3 ❏   1 ❏   1 ❏   1 ❏   8 ❏   1 ❏   4 ❏ 18 ❏   2 ❏   2 ❏   2 ❏   1 ❏   1 ❏   6 ❏   1 ❏   1 Value 1MΩ 510kΩ 470kΩ 220kΩ 180kΩ 100kΩ 47kΩ 39kΩ 27kΩ 22kΩ 18kΩ 11kΩ 10kΩ 5.6kΩ 4.7kΩ 3.3kΩ 2.2kΩ 1.8kΩ 1kΩ 470Ω 68Ω each end of the board have been made to allow it to clear the front pillars in the case. Then proceed by fitting and soldering the 36 wire links and 17 PC pins. These can be followed by the diodes, resistors, IC sockets and trim­ pots. Then insert the capacitors, making sure that all the electrolytics are installed with the correct polarity. Note the 68Ω 1W resistor on the lefthand edge of the PC board. This is only required if you are building the circuit for AC operation; ie, with a 12V transformer powered from the 240VAC mains. If you are building the Light Show to be powered from a 12V battery, the 68Ω resistor can be omitted and a wire link fitted instead. The electret microphone insert is wired directly to two PC stakes on the board. No shielded cable is necessary. The four Mosfets (Q1-Q4) are mounted in a straight line and require no heatsinks. Lastly, mount the two potentio­ meters (VR5 & VR6) on the PC board. Case assembly We will assume that you are building a kit which has the front and rear panels already drilled for you. If not, you will have to use the front panel artwork (Fig.8) as a drilling template 4-Band Code (1%) brown black green brown green brown yellow brown yellow violet yellow brown red red yellow brown brown grey yellow brown brown black yellow brown yellow violet orange brown orange white orange brown red violet orange brown red red orange brown brown grey orange brown brown brown orange brown brown black orange brown green blue red brown yellow violet red brown orange orange red brown red red red brown brown grey red brown brown black red brown yellow violet brown brown blue grey black brown before assembly can proceed. The first step is to attach the front panel to the two potentiometers on the main board, using the pot nuts and washers. Solder one of the headers of the 16-way cable to the socket position on the front panel board (note: no socket is actually fitted in this position). Make sure that the red stripe of the cable is closest to the LEDs. Then attach the board to the front panel using the six toggle switches as the anchor points. You will need to use spacer nuts on the switch bushes so that the four LEDs protrude through their respective bezels by the right amount. Table 2: Capacitor Codes ❏ ❏ ❏ ❏ ❏ ❏ ❏ ❏ ❏ ❏ ❏ Value IEC Code EIA Code 0.12µF   120n   124 0.1µF   100n   104 .068µF   68n  683 .056µF   56n  563 .047µF   47n  473 .033µF   33n  333 .022µF   22n  223 .015µF   15n  153 .0068µF   6n8  682 .0022µF   2n2  222 5-Band Code (1%) brown black black yellow brown green brown black orange brown yellow violet black orange brown red red black orange brown brown grey black orange brown brown black black orange brown yellow violet black red brown orange white black red brown red violet black red brown red red black red brown brown grey black red brown brown brown black red brown brown black black red brown green blue black brown brown yellow violet black brown brown orange orange black brown brown red red black brown brown brown grey black brown brown brown black black brown brown yellow violet black black brown blue grey black gold brown Then attach the free end of the 16way cable to the header socket on the main board. As noted before, the red stripe in the cable should line up with the pin 1 end of both header sockets. You can now fit the main board into the case but before doing so, remove the two integral plastic mounting pillars at the front of the case. These pillars would otherwise foul the under­ side of the PC board. Fit the PC board into the base of the case and secure it with the two self-tapping screws, at the rear of the board. The wiring from the switches to the PC board can be seen in Fig.3. Complete the wiring to the rear panel, as shown in Fig.3. So far then, we have completed the DC version of the Light Show. Testing You can initially test the board without the halogen lamps connected as the front panel channel LEDs will mimic them. Set the BEAT switch to OSCILLATOR, the DISPLAY switch to UNMODULATED, the PATTERN switch to CHASER and the DIRECTION switch to FORWARD. Connect a 12V battery or DC power supply to the battery input terminals and turn the POWER switch on. The power LED should light and the February 1998  69 Fig.3: this diagram shows the wiring details for the 12V DC version of the Light Show. The terminal blocks shown dotted mount on the back of the rear panel. channel LEDs should light in sequence from left to right. If the DIRECTION switch is set to REVERSE these LEDs should chase in the opposite direction. The stepping speed should vary as the SPEED control is turned. In the AUTO position the sequence should reverse every minute or so. Turn the PATTERN switch to 70  Silicon Chip STROBE and all four LEDs should pulse on and off, again varied by the SPEED control. Similarly, when ALTERNATE is selected, channels one and two should turn on and alternate with channels three and four. So far so good. Now turn the BEAT switch to INPUT and set the INPUT switch to MICROPHONE. Turn the front panel LEVEL con­trol to maximum, turn VR1 to VR4 fully clockwise, then tap the PC board gently near the microphone. Each time you tap, the pairs should alternate. If this is the case the only test left is the lamp modulation. Turn the display switch to DISCO and sing or whistle into the microphone. If you lack these skills turn up the stereo and watch the intensity of the LEDs vary with the volume and frequen­cy of the music. This photo shows the interior details of the 12V AC version of the Light Show. The main difference is the addition of the bridge rectifier on the metal rear panel of the case and the 39V 5W zener diode across the 12V input terminals on the main PC board. Finally, you should connect the four 20W or 50W halogen lamps and check that all functions are correct. AC operation The unit as described so far has been designed to operate from a 12V DC supply or car battery. If you want to operate from 12V AC, it needs a few mods to allow it to run from a suitable transformer. Essentially, the modifications required are the fitting of a bridge rectifier to the rear panel which then acts as a heatsink, the addition of a 39V 5W zener diode across the supply following the 10A fuse and a 68Ω 1W resistor in series with the 3-terminal regulator. The modified power supply circuit is shown in Fig.4. If you are using 20W halogen lamps, a suitable transformer for the AC version is the 12V 63VA halogen lamp transformer available from Jaycar Electronics (Cat MP-3050). The beauty of this trans­former is that it is completely shrouded in a plastic case and is supplied with a two-core mains flex and plug. Hence, it can be mounted outside the chassis and will not present a safety hazard. By the way, you could also use a large 12V battery charger if you have one on hand. Its rating should be 6A or more, if you are using 20W lamps. If you are going to use 50W lamps, you would need a much larger charger, rated at 15A or more. Alternatively, you need a 12V transformer with a rating of 160VA or more. This will need to be installed in a suitable case. The relevant wiring details for the AC version of the Light Show are shown in Fig.5. The 39V 5W zener diode is wired directly across the DC input pins. Once you have wired up the AC version of the circuit, apply power and check that all of the above tests are OK. Then check its operation with the halogen lamps. If you are using 50W halo­gen lamps, you will find that the rear panel of the Light Show will become quite warm, due to the heat dissipation in the bridge rectifier. AC/DC operation If you have built the AC version of Fig.4: the power supply for the AC version incorporates a 12V AC transformer, a bridge rectifier and a 39V 5W zener diode. The zener diode damps spike voltages from the transformer which are generated by the switching action of the Mosfets. February 1998  71 Fig.5: wiring details for the 12V AC version of the Light Show. Note that this version has a 68Ω resistor on the motherboard at extreme left, plus ZD1 and a few extra parts on the rear panel. If you need still more gain, reduce the 3.3kΩ resistor at pin 2 of IC1a to 1.5kΩ. the circuit, it is still feasible to operate it from a 12V battery if you want to. However, you will need to install a switch to short out the 68Ω 1W supply resistor when operating in the DC condition. Troubleshooting More audio gain The input sensitivity of the unit was 72  Silicon Chip set to be driven by speaker level from a typical stereo amplifier or a standard CD player. If you use a portable CD player, the output level is likely to be somewhat lower and the audio sensitivity may be insufficient. If this proves to be the case, removing the 1.8kΩ resistor at the external input will give additional gain. Provided that you have followed the wiring diagrams care­fully, your Light Show should work first time. But we have to admit that Murphy’s Law applies here just as well as anywhere so there is always the possibility that it might not work. If so, the most likely causes are simple things like broken February 1998  73 Fig.6: actual size artwork for the main PC board. Note the cutout in each end of the board. These must be there to allow clearance for the front pillars of the case. Our new Light Show drives 12V halogen lamps and can provide a variety of disco and chaser patterns. It runs from 12V DC or AC and can be used virtually anywhere. tracks on the PC board, missed solder joints and connections or solder bridges between tracks. Of course, you might also put a wrong component value in and this can cause the circuit to misbehave. A very careful visual check is the first step in finding the cause of circuit problems. If none of the above applies and your Light Show still doesn’t work (dammit), the next step is to check all the voltages on the circuit. If these are not as they should be in any section, you are well on your way to finding the solution. The block diagram on page 20 of the January 1998 issue also gives you a guide to the circuit functions and this can be helpful when you are trying to sort out problems. Typical situations We made our light display with a painted timber frame and with the lamp sockets mounted directly on the base. Do not use lamps rated at more than 20W, as this could present a fire hazard. 74  Silicon Chip As a guide, let’s look at some typical situations: Symptom: front panel LEDs work but one of the halogen lamps doesn’t. Check: wiring to the lamp and that the lamp itself is OK. Symptom: one channel fails to modulate when the DISPLAY switch is set to DISC mode. Check: filter circuit, rectifier and comparator for that channel. Note that the output of each op amp filter stage should be close to 0V DC. Under no-signal conditions, the outputs of the compara­ tor stages (IC3a-IC3d) should all be low. Symptom: unit works when the INPUT switch is in the External pattern display beat input speed unmod input microphone alternate auto direction reverse 6.2 strobe 6.2 6.2 6.2 mod 6.2 level 6.2 power forward chaser disco 7.0 7.0 You will probably have your own ideas on how you want to build the light display but we’ll still tell you how we made ours. Our display was made of scrap timber with a white Perspex front to diffuse the light. The frame measures 650 x 360 x 60mm. The four lamp holders were equally spaced and screwed to but held off the base with 5mm spacers. This prevents the wires from being jammed under the sockets. A five connector strip was screwed to the back panel and one wire from each lamp was connected as the common to one termi­nal. The other four wires were connected, one to each remaining terminal. A five wire cable was plaited and connected to the terminal strip on the rear of the Light Show. Four sheets of coloured cellophane were purchased from a newsagent. These were cut to 600mm, rolled and sticky taped into rough 40mm tubes to form coloured diffusers for the lamps. You can see the general arrangement from the photos. Note that this arrangement is only suitable for 20W lamps (or lower). Do not use higher rated lamps if you intend building a similar lightbox to the one described here as the heat generated by them could easily cause SC the cellophane to catch fire. external Light display housing oscillator the waveforms around IC3 should be checked with an oscilloscope to see that they match those in Fig.3 on page 21 of the January 1998 issue. Well that’s a fairly comprehensive list of possible faults. The trick is to isolate the fault to a particular part of the circuit and then critically examine that circuit section. 6.2 position but not in the Microphone position. Check: the electret microphone circuitry associated with op amp IC1b. There should be about 6V DC across the electret. Symptom: unit works only when the DISPLAY switch is set to the UNMOD position and the BEAT switch is set to Oscillator. Check: wiring to INPUT switch S1, level control VR5 and the circuitry associated with op amp IC1a. Symptom: lights do not chase or strobe when BEAT switch is set to Oscillator. Check: circuit associated with oscillator IC1c. If you set the SPEED control to a low setting, you can check the oscillator operation with an analog multimeter set to measure 10VDC; ie, the pointer will swing back and forth at the frequency of oscil­lation. You can also check with your multimeter to see that pins 6 & 11 of IC6 are also oscillating at the same rate. If not, check around IC6 and the wiring to the BEAT switch. Symptom: the light pattern fails to automatically reverse after every minute or so, when the DIRECTION switch is set to AUTO. Check: the wiring to the DIRECTION switch and the circuitry associated with IC4b. You can check with your analog multimeter to see that the output of IC4b is switching high and low at about one-minute intervals as the 100µF capacitor charges and discharg­es. Symptom: lamps stay on in DISCO and MOD modes. Check: the ramp voltage from IC4d does not stay low all the time. If so, check the operation of IC4d. The voltage at the output of IC4d, pin 11, should be about +2.3V. Ideally, ch4 ch3 ch2 ch1 6.2 6.2 6.2 6.2 Fig.7: actual size artwork for the front panel PC board. Fig.8 at right shows the actual size artwork for the front panel. February 1998  75