Fullscreen HTML5Med Res (??MB)HTML4

Building the Discolight, Pt.2 Despite the circuit complexity, the Discolight is easy to build. This month, we give you the full construction and troubleshooting details. By GREG SWAIN Last month, we introduced our new Discolight light show and described its various features and the circuit operation. We're very proud of the circuit. It's an extremely versatile unit that should ser the standard for years to come. By now, you've probably taken a close look at the circuit and concluded that such a complicated looking beast must also be complicated to build and get going. But it's not. Many of the circuit elements are hidden inside multielement ICs and these, together with most of the other parts, are mounted on a single large printed circuit board (PCB). If you can follow the wiring 42 SILICON CHIP & JOHN CLARKE diagram shown in Fig.4, you should have little difficulty building this project. Even so, this is not a project that we recommend for beginners. As noted last month, part of the circuit is powered directly from the 240V AC mains supply and is therefore potentially hazardous (see warning panel). So take great care with the Discolight. If the circuit is not built and tested correctly, you could receive quite a nasty shock (or worse). Buying the parts By far the easiest way to collect the parts for this project is to buy the complete kit. At least three ma- jor retailers will be stocking kits and these will be supplied complete with pre-punched chassis and silkscreened front panel labels. If you do elect to go it alone, you should have little difficulty in buying the parts separately. The only parts that may initially cause problems are the isolated tab Triacs so be sure to check their availability before going in too deep. We expect that retailers will offer the Triacs separately once the initial demand for kits has been satisfied. Everything else, including the surface-mount mains sockets and the ICs, are standard items. The PCB will be available separately from the usual sources (see address panel on page 96). Starting construction It is a good idea to carefully inspect the copper side of the PCB before mounting any of the parts. While most boards will be quite OK, you might just be unlucky enough to get a board that has not been cleanly etched. In particular, look for small breaks in the copper tracks or very fine bridges between tracks. A little detective work at this stage can save a lot of trauma later on. Fig.4 shows where all the parts go on the PCB (code SC101688, 218 x 172mm). No particular order need be followed here although it's best to mount the small components first. These include the wire links, resistors, ICs and diodes. Be sure to use the correct part at each location and check that the ICs and diodes are correctly oriented before soldering the leads. It's quite easy to identify pin 1 of an IC. This pin is always adjacent to a small notch (or sometimes a dot) in one end of the plastic body (see Fig.4). You can use tinned copper wire for most of the wire links but note that the three links along the rear of the board must be run using insulated 240VAC cable. These three leads interconnect the A2 terminals of the Triacs (Q1-Q4) and are run in parallel with copper tracks on the PCB to ensure adequate current capacity. Once the low-profile parts have been installed, you can install PC stakes at the external wiring points shown numbered on the PCB (but not at location 7). PC stakes are also used to support the electret microphone and to terminate the transformer secondary leads. Do not use PC stakes to terminate the active (A) leads from the mains sockets - these leads must be soldered to the PCB. Similarly, the active lead from the mains fuse must be soldered to location 7 on the PCB. We'll say more about this later. The capacitors, trimpots and 3-terminal regulators can be installed next. Be careful with the orientation of the electrolytic capacitors and make sure that you don't confuse the two regulators. If you put the 7812 in where the 7912 should go (and vice versa), you'll have trouble for sure. The pin-outs for the regulators are shown on the circuit diagram (Fig.3 on page 60 of the July issue). The four toroid coils (11-14) in the interference suppression circuit are wound using 29 turns of 0.63mm enamelled copper wire. This close-up view shows how the insulated tab Triac Ql (at end of pen) is mounted on the PCB and bolted to the rear panel. Ql-Q3 are all mounted in similar fashion. Interference suppression coil L1 is in the foreground and is secured to the PCB by a loop of tinned copper wire (near bottom of photo). Space the windings evenly around the circumference of the toroid and clean and tin the ends of the leads before soldering them to the PCB. The toroid can then be anchored to the PCB using a U-shaped loop of 1mm tinned copper wire which is soldered to the two adjacent pads. Triac mounting You are now ready to mount the Triacs. When the PCB is finally installed in the case, the Triacs are bolted to the rear panel for heatsinking. This means that the Triac leads must be cranked so that the rear mounting surface of the Triac is vertical and parallel with the edge of the PCB (see photo). The PCB assembly can now completed by installing the power transformer. This should be oriented with the secondary winding leads towards the centre of the board. Terminate the secondary leads on the two adjacent PC stakes as shown. Mounting the PCB Before mounting the PCB in the case, it is first necessary to connect all the leads for the mains active wiring. There are five leads in all: four 80mm-long leads at the rear of the board which later connect to the mains sockets; and one 160mmlong lead at location 7 which goes to the fuse. All these leads must be run using 240VAC cable and must be soldered directly to the PCB. You can now position the PCB in the case and secure it to the inAUGUST 1988 43 Most of the parts are mounted on a single large printed circuit board. Lace up the low-voltage and 240V AC mains wiring using cable ties as shown and sleeve all mains connections to the switch and fuseholder with heatshrink tubing. tegral plastic standoffs using selftapping screws. When this has been done, the various items of hardware can be mounted oil the front and rear panels. If you've purchased a complete kit, the front and rear panels will probably be supplied pre-punched. For those starting from scratch, the front panel artwork can be used as a drilling guide while Fig.5 shows the rear panel drilling details. Note that it is necessary to bolt the Triacs to the rear panel before mounting the mains sockets. This is because two of the mounting screws are actually covered by the socket bodies. Smear the mating surfaces of the Triac tabs with heatsink compound before securing them to the rear panel. 44 SILICON CHIP The rear panel slides into the second set of slots in the case rather than into the rear-most slot. This brings the rear panel nearer to the edge of the PCB and also reduces the overall depth of the completed instrument. As seen on Fig.4, two earth lugs are bolted to the rear panel at top left. In most instances, it will be necessary to scrape away the anodising around the mounting hole to ensure proper electrical contact. Internal wiring Take great care with the mains wiring as your personal safety depends on it. Fig.4 shows the mains wiring details. The mains cord enters through a hole in the rear panel and should be fed into the case until it reaches the front panel. Remove about 120mm of the outer sheath, then clamp the cord to the rear panel using a cord-grip grommet. The mains wiring to the fuseholder, switch and rear-panel sockets can now be completed. Be sure to use 240VAC cable for all this wiring - brown for active, blue for neutral and green/yellow for the earth wiring. Fig.4 (right): mount all the parts on the PCB as shown on this diagram. You can use ribbon cable for all the low voltage wiring but be sure to use 240VAC cable for the wiring to the mains switch, fuseholder, transformer and to the mains outlet sockets. Note that the circuitry at the back of the chassis operates at mains potential. 0 0 0 A Q MAINS SOCKET Q _ CHANNEL 2 MAINS SOCKET E si~~E\ I'I \., E 0 CHANN~L 1 Q E 0 0 MAINS CORO NE TRAL (BLUE) ACTIVE (BROWN) POWER TRANSFORMER RATE VR6 SENSmVITY VR5 VrrlJJ ~;;- p/27 25 ~26 S1 ,(\; d;,s g '-!.:; ✓ ,,119 S3 AUGUST 1988 45 I ~ ::1. 41 41 - I . 15 ~4.51 . 41 , , 14.5t 41 ~ -$-8--$-8 $!I ~ I ♦B 1 ¥ ~ ♦A "' -¥ .., ,...._ I I• 53 I I• I 52 N I 52 22 I HOLES: A : TRIAC MOUNTING B: HPM CAT35 MAINS SOCKETS (HOLES FOR WIRING NOT SHOWN) C : EARTH LUG D : CORD GRIP GROMMET Fig.5: this drilling diagram for the rear panel shows the mounting holes for the mains sockets, the Triacs, the earth lugs and the cordgrip grommet. Not shown are the holes for the speaker socket panel and the holes for the Active, Neutral and Earth leads to the mains sockets. Sleeve all exposed connections to the fuse and switch with heatshrink tubing to prevent accidental contact. This step is absolutely imperative. If you leave them exposed, it is highly likely that you will get an electric shock later on. Although not shown on the prototype, all the leads to the rear panel sockets should pass through small rubber grommets. Don't leave these out - the insulation on the leads must be protected from the metal edge around each hole. Once the mains wiring has been completed, it must be laced together with cable ties as shown in the photographs. This will prevent any of the wires operating at mains potential from coming into contact with low voltage circuitry, if a wire happens to come adrift. The remainder of the wiring to the pots, miniature toggle switches, LEDs and speaker terminals can be run using rainbow cable or light duty hookup wire. This wiring must also be laced to prevent accidental contact with mains wiring if a wire breaks. Testing Before switching on, go over your wiring carefully and check for possible errors. Note that the circuitry on the output side of the MOC3021 optocouplers operates at mains potential, so don't go poking around here indiscriminately. These components include the 46 SILICON CHIP Triacs (Ql-Q4), coils Ll-14, the associated 6800 resistors and O.lµF capacitors, the MOC3021 optocouplers, and the mains sockets. The rest of the circuit operates at low voltage potential ( ± 12V) and is safe to work on provided the mains wiring to the switch and power transformer has been correctly installed and insulated. Once you are satisfied that the wiring is correct, apply power and check for + 12V at the output of the 7812 3-terminal regulator and - 12V at the output of the 7912 3-terminal regulator. If these Warning! Part of the circuitry in the Discolight is directly powered from the 240VAC mains so take care when working on this project. Those components on the PCB which operate at mains potential are as follows: the MOC3021 optocouplers, the Triacs (01 -04), coils L1-L4, the associated 6800 resistors and 0.1 µF capacitors, and the mains sockets. Before working on the lowvoltage circuitry, it is a good idea to disconnect the mains supply to these components. To do this, disconnect the Active lead (lead 7) at the fuseholder and the Neutral lead (lead 5) at the mains switch. voltages are incorrect, switch off immediately and check for power supply wiring errors. Assuming that the voltages are correct, you should also check the voltages on the supply pins of the ICs. Once again, switch off and check for wiring errors should anything be amiss here. If everything checks out OK, then the chances are your Discolight is working perfectly. Here's how to test the unit: e Set the BEAT switch to Oscillator, the DISPLAY switch to Unmodulated and the RATE control to mid-position. The four frontpanel LEDs should now operate according to the pattern selected by the PATTERN switch (ie, Chaser, Strobe or Alternate). • Set the PATTERN switch to Chaser mode and check that the DIRECTION switch provides Forward, Reverse and Automatic operation. Note that when the DIRECTION switch is set to Automatic, the display should automatically reverse direction every minute or so. • Set the BEAT switch to Music, the SOURCE switch to Microphone and the SENSITIVITY control to maximum. This now sets the pattern rate to the beat of the music and this can be simulated by tapping on the top of the case. e Set the DISPLAY switch to 4-Band Modulated. You should now ro .7 0 0 0 a0 0 /; 0 0 - I D~ - ~ o o :,: L!:2::= ~ ~~=:::::::.____.K.~ Fig.6: you can use this full-size pattern to etch your own printed circuit board. Alternatively, you can buy a ready made PCB as part of a kit or from one of the suppliers listed on page 96 of this issue. Carefully inspect the board for defects before installing any of the components. AUGUST 1988 47 r CHANNEL 4 CHANNEL 3 0 0 MICROPHONE MUSIC 4 BAND MODULATED 0 0 SPEAKER OSCILLATOR UNMODULATED J SOURCE BEAT DISPLAY DISCOLIGHT • POWER • RATE SENSITIVITY I\ I\ [MOD- LFUSE10A Fig.7: this full-size artwork can be used as a drilling template for the front panel. get a variable brightness display, according to volume and frequency. Note that you will either have to whistle or play music to get the midtreble and upper-treble bands to operate. • Set the DISPLAY switch to Modulated mode and the BEAT switch to Oscillator. The display brightness of the pattern, as selected by the PATTERN switch, should now vary according to the music volume. • Set the DISPLAY switch to 4-Band Modulated, set trimpots VR1-VR4 to maximum (ie, fully clockwise as seen from the front of each trimpot), and connect 240V coloured lamps to the mains outlets. Now play some music and adjust the SENSITIVITY control so that the dimmest lamp is driven to mid brightness. The trimpots for the other three channels should now be wound back to give equal brightness on all four channels. Troubleshooting Provided that you've followed the wiring diagrams carefully, your Discolight should work first time. If you do run into problems, the most likely causes are broken PC tracks, missed solder joints or solder bridges between IC pins. Wiring errors and incorrect component orientation are other common problems with projects that don't work. Before working on the circuit 48 SILICON CHIP though, it is a good idea to disconnect the mains wiring to the Triacs and mains outlets sockets. To do this, disconnect the active lead (lead 7) at the fuseholder and disconnect the neutral lead (lead 5) at the mains switch. This will make the circuit safer to work on when you are troubleshooting the low voltage circuitry. Despite the circuit complexity, the Discolight is quite easy to troubleshoot if you do run into problems. The block diagram (Fig.1) published on page 57 of the July issue should be particularly useful here. Let's look at some typical situations: Symptom: front panel LEDs all work OK but one of the 240V lamps fails to operate. Check: the Triac and associated circuitry between the MOC3021 and the mains socket in that channel (make sure that the lamp itself is OK). Symptom: one channel fails to operate when the DISPLAY switch is set to 4-Band Modulated. Check: filter circuit, rectifier and comparator for that channel (ie, IC2, D1-D4 and IC3). Note that the output of each op amp filter stage (IC2a-lC2d) should be very close to 0V DC. Under no-signal conditions, the outputs of the comparator stages (IC3a-lC3d) should all be low. Symptom: unit works when the SOURCE switch is in Speaker posi- tion but not in Microphone position. Check: the electret microphone and the circuitry associated with op amp IC1 b. There should be 6-BV across the electret microphone. Symptom: unit works only when the DISPLAY switch is set to Unmodulated mode and the BEAT switch is set to Oscillator. No channels light for other settings of the DISPLAy switch. Check: wiring to SOURCE switch S1, SENSITIVITY control VR5 and the circuitry associated with ICla. Symptom: lights do not chase or strobe when BEAT switch set to Oscillator. Check: circuit associated with ICld. Note that the output of ICld should oscillate between + 12V and -12V at a frequency determined by the setting of the RATE control. You can check for correct operation by monitoring the output of ICld with an analog multimeter. If everything is OK at this point, use your multimeter to check that outputs Ql and Q2 (pins 6 and 11) of IC6 are also oscillating (between 0V and + 12V). If there is no signal here, the fault is in the vicinity of IC5 and IC6. Symptom: the pattern fails to automatically reverse after every minute or so when the DIRECTION switch is set to Automatic. Check: the wiring to the DIRECTION switch and the circuitry associated with IC4a. Use your multimeter to check that the output of IC4a swit- I STRI CHANNEL 2 0 0 -CHASER DBE- Back Issues CHANNE777 FORWARD REVERSE-0 I ~ALTERNATE AUTOMATIC PATTERN Issue Highlights ches high and low at about one minute intervals as the 100µF capacitor charges and discharges. Symptom: lamps stay on in both 4-Band Modulated and Modulated mode. Check: that the ramp voltage from IC4d does not remain low all the time. If you check the output of IC4d (pin 14) with a multimeter, you should get a reading of about 2.8V. If the voltage is close to 0V, check the ramp signal circuitry associated with IC4b, IC4c and IC4d. The ramp signal circuit is best checked using a CRO to verify the waveforms shown on the circuit diagram (Fig.3). If you don't have a CRO, then the best procedure is to measure the average DC voltage on the op amp and Schmitt trigger outputs. You should find + 5.3V on the output of IC4b, + 6V on pins 2 and 4 of IC9a and IC9b respectively, + 0.9V on pin 1 of IC4c and on pin 6 of IC9c, and 2.8V on pin 12 of IC4d. 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. Footnote: 10 small plastic cable ties and 12 small rubber grommets should be added to the parts list published last month. Also, the four 10kn pullup resistors at the outputs of the IC3 op amps, as shown on the circuit diagram (Fig.3), are not necessary and have been omitted from the PCB. ~ November 1987: Car Stereo in Your Home; 1GHz Frequency Meter; Capacitance Adapter for DMMs. December 1987: 100W Power Amplifier Module; Passive lnfrared Sensor for Burglar Alarms; Universal Speed Control and Lamp Dimmer; 24 V to 1 2V DC Converter February 1988: 200 Watt Stereo Power Amplifier; Deluxe Car Burglar Alarm; End of File Indicator for Modems; Simple Door Minder; Low Ohms Adapter for Multimeters. March 1988: Remote Switch for Car Alarms; Telephone Line Grabber; Low Cost Function Generator. April 1988: Walkaround Throttle for Model Railroads; pH Meter for Swimming Pools; Slave Flash Trigger; Mobile Antennas for the VHF and UHF Bands. May 1988: Optical Tachometer for Aeromodellers; High Energy Ignition for Cars; Ultrasonic Car Burglar Alarm; Restoring Vintage Radio Receivers. June 1988: Stereo Control Preamplifier; Breakerless Ignition For Cars; Automatic Light Controller; Mega-Fast Nicad Battery Charger. July 1988: Fitting a Fuel Cut-Off Solenoid; Booster for TV & FM Signals; The Discolight Light Show; Tone Burst Source for Amplifier Testing. Price: $5.00 each (incl. p&p). Fill out the coupon below (or a photostat copy or letter) and send it to: SILICON CHIP, PO Box 139, Collaroy Beach, NSW 2097. Please send me a back issue for □ November 1987 □ December 1987 tJ dtt11t10F'f 1 QiS. (Sold Out) □ February 1 988 □ March 1 988 D April 1 988 D May 1 988 □ June 1 988 □ July 1 988 Enclosed is my cheque or money order for $ ..... ... or please debit my □ Bankcard □ Visa Card Name .. .......... .... ....................... .. .... .. ............................ .......... ...... . Address .. ....................... ... ...... ..... .... ............... .... ........... ........ ...... . I Suburb/town .................. ............. .... ..... .. .......... Postcode .. ... ......... . . ; Card No .... .. ..... .. ... ..................... ... ........ ...... ... .. ...... .... .......... ....... .. . ____________ . --------------~ I,..... Signature ... ..... ..... ..... ...... .. ... ... ..... .... Card expiry date .. .... ./ .... .. ./ ...... . ' AUGUST 1988 49