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=fillflJIIIIJI/ flJll/!1- - PART 2 Last month, we introduced our new 4-Channel Dimmer and gave the circuit and operating details. This month, we show you how to build it and list a brief troubleshooting procedure. By JOHN CLARKE Building the SILICON CHIP 4-Channel Dimmer is a straightforward job although it must be done exactly to .our instructions. Part of the circuitry in this device is powered directly from the mains and therefore must be regarded as potentially dangerous. That's not to say that the dimmer is dangerous to use; it's not. The wiring all conforms to the relevant safety regulations and you will have no problems provided you follow the three wiring diagrams to the letter. OK, with that out of the way, let's get down to the construction details. As shown in the photographs, the project is built into a metal case with a sloping front panel. All the operating controls are mounted on this front panel, while the four mains sockets are mounted in a row on the rear panel of the unit. Inside the case, most of the parts are mounted on two PC boards. The main board is coded SC10106911 (201 x 158mm) and is mounted on standoffs on the bottom of the case. It holds most of the parts, including the four toroids and the insulated-tab Triacs. The second board accommodates the six pushbutton switches and is mounted on the lid of the case, along with the slider pots and the power switch. This board is coded SC10106912 and measures 160 x 67mm. To simplify the wiring, the two boards are connected together via two cable assemblies which plug into 8way header pins. These allow the case to be opened up to provide access for servicing, should it ever be needed . We envisage that readers will be constructing the 4-Channel Dimmer from a kit. This is because the metal case is not a standard unit and requires numerous cutouts for the slider pots and switches. However, there's nothing to stop you from making your own metalwork if you already have most of the parts. By the way, at least two retailers will be supplying kits for this project. Both have indicated that the metalwork will be supplied fully punched, with screen printed labelling on the front panel. Board assembly The switch PC board carries the six pushbutton switches, the two right-angle pin headers & a few wire links. There are also four PC stakes, to terminate external connections from the sliders. The LEDs are part of the switches. 68 SILICON CHIP Before starting construction, check the two PC boards carefully for manufacturing defects. You can do this by comparing them with the published patterns. Check the hole sizes in the boards as well. The corner mounting holes on both PCBs should be 4mm diameter, as should the four ·mounting locations for the toroids. The smaller switch board can be assembled first - see Fig.7. Begin by running in the same direction, as this makes it easier to check the board later on. Take care to ensure that all the ICs are oriented correctly (note: IC3 faces in the opposite direction to the others) . Similarly, take care with the orientation of the diodes and be sure to use the correct device at each location. The type numbers can be checked from the parts list published in Pt.1. In particular, note that ZD1 is a 10V 1W zener diode. Now install the capacitors, transistors, 3-terminal regulator (7812), trimpots and the two 8-pin headers. Note that two different transistor types are used. The parts list again shows the type numbers while the circuit diagram (Fig.3) shows the device pinouts. Install the 3-terminal regulator with its metal tab towards the adjacent 2.2kQ resistor. Toroids To make construction easy, it's best to purchase a complete kit with a screen printed front panel & pre-punched metalwork. Be sure to follow the wiring diagrams exactly, as some of the circuitry operates at mains potential. l 1 1 • 1 l 1-LED47 A--(}-K TO WIPER VR1 TO WIPER VR2 IQ l TO WIPER VR3 TO WIPER VR4 Fig.7: parts layout for. the switch PC board. The parts labelled "A" & "B" are the two right angle pin headers. Install them with their pins facing outwards. installing PC stakes at the four external wiring points, then solder in the wire links. A worthwhile tip here is to stretch the link wire slightly between two sets of pliers before installation, so that the wire is nice and straight. Once the links are in, the six plastic switches can be installed. Be sure to push the switches all the way down so that their diagonally-opposed plastic locating pins fit into the holes in the board. Finally, solder in the two right angle pin headers, with the pins facing outwards. The main PC board can be tackled now. Fig.8 shows the parts layout for this board. As before, start by installing the PC stakes and wire links. PC stakes are used to terminate the Triacs and at all external wiring points except for the Active input from the mairis terminal block. Do not install the three wire links shown immediately behind the toroids (L1-L4) at this stage. These links are at Active mains potential and are installed later, using mains-rated insulated cable. Next, install the resistors, diodes and ICs. It's a good idea to install the resistors with their colour codes all The toroids are wound using 18 turns of 0.8mm enamelled copper wire (ECW). First, cut the 4-metre length of wire supplied into four 1metre lengths, then straighten each wire by stretching it slightly. This done, wind each toroid in turn by first passing 500mm of wire through its centre and winding on nine turns. The remaining nine turns are then wound using the other end of the wire , to make up the required 18 turns. Once all four toroids have been wound, they can be installed on the PC board. To do this, feed the leads through the appropriate holes, strip away the enamel and solder them to the board. The toroids are then secured on the board using a screw, plastic washer and nut. You can use transistor insulating bushes for the washers. The three mains-Active links immediately behind the toroids can now be installed. Use mains-rated cable for this job and solder the leads directly to the board . The Active input lead is also soldered directly to the board and.should be left about 100mm long for ultimate connection to the mains terminal block. Triac installation The four Triacs are bolted to the bottom of the case with their leads bent up and across to fit over the PC stakes on the board - see Fig.9. First, bend each lead upwards at right an]UL Y 1991 69 CH2 CH1 CH3 ACTIVE ACTIVE 1 ACTIVE ·TRIAC3 IAC2 •G oi. I .r:i'ill!/~ IC2 M33 ---c::>--t' 07 Fig.8: the parts layout for the main PC board. The type numbers & pinouts for the semiconductors are shown on the main circuit diagram & in the parts list (see Pt.1). Take care with component orientation & note that the three links behind toroids L2, L3 & L4 must be run using insulated mains cable. gles exactly 3mm from the Triac body. This is best done by using long-nose pliers to hold the lead close to the Triac body and then pushing the lead upwards. Once the leads have all been bent, the Triacs can be temporarily bolted in position and the PC board secured on 6mm standoffs. This done, mark the Triac leads where they intersect the top surface of the board, then remove the Triacs and bend the leads at right angles again. Finally, check that each Triac can now be slid over its PC stakes and that the hole in its metal tab lines up with the hole in the case. Note that the hole in the gate lead of each Triac is narrower than the others. This means that the corresponding PC stakes will have to be narrowed by squeezing them with 70 SILICON CHIP pliers until the gate leads fit. The metal tabs of the Triacs can now be smeared with heatsink compound and the Triacs permanently bolted to the case. Note that because insulated-tab Triacs are specified, no insulating bushes or mica washers are necessary. Solder all the Triac leads, then trim the ends of the PC stakes to reduce the possibility of accidental contact. Once the Triacs are in position, the power transformer, mains terminal block and earth lug can be installed. If the case has been anodised, scrape away the anodising from around the earth lug mounting holes to ensure a good electrical contact. Front panel At this stage, you can start mount- ing the various items of hardware on the case lid. Begin by installing the eight slider pots. These are mounted on the 9mm spacers which are attached to the pots using the 3mm grub screws supplied. To attach a spacer, first screw the grub screw about halfway into the slider pot hole, then screw the spacer onto the remainder of the grub screw and tighten. A problem that sometimes arises here is that the grub screw continues to turn in the slider pot when you attempt to screw the spacer on. If this happens, the thn,ad of the grub screw can be slightly damaged over half its length using pliers and this damaged end then screwed into the pot. This should create sufficient friction to prevent the grub screw from turning when the spacer is screwed on. After all the spacers have been installed, the pots can be secured to the front panel using the 3mm countersunk dress screws. Note that the pots ' ·-~f, ,~ . The main PC board is secured to the bottom of the case on 6mm standoffs, along with the power transformer & mains terminal block. Note that the circuitry behind the MOC3021 optoisolators operates at mains potential. This includes the MOC3021s themselves, plus the toroids, 680Q resistors & 0.22µF capacitors. can be mounted either way around , although it's best to orient them all the same way for the sake of consistency. Next, install the knobs and check that they all slide up and down without fouling the slots in the case. Before mounting the switch board, the four leads that go to the wipers of VR1-VR4 must be soldered to the PC stakes. Use a 10cm length of 4-way rainbow cable for this job. This done, the switch board can be attach ed to four 9mm spacers which are secured to the front panel using countersunk dress screws. Note that an insulating washer must be installed under the mounting screw The switch PC board & the eight slider pots are all mounted on the case lid on 9mm spacers. An insulating washer must be installed under the board mounting screw at lower left to prevent it shorting out the adjacent copper tracks. JULY 1991 71 This close-up view shows how the Triacs are mounted, with their leads bent up & across so that they fit over the PC stakes soldered to the main PC board. Because insulated-tab devices are specified, the Triacs are bolted directly to the case without insulating hardware. adjacent to VR8, to prevent it shorting out adjacent PC tracks. Now check that all the switches operate freely. If they don't, you can reposition the PC board by slightly enlarging its mounting holes. The remaining items of hardware Mains wiring CAPACITOR CODES D D D D D D except for the mains sockets can now be installed in the case. These include power switch S7, the rubber grommets, the fuseholder and the earth lugs. The cord grip grommet can also be used to anchor the mains cord at this stage. Be sure to leave sufficient mains cord inside the case to reach power switch S7 (about 10cm). Value IEC Code EIA Code 0.22µF 0.1µF .039µF .01µF .001µF 220n 100n 39n 10n 1n 224 104 393 103 102 Fig. 9 shows the chassis wiring details. Note that you must use mainsrated cable for all wiring to the mains sockets, mains terminal block, fuse , power switch and earth lugs. To conform to the relevant standards, use brown wire for the Active connections, blue wire for the Neutral con- nections, and green/yellow wire for the earth connections. Do not use the green/yellow wire for anything other than the earth wiring. If you do, it could create an extremely hazardous situation for someone else should the unit require servicing later on. Begin the mains wiring by installing the wiring to the Neutral and Earth terminals of the mains sockets. These terminals are connected together in daisy chain fashion, with the :various leads passing through rubb er grommets. Twist the ends of the leads together before attaching them to the mains sockets and don 't leave out the grommets - they are vital safety components. Four 130mm-long leads can now be connected to the Active terminals of the sockets, and the Neutral and Earth leads connected to the righthand socket (as shown in Fig.9). The Neutral lead can initially be made about 150mm long. Once this has been done, the mains sockets can be bolted to the rear panel. The mains wiring is now completed with the lid of the case sitting upright on the mains sockets, .immediately behind the bottom of the case. Use plastic cable ties to lace the wiring together as shown in the photographs. By the way, it's a good idea :o unbolt the earth lugs when solde,mg leads to them. If they are left in situ, the case acts as a heatsink and you will find it difficult to make a good solder joint. The power switch (S7) and fuseholder should both be sleeved with heatshrink tubing to prevent accidental contact with the mains. This means that you have to push heatshrink tub- RESISTOR COLOUR CODES D D D D D D D D D D D D 72 No. Value 4-Band Code (5%) 5-Band Code (1%) 4 3 2 470kQ 100kQ 47kQ 22kQ 10kQ 5.6kQ 3.3kQ 2.2kQ 1kQ 680Q 220Q yellow violet yellow gold brown black yellow gold yellow violet orange gold red red orange gold brown black orange gold green blue red gold orange orange red gold red red red gold brown black red gold blue grey brown gold red red brown gold yellow violet black orange brown brown black black orange brown yellow violet black Dd brown red red black red brown brown black black red brown green blue black brown brown orange orange black brown brown red red black brown brown brown black black brown brown blue grey black black brown red red black black brown 11 4 1 4 7 8 SILICON CHIP ing over the wiring leads before they are soldered to their respective terminals. The heatshrink tubing is then pushed over the body of the component and shrunk using a hot air gun. Do not connect the mains input lead from the PC board to the terminal block at this stage. Instead, tape the end of the lead down out of the way so that it cannot possibly short anything out. That way, the low voltage circuitry can be safely tested before the Triac section of the circuit is connected to the mains. Low-voltage wiring <at> , SWITCH PCB I I I I C D t( VRB VA) I I I I I I I I I I I I I I I {( , , ' I I I P1• I <ID -1 • I I r;;-1• K The low-voltage wiring is straightforward. Begin by connecting the leads from the switch PC board to the pot wipers , then link the relevant pdt terminals together using tinned copper wire. This done, the leads between the pots and the main PC board can be run using rainbow cable. Route the cable so that it runs down the lefthand side of the case as shown in the photos. The two sets of 8-way pin headers (A and B) are also wired using rainbow cable. Two identical cables, each about 25cm long, are required and these are terminated at both ends using 8-way header sockets. To do this, first strip back the ends of the wires and crimp the header pins to them using pliers. The connections are then soldered, the crimp lugs bent over the lead insulation and the ends pushed into the socket shells using a small screwdriver until they click into place. Make sure that you plug the cables in the correct way around, as shown in Fig.9. The "1" side of the A socket on the main board must connect to the "1 " side of the A socket on the switch board and similarly for the B cable. VR2 VR3 VR4 I L G VR1 , VR5 VR6 :- • I ~ REAR MAIN PCB Test & adjustment Before applying power to the unit , carefully check all wiring and the PC boards for correct parts placement. In particular, check the mains wiring to ensure that the unit is safe and check that there are no shorts between mains Active and the chassis. If everything is OK, apply power and check the supply voltages on the ICs. To do this, clip the negative lead of your multimeter to the metal tab of the 7812 regulator (note: the circuit earth is not connected to the case) E• Do •H •G BASE Fig.9: here are the chassis wiring details. Note that all wiring to the mains sockets, mains terminal block, fuseholder, power switch (S7) & earth lugs must be run using mains-rated cable. Do not connect the Active lead from the main PC board to the mains terminal block until the low voltage circuitry has been tested, as described in the text. ]ULY 1991 73 ff 0 and measure the voltage at pin 4 of !Cl; pin 3 ofICZ & IC3; pin 14 ofIC4, IC6 & IC7; and pin 16 of IC5 & IC8. These pins should all be at +12V. If the voltage measured is not between +11.5V and +12.5V, switch off immediately and check that the !Cs and regulator are all correctly oriented. 74 SILICON CHIP If these are OK, check the board for shorts or open circuit tracks. Assuming everything is OK, the 10V supply for the Channel Master, Flash Master and Chaser Master controls can now be set. Connect your multimeter between the tab of the 7812 regulator and the top of the master controls (VR5 , VR6 & VR7) ; ie, to point G. Adjust VR9 for a meter reading of +lOV. The unit is now ready for an operational test but first switch off and fit the lid to the case. To check the unit , just following these step-by-step instructions: (1). Set all the sliders to minimum and apply power. Initially, the Chaser LED should be off. Push the Channel Master control fully upwards and check that the channel LEDs light (and increase in brilliance) when the Channel Level controls are advanced. Check that the Channel Master pot controls the overall brightness of the channels. (2). Set the Channel Master control to minimum and press the Channel Flash switches. Check that the channel LEDs light to the brightness set by the Flash Master control. (3). Press the Chaser switch and check that the Chaser LED lights. The Single Step LED should flash at the rate set by the Chaser Rate control. Check that the Channel LEDs chase at the rate set by the Chaser Rate control and that their brightness can be varied by the Chaser Master control. (4). Set the Chaser Rate control to minimum. Check that the Single Step LED goes out and that the chaser action stops. Now check that the Single Step control can be used to step through the chase sequence. The Single Step LED should light each time this switch is pressed. (5). Press the Chaser switch again and check that the chaser operation halts and that the Chaser LED goes out. Preheat setting Assuming everything checks out so far, switch off the unit and pull the plug from the mains outlet. Now open the case again and connect the Active lead from the main PC board to the Use plastic cable ties to lace the wiring at several points to ensure that everything it kept neat & tidy. Pay particular attention to the mains wiring & use your multimeter to check that there are no shorts between mains Active and the case before switching on. Also, check that the earth lugs make good electrical contact with the case (scrape away the anodising if necessary). rJ .. 0 6 1 SC 10106912 0 o_j Fig.11: this is the full-size artwork for the switch PC board. ]ULY 1991 75 The 4-Channel Dimmer can control anything from 40W light bulbs to high power spotlights like those shown here. Note that although each channel can control a load of up to 2400W, the maximum lamp load for the unit is 3600W. terminal block. When this has been done, the preheat setting can be adjusted as follows: (1). Connect a light to one of the channels of (eg, a 100W light bulb or 500W spotlight). Apply power and check that its brightness can be controlled using the Channel Master control and the re levant Channel Level control. (2). Set the Channel Master control to minimum and adjust VR10 so that the lamp just glows a dull orange. This is the setting for the filament preheat voltage. The 4-Channel Dimmer is now ready for use. Disconnect power (ie, pull the plug from the wall socket) and secure the lid to the case with self-tapping screws. If it doesn't work The fuseholder & the power switch are sleeved with heatshrink tubing to guard against accidental contact with the mains. Use a hairdryer to shrink the tubing over these components. 76 SILICON CHIP Most project problems are caused by faulty soldering, incorrect component placement and wiring faults. If you run into problems, check these three things first. In particular, try to isolate the fault to a specific part of the circuit and then relate this to the PC boards. Often, a visual inspection is not enough to detect a problem and running a sharp knife between suspect tracks can sometimes eliminate a short circuit. For more specific problems, check the following troubleshooting guide. (1) . Power switch neon does not light and power does not come on: check fuse and switch wiring. (2) . Fuse blown: check wiring to switch , fuse, terminal block and mains sockets. (3). Switch S1-S6 controls not operating correctly: check the A and B cable connections between the two PC boards for polarity and for possible cross connection. (4). Chaser LED switches on but cannot be switched off when the Chaser Master control is at maximum: adjust VR9 to slightly reduce the 10V rail applied to the pots (or use an 11 V 1W zener diode for ZDl) . (5) Chaser Rate control not working: check the connections to VR8 and the resistor values around IC2b. (6). Channel LEDs do not light but some channels will drive lamps correctly: check Q5 and Q6 for correct type numbers (BC547) and check Q1Q4 (BC557). Also, check that the LEDs are correctly oriented in the switches. (7). Channel LEDs operate but not all channels drive lamps: check inductors L1-L4 for bad solder joints. (8). Chaser ON/OFF switch does not latch for Chaser operation: check that pin 13 of IC8 goes high when the switch is pressed, and then goes low again when the switch is released. Also, check that pin 12 is at ground (except when power is first applied to the circuit), and that pin 15 toggles between low and high each time the Chaser ON/OFF switch is pressed. (9). Channel LEDs and lamps fail to operate: use a CRO to check the ramp waveform at the output of !Cl b (pin 8). If no CRO is available, use your multimeter to check the average DC voltage at this point. You should get a reading of about 3.5V. If no ramp is present, check the circuit around ICl b andIC2a. SC