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Building our new Part II by John Clarke Trailing Edge Dimmer for modern mains-powered lighting Last month, we described how our new trailing edge dimmer can drive dimmable LEDs and compact fluorescent lamps, as well as incandescent and halogen lamps using suitable transformers, where an old-style leading-edge dimmer can not. It’s an elegant and modern-looking design which can be controlled using one or more touch panels, or a slimline infrared remote control. Now we move onto building it and wiring it up. I n the first article (February 2019 SILICON CHIP), we explained why you need a trailing edge dimmer to control modern LED lighting. Older dimmers used Triacs and this necessitated switching power to the lamp(s) on in the middle of a mains half-cycle and off at the zero crossing. But that’s no good for devices that use switchmode supplies, such as LEDs, CFLs and halogen lamps with electronic transformers. It generates very high current spikes that will quickly destroy the power supplies This trailing edge dimmer does not have that problem, and many modern lights are now designed to be dimmed by just this type of device. While we had an extensive explanation of leading vs trailing edge dimmers last month, we didn’t have room to show actual scope grabs of these dimmers in operation. Now we do, so you can refer to Scope1-Scope5. Scope1 shows an older style leading edge dimmer operating with an incandescent lamp load. Scope2 shows the same type of dimmer attempting to drive a dimmable LED. You can see that it doesn’t work very well! In contrast, screen grabs Scope3Scope5 show the waveforms applied to a dimmable LED lamp from a trailing edge dimmer. You can see that these waveforms are pretty clean and 76 Silicon Chip the lamp’s brightness varied as you would expect, from a low level when Scope3 was taken up to moderately high brightness for Scope5. So now that you know how this Dimmer works and you’ve read about all its great features, naturally you want to build one (or several). You can purchase the PCBs and hard-to-get parts from the SILICON CHIP ONLINE SHOP (see parts list last month), and the remaining parts from your usual component supplier(s). You can then begin to put the boards together, using the following instructions. Scope1: an incandescent lamp dimmed to half brightness using an old-fashioned leading-edge dimmer. You can see how the lamp voltage suddenly jumps from near zero up to the full ~325V DC mains peak voltage when the Triac turns on. That would cause a huge inrush current with a typical LED lamp which has a capacitor-input switchmode power supply. It would probably destroy the lamp in a short time; even if it didn’t, it would likely flash like a strobe. Scope2: here’s a LED lamp being powered from a leading-edge dimmer set near full brightness. This is an example of what not to do! You can see that even though the voltage steps are not quite as severe in this example as in Scope1, the lamp still “wigs out” during the second half-cycle, switching on and off rapidly and drawing high current pulses. Its electronics won’t last long operating under these conditions. Australia’s electronics magazine Is it legal to build? Before we get into it, note that while you can certainly build this dimmer yourself (and we’ve gone to quite a bit of effort to make it as simple as possible), in Australia it is not legal to wire siliconchip.com.au Please note: this is a 230V mains powered device. Do not construct this if you do not have mains experience! The three assembled PCBs used in this project. On the left is the main board which contains the PIC – which controls everything – along with the transformer (which you wind yourself) and the power Mosfets plus, of course, the connection terminal block (the opposite side of this PCB is not shown). In the middle is the mounting plate which maintains electrical isolation, while on the right is the optional dimmer extension (which you only require if you need extra touch plates). it up yourself. You will need a licensed electrician to do so. If you’re lucky enough to live in New Zealand, though, you can do your own household wiring legally so we have shown the appropriate wiring diagrams. Construction The dimmer is built on a PCB coded 10111191, measuring 66 x Scope3: this is how you should dim a LED lamp. In this case, it is being driven by a trailing-edge dimmer at a low brightness level. Here the lamp voltage smoothly ramps up from zero to just under 200V, then the transistor switches off power to the lamp until the start of the next half-cycle. The lamp detects the reduced duty cycle/ peak voltage and runs at reduced brightness. siliconchip.com.au 104mm. The PCB assembly mounts on a separate Backing Plate PCB coded 10111192 which measures 58.5 x 104mm and the whole assembly mounts within a Clipsal Classic blank plate, with a matching blank aluminium touch plate. The completed dimmer can be mounted to a metal wall box in a brick wall, but it must be spaced from the wall box using a mounting block of 30mm or deeper; otherwise, the circuit may make contact with the metal box, which would be a hazard. It can be mounted directly to a stud on a plasterboard wall using standard mounting hardware. Alternatively, it can be placed on a thin or standard depth surface-mounting box. Refer to the PCB overlay diagram, Fig.3, during assembly. Fig.4 shows what the more-or-less blank mount- Scope4: the same LED lamp being run from the same trailing-edge dimmer but with a slightly increased brightness level. The step that you can see is probably because the capacitors in the lamp’s switchmode supply remain charged after the transistor in the dimmer has switched off, and a small amount of voltage feeds back into the scope through the bridge rectifier. Scope5: here, the LED lamp is operating at around 75-80% of full brightness. You can see that the dimmer transistors remain switched on for more than half of each mains half-cycle. Comparing this to Scope2, it is obvious that a dimmable LED lamp operates in a much smoother manner with the trailing edge dimmer than it did with the traditional leading edge dimmer. Australia’s electronics magazine March 2019  77 Parts missing from the parts list last month 2 M3 x 15mm panhead machine screws 2 M3 nuts (for both the main and extension PCBs) 78 Silicon Chip 4004 4.7nF Fresnel lens: drill 9mm dia into CLIPSAL C2031VX blank plate Y 22k Hole for Touchplate Connection Do not drill when used with extension PCB Z 470nF X2 12V 470 Y 100nF SiHB15N60E 1.5M1W 470 EXTN 1 OPTO1 4N25 100nF 10k ZD2 1M (UNDER) A T1 2.2k IC1 12F617 Q1 X Q2 LAMP Z D2 N Link N-LAMP When no Neutral 47k 1M 4.7M 4 .7 M  VR37 SiHB15N60E (UNDER) D1 ZD1 47 1 W 100nF IRD1 IRD1 (UNDER) Trailing Edge Dimmer and Extension mounting plate C 2019 10111192 Rev.B * 470 1W ACTIVE, ing plate PCB looks like. For assembling the main PCB, start by fitting Mosfets Q1 and Q2. These are surface-mount devices which are soldered to the top side of the PCB. The substantial metal tabs need to be soldered using a hot soldering iron. It helps to spread a little flux paste on the tab pad before soldering the two smaller leads in place, then finish by soldering the tab. Make sure you heat the tab long enough for the solder to flow properly onto both the Mosfet tab and PCB pad, forming a nice, smooth fillet. You can then install the axial devices – ie, resistors, zener diodes and diodes. The Resistor Colour Codes table shows the codes but it is a good idea to use a digital multimeter to measure each value before soldering, just to make sure. (Many resistor colour bands can be mistaken, especially in low light). Note the specifically-called-for resistors in the table – the 4.7MΩ must 5.6V 100 F 4148 4 .7 M  VR37 WIRE SOLDERS (UNDER) UNDER PCB Rev.C 10111191 CON1 470 F C 2019 Trailing Edge Dimmer The second board (Fig.4, shown at right) does not have any components on it but has four nuts soldered to the top of the board to secure the main (or extension) PCB to. SHORT (~20mm) LENGTH TINNED COPPER WIRE TO CONNECT TOUCH PLATE + Fig.3: the PCB overlay diagram for the main Dimmer board, which you can use as a guide during construction. The infrared receiver IRD1 and three resistors (one 1MΩ Ω and two 4.7MΩ Ω) are mounted on the underside of the board (not shown separately). These resistors are mounted on the PCB surface (ie, not through holes), despite being axial leaded components. Mosfets Q1 & Q2 are SMDs and they are soldered to the top of the board. Also note the short length of tinned copper wire soldered to the underside of the PCB – it bends out 90° (ie, away from the PCB) to pass through the hole in the second board and thence through a hole drilled in the Clipsal mounting plate, to make contact with the touch plate. 470 1W EXTN LAMP, NEUTRAL TERMINALS TERMINALS* be the type shown and no codes are given for the 1W resistors in 5-band as these are very uncommon. Leave off the 4.7MΩ and 1MΩ resistors for now, as they are mounted on the underside of the PCB later. Diodes D1 and D2 can be easily distinguished as D2 is much smaller than D1 but ZD1 and ZD2 may look similar, so be careful to install the 5.6V and 12V zeners in the locations shown in Fig.3. Fit the microcontroller and opto- coupler next. Ideally, IC1 should be mounted using a socket, to make it easier to re-program if necessary, while OPTO1 should be soldered directly to the PCB. Be sure to orientate both correctly, with the pin 1 notch or dot located as shown in the overlay diagram, before soldering them. The capacitors can be installed now, starting with the smaller MKTs, then the larger X2 capacitor and finally, the electrolytic capacitors. Only the electrolytic capacitors Resistor Colour Codes     Qty. Value  2 4.7MΩ  1 1.5MΩ 1W  2 1MΩ  1 47kΩ  1 22kΩ  1 10kΩ  1 2.2kΩ  2 470Ω 1W  2 470Ω  1 47Ω 4-Band Code (1%) 5-Band Code (1%) yellow violet green brown (must be VR37 3.5kV safety resistors) brown green green brown (n/a) brown black green brown brown black black yellow brown yellow violet orange brown yellow violet black red brown red red orange brown red red black red brown brown black orange brown brown black black red brown red red red brown red red black brown brown yellow violet brown brown (n/a) yellow violet brown brown yellow violet black black brown yellow violet black brown yellow violet black gold brown For the Extension Board:  2 4.7MΩ yellow violet green brown (must be VR37 3.5kV safety resistors)  1 2.2MΩ red red green brown red red black yellow brown  1 1MΩ brown black green brown brown black black yellow brown  1 220Ω red red brown brown red red black black brown Australia’s electronics magazine siliconchip.com.au (100µF and 470µF) are polarised; their longer leads go into the pads marked with a + symbol in Fig.3 and on the PCB silkscreen printing. Next, mount the large four-way terminal barrier. Attach it to the PCB using two M3 panhead machine screws, approximately 20mm long, and two M3 hex nuts (which were not included in the parts list published last month). Once it’s securely fastened to the board, solder the four terminals using plenty of solder, to ensure reliable connections. Next, assuming you want infrared remote control, file the uppermost sharp corners of the infrared receiver plastic package so it fits inside the fresnel lens. The infrared receiver is mounted flat to the underside of the PCB with the lens located along the vertical centre line of the PCB. The PCB screen printing shows the correct mounting position. Bend its leads at right angles and feed them through the PCB pads, then solder them on the top side. If you do not want to use the infrared remote control option, instead you should fit a 1kΩ resistor between the outer two mounting pads for IRD1. Now attach two cable ties to the ferrite core and do them up tightly before cutting off the excess length, to ensure that the two windings stay separate. Next, cut a length of 16mm diameter heatshrink tubing that’s longer than the ferrite core is wide, slip it over the core with the primary winding exposed at one end and the secondary at the other, and shrink it down so it won’t move. Once you’ve done that, cut or punch some holes at the bottom to allow a cable tie to pass through. You can do this using a screwdriver but be careful not to damage the core or any of the windings when doing so. Winding transformer T1 Mounting T1 T1 is made up using a toroid ferrite core and windings made from 0.25mm diameter enamelled copper wire (ECW). The primary winding consists of 12 turns while the secondary has 48 turns, as shown in Fig.5. The primary and secondary are separate windings that are wound on opposite sides on the toroid, for isolation. Twist the two primary winding end wires together with a few turns and do the same to the secondary wire ends (this is not shown in Fig.5 for clarity). Cut off any excess wire length, ensuring there is enough left to reach the PCB pads, then use emery paper or a hobby knife to strip off the enamel insulation from the ends of each wire, so you can tin them. Make sure the solder takes properly to the wire. Feed a cable tie through the holes you made in the heatshrink tubing and then loop it through the 3mm holes in the PCB which are designed to hold the transformer in place. The square end of the cable tie should be kept on top of the PCB, on one side of the toroidal core. The PCB will not mount correctly if the end of the cable tie is on the underside of the PCB. Solder the two ends of the primary winding to the pads labelled W and X; it doesn’t matter which one goes to which. Similarly, solder the ends of the secondary to the pads labelled Y and Z. Now you can fit the three resistors that go on the underside of the board. The 1MΩ resistor has a hole for one of its leads and a pad for the other, but both are soldered on the bottom side OPEN END SECONDARY 48 TURNS OF 0.25mm ENAMELLED C OPPER W IRE SC 20 1 9 CABLE TIE siliconchip.com.au 16mm DIAMETER HEATSHRINK Can this dimmer be used with a standard lamp, etc? We’ve already been asked (!) . . . what if you have a lamp that’s normally plugged in (ie, such as a standard lamp, desk lamp, etc – one not “wired in” to the house wiring)? Is this dimmer suitable for these types of lamps? The beauty of this dimmer circuit is that it suits so many types of globes, (incandescent, dimmable LED, dimmable CFL, and so on) so in the vast majority of cases would be perfect. CABLE TIES AS BARRIERS OPEN END PRIMARY 12 TURNS OF 0.25mm ENAMELLED C OPPER W IRE PCB Of course, you would need to make absolutely certain that any box used was 100% insulated and, if metal, Earthed. The procedure we show in Fig.8 for testing the dimmer with an available Neutral is precisely how you would wire the dimmer for “plug in” use. If your lamp is currently being powered by a two core cable (ie, Active and Neutral) the cable should be replaced with a three-core (Active, Neutral and Earth). of the board. Make sure you trim the lead which pokes through the top side short after soldering it. Connection to the touch plate The soldering on the two Vishay 4.7MΩ VR37 series resistors is critical. Bend and cut their leads so that they sit flat on the provided circular pads and then solder them in place, surface-mount style. Make sure they are placed in the correct position and do not substitute anything else for these components. These resistors, chosen specifically for safety, are light blue in colour and are rated at 2.5kV RMS. They are fitted like this so that no connections are exposed on the top of the PCB. That fully isolates the resistor leads from the components on the top of the PCB. Also, it provides a high degree of voltage isolation between the touch plate connection and high voltage circuitry. The series resistors actually make contact with the touch plate via a short length (say about 20mm or so) of tinned copper wire. This is soldered to the top-most “pad” on the left side of the board. This wire is bent out at 90° to pass through the hole in the second (mounting plate) PCB thence through a tiny hole drilled to match in the Clipsal Plate. The easiest way to do this is to place the mounting plate in the Clipsal plate and drill a 0.9mm hole right through; ie, Fig.5: this diagram shows how transformer T1 is wound using 0.25mm diameter enamelled copper wire on a toroidal ferrite core. Once both windings have been made, fit two cable ties as barriers between them and cut the ends off, then slide heatshrink tubing over the transformer and shrink it down. Poke a hole through the tubing with a screwdriver and attach it to the PCB as shown before soldering the wires to the board. Australia’s electronics magazine March 2019  79 use the mounting plate as a template. When later assembled, the wire is bent back to be flush with the surface of the Clipsal plate so that when the aluminium touch plate is clipped into place, it makes intimate contact with the wire. (This wire is not soldered or otherwise fastened to the touch plate). Programming IC1 If you purchased a pre-programmed PIC microcontroller from the SILICON CHIP ONLINE SHOP, you can plug it into the socket now, after bending its leads to suit. Make sure its pin 1 dot is orientated as shown in Fig.3. If you have a blank PIC12F617 IC, you will need to download the firmware (HEX file) from our website, then load it into the chip using either a universal programmer or a PICkit 3 or PICkit 4 in-circuit serial program- Trailing Edge Dimmer Extension 4 .7 M  VR37 (UNDER) 10111193 Rev.C C 2019 3 9 1 1 1 1 0 1 1M 47nF Q3 220 CON2 SPARE Terminals Connected Together EXTN Fig.6, the Dimmer Extension PCB overlay, for when you want two or more dimmers controlling the same light or set of lights. There are just a few components on it, so it should be easy and quick to build as long as you are careful to fit them in the locations and with the orientations shown. Again, a short length of tinned copper wire bends down 90° to pass through the second (mounting) board, thence through the Clipsal mounting plate, to make contact with the touch plate. Mounting the board BC559 6 V8 D3 6 V8 2.2M ZD3 ZD4 4148 In our wiring diagrams, we have shown mains Active as RED and mains Neutral as BLACK. But didn’t wiring colours change to Brown (Active) and Blue (Neutral) quite some time ago? Yes they did . . . and theoretically, we should be showing the “approved” SAA wiring colours of Brown and Blue. However, even today you will find that the vast majority of electrical installations (ie fixed wiring) are done in the “old” colours of Red and Black. Because you are much more likely to find red and black wiring in your home, we have stuck with that you will likely encounter. TOUCH PLATE CONNECTING WIRE – BEND UP TO PASS THROUGH HOLE IN PCB AND CLIPSAL PLATE UNDERNEATH 4 4.7M .7 M  VR37 (UNDER) RED and BLACK . . . or BROWN and BLUE? ACTIVE mer (or similar) with a breakout board. Our PIC/AVR Programming Adaptor board from the May and June 2012 issues (siliconchip.com.au/Series/24) is suitable. If using a universal programmer, use the supplied software. For the PICkit 3 and PICkit 4, you can use the MPLAB IPE (integrated programming environment), part of the MPLAB IDE (integrated development environment), which is a free download from the Microchip website and is available for Windows, macOS and Linux. The backing plate PCB is sized to fit precisely into the Clipsal C2031VX blank plate. This then allows you to mount the main Dimmer PCB. Fit the backing plate into the Clipsal plate, noting that the screen printed side should be visible once you have finished; the PCB will only fit with one orientation. Mark out the centre for the hole required for the lens to fit into the Clipsal plate and note that this hole isn’t drilled when building the extension board, or if you have opted to leave out the infrared remote control feature. We have provided cross hair screen printing to show the centre position required on the backing plate. Drill the hole 9mm in diameter. The same sized hole needs to be drilled in the Aluminium plate. Drilling this out carefully against a block of timber; starting with a smaller diameter drill and reaming the hole out to 9mm will produce a better hole finish compared to using a 9mm drill bit. Also drill the 0.9mm hole for the touch plate connection wire now. This hole only is made in the Clipsal plastic plate, not the Aluminium plate. These three photos show the location and mounting of the touch plate connection wire. It passes through the mounting PCB and Clipsal plate to contact the cover when it is pushed on. 80 Silicon Chip Australia’s electronics magazine siliconchip.com.au Warning! Shock hazard Disconnect mains power at the switchboard before removing plate. Fig.7: this warning panel should be photocopied or printed and glued to the face of the Clipsal switch plate before the aluminium touchplate goes on top (make sure it doesn’t cover the wire which touches the aluminium touchplate). It’s a reminder to anyone taking the dimmer off the wall that there is live wiring and circuitry behind it. siliconchip.com.au ACTIVE ACTIVE LAMP NEUTRAL A EXTN SPARE (OR LOOP) Fig.8: here’s how to temporarily wire the Dimmer ALTERNATIVE EXTENSION for testing (or, (MOMENTARY indeed, for use MAIN CONTACT EXTENSION DIMMER with a plug-in MAINS-RATED SWITCH) lamp). Shown at top is the way to WHEN NEUTRAL IS AVAILABLE control a single lamp when you have both Active and Neutral available, while the lower diagram shows the connections when no Neutral is available. If you are not going to use an extension dimmer or push button, simply ignore those connections. SC 20 1 9 ACTIVE NEUTRAL LAMP MAIN DIMMER A EXTN SPARE (OR LOOP) Fit the backing plate PCB into the Clipsal plate and press it in so the PCB sits tightly inside. You can secure it with some silicone or polyurethane sealant, to ensure the PCB stays in place. To do this, apply a few dabs of the sealant to the underside of the PCB before inserting into the Clipsal blank plate. Insert the Fresnel lens, then align the dimmer PCB over the backing plate PCB and feed the touchplate wire through the backing plate hole and through the Clipsal blank plate hole. Then secure the dimmer PCB to the backing plate PCB using the M3 x 10mm screws. As you do this, ensure that the touchplate connecting wire is now protruding through the backing plate Since you’re probably going to have to pay an electrician to come around to your house and install the dimmer(s), you will want to be sure they are working first. The easiest safe way to do this is to use a surface GPO mounting block to suit the switchplate(s), screwed to piece of insulating material (eg, MDF) large enough to cover block. You will also need a mains extension cable cut in half to provide power to the circuit (from a power outlet) and a lamp (of the type you are using) to plug into the socket. Strip the outer and inner insulation of the ends of the cut mains cord and drill holes in the sides of the surface mounting block, just large enough for the mains cable to fit through. Go through the installation procedure in the main text of this article, ensuring that you conduct the safety checks as described. Use a double-screw BP connector to join the mains Earth wires in the two halves of the cable. The socket end of the mains cord will connect to your lamp load. Most dimmable LED lamps have a mains plug attached so you can simply plug it in. If using another type of lamp, you will need a suitable luminaire and a safe arrangement to connect it to a mains plug. In summary, if your final installation will include the mains Neutral wire, you can connect the Active wire from your mains plug lead to the “A” terminal on the Dimmer, the plug and socket lead Neutral wires to the “N” terminal (the terminal barrier used will easily accommodate two wires per terminal) and the socket Active wire to the “LAMP” terminal. If you will not have the mains Neutral available in your final installation, instead you will need to join the plug and socket lead Neutral wires together (again use a BP connector), the plug Active wire to the “A” terminal and the socket Active wire to the “N” and “LAMP” terminals as shown below. Make sure it is not plugged in while you connect it! Attach your surface mounting block to the MDF (etc) so that none of the mains wiring is exposed. You can then plug the lamp into the socket and the mains plug into a wall outlet and wait at least nine seconds (to skip the Calibration step, as explained in the text). You can then test that the touch and (if fitted) infrared remote control. If the lamp you’re using to test is the same one that will be used in your final installation, you can also complete the calibration procedure – see the steps below. It’s easier if you do it now, since it’s much easier to switch the dimmer on and off at this stage. N LAMP EXTN A Final assembly Testing before installation N LAMP EXTN A Remove the backing PCB and insert four M3 x 10mm screws in from the underside of the PCB at each corner mounting position and attach two M3 nuts to the top side. Tighten the first nut but leave the second nut only just touching the first nut. Solder the two nuts together and solder the lower nuts to the PCB. Once the solder joints are cool to the touch, remove the screws. Solder a 15-20mm length of tinned copper wire to the underside of the main dimmer PCB, at the end of the 4.7MΩ safety resistor. This is directly opposite the hole for the touchplate connection on the backing plate PCB. As with the safety resistors, this wire is surface-mounted to the bottom of the PCB. EXTENSION WHEN NEUTRAL IS NOT AVAILABLE Australia’s electronics magazine ALTERNATIVE EXTENSION (MOMENTARY CONTACT MAINS-RATED SWITCH) SC 20 1 9 March 2019  81 LAMP SOCKET LAMP SOCKET EARTH MAINS IN NEUTRAL N A E MAINS IN EARTH NEUTRAL N E A ACTIVE ACTIVE LOOPING “LOOPING” LOOPING “LOOPING” Fig.9b: replacing the light switch with the dimmer in the typical installation of Fig.9a is as simple as shown here: the Active wire DIMMER goes to the “A” terminal on the dimmer, while the “N” and “LAMP” terminals on the dimmer are joined and go back up to the Active terminal on the light fitting. Ensure you turn off the power at the switch board before installing the dimmer! PCB and the Clipsal blank plastic plate. Bend this wire over by 90° to sit against the face of the plate. This will contact the Aluminium plate when fitted, providing the touch sensing connection. Fig.7 is a safety warning label which you should print out and glue to the plastic plate. This is so that if the Aluminium plate is removed, the warning to switch off mains power at the switchboard will be seen. You can also download this label from the SILICON CHIP website for free as a PDF file, listed in the ONLINE SHOP under “Panels & Case Pieces”. As with the main Dimmer board itself, if mounting the extension board to a metal wall box (as used in a brick wall), it must be spaced from the metal box using a 30mm or deeper mounting block. Alternatively, it can be mounted directly to a stud (Gyprock) wall using standard mounting hardware or mounted on a thin or standard height surface-mounting box. Fig.6 is the PCB overlay diagram for the extension board. The resistors, zener diodes, the diode and transistor can be fitted where shown, in that order. The resistor colour code table shows the colours – note that some resistors will not normally be available in 1% types. It’s a good idea also to use a digital multimeter to measure each value. Note that the two 4.7MΩ resistors on the underside of the PCB are mounted later. The good news is that the two zener diodes, ZD3 and ZD4 are the same value, so you only need to watch the polarity of these two components, plus diode D3. The orientation of transistor Building the extension board You only need this board if you want more than one touch plate to control the same set of lights. The extension circuit is built on a PCB coded 10111193 which measures 58.5 x 104mm. You will also need a Backing Plate PCB (coded 10111192) to attach the extension board to the Clipsal blank plate, which once again is used with a blank aluminium faceplate. N LAMP EXTN A Fig.9a: this is a typical light switch wiring for a single light or fitting, with just a pair of wires (no neutral) coming down ON OFF from the light fitting on the ceiling to “LOOPING” the architrave switch. (N/C) One point to note is that the Earth ARCHITRAVE wire is often not used in manySWITCH older homes but in any case, the Earth plays no part in the dimmer design. The “looping” terminal is merely a handy not-connected termination point. LAMP SOCKET N E A Fig.9c: sometimes the Active and Neutral are wired to the architrave LOOPING switch with the switched “LOOPING” Active and the Neutral (N/C) going up to the lamp socket ACTIVE or fitting. MAINS IN The Earth ON OFF NEUTRAL (if connected) is often wired “LOOPING” directly to the ARCHITRAVE lamp socket. SWITCH 82 Silicon Chip LAMP SOCKET EARTH N E Fig.9d: here’s how to wire the “LOOPING” (N/C) dimmer in place of NEUTRAL MAINS the IN ACTIVE existing architrave switch when both Active and Neutral are available at the switch. This will DIMMER allow dimming from zero to 100%. N LAMP EXTN A EARTH Australia’s electronics magazine A Q3 also matters but it will be correct if you fit it with the flat face as shown. You will probably need to bend the leads slightly (eg, using small pliers) to fit the PCB pads. Solder the single capacitor in place next, then mount the screw terminals. As with the main board, attach the screw terminals using two 20mm M3 machine screws and nuts first before soldering the pins and use plenty of solder, to ensure good joints. The two Vishay 4.7MΩ VR37 resistors are surface-mounted on the bottom on the board in the same manner as for the main board. Once again, do not substitute these parts. They are high-voltage resistors that are rated at 2.5kV RMS and are specified for safety. They are light blue. Bend the resistor leads near the end of the resistor, then trim them so that they sit flat on the pads before soldering them. The procedure for attaching the extension PCB to the Clipsal plate using the backing plate PCB is the same as described for the main dimmer PCB. The exception is that you don’t drill the hole for the lens. Installation By now, you have tested the dimmer according to the procedure shown in the panel and diagrams of Fig.8. Use these, in conjunction with the diagrams of Fig.9 to show how installation is done in the two typical scenarios – no Neutral available (the more usual – Figs.9a and 9b) and the other possibility, Neutral available (Figs. 9c and 9d). No extension dimmer nor switches are shown in the Fig.9 diagrams; you’ll need to refer back to Fig.8 for their wiring. The dimmer and extension plates must be securely attached to a wall before mains power is connected. Of course, the power must be switched off at the fusebox or breaker panel while installing the unit. Before installing these units, carry out the following safety check. Switch your multimeter to its highest resistance measurement range and check the resistance between the Active terminal and the touchplate contact. Do this for both the main dimmer board and the extension board, if using an extension. The resistance should be close to 9.4MΩ. This verifies that the touchplate will not be hazardous. If you aleady have an older-style siliconchip.com.au dimmer that you’re replacing, (perhaps you want to change from incandescents to LEDs?) the new dimmer circuit is easily installed into because the wiring is the same, connecting to the incoming Active (brown or red) and lamp via the Neutral (blue or black) wires. This is shown at the bottom of Fig.8. This example includes one extension board plus a separate on/off momentary (mains-rated) pushbutton switch but these extra units are optional and can be omitted if not needed. If you are installing a new dimmer and you can run the incoming mains Neutral wire to the dimmer mounting location, that’s even better, as it will give you a full range of dimming from off all the way up to 100% (full brightness). As shown in Fig.8, the extension module requires an incoming Active connection and an extension wire which connects to the EXTN input on the dimmer. It can be installed into existing 2-way switch wiring, or you can have an electrician install new wiring if this is not already present. The unconnected loop terminals on the extension board can be used to terminate any extra wires that need to be joined. The momentary switch option, as shown in Fig.8, can be used in an architrave switch surround, making it easier for installation where space is limited such as in a door surround. Calibration If you were able to connect the incoming mains Neutral to the Dimmer siliconchip.com.au module, then there is no need to perform any calibration. It is initially set to provide the full incoming mains voltage to the lamp when switched on fully. If there is no separate Neutral wire available, the dimmer will get its supply power through the lamp. The dimmer will need to be adjusted to give the maximum lamp brightness without flickering. The adjustment needs to be started within nine seconds of power being applied to the dimmer. Otherwise, the dimmer will go into its normal operating mode. Powering up the dimmer involves switching on the light circuit at the electrical switchboard. As soon as you can and before nine seconds has elapsed, press and hold the touch plate continuously and wait until the light starts to increase in brightness. Remove your hand as soon as the lights start flickering, which should occur close to full brightness. Then, press and hold the touch plate until the lights dim to a point below where there is no flickering. Remove your hand again and then do a quick press on the touch plate to switch off the light(s). This action will set the maximum lamp brightness at the last used brightness level. The dimmer will use this level from now on as the maximum brightness setting, even if mains power is lost. Recalibration of the maximum brightness can be performed by repeating the procedure, starting by switching off power to the lights circuit. The maximum brightness can then be set Australia’s electronics magazine at a higher or lower level than the previous setting. Note that the rate at which the lamp brightness increases during this procedure is purposefully slow, so you can set brightness with reasonable precision. Note also that once you start the calibration procedure by touching the dimming plate, you have up to five seconds after you remove your hand to re-apply it to the plate to start reducing the brightness. There is another five second timeout period after you removing your hand having reduced the brightness before you touch it again, to switch off the lamp. If you do not touch the plate before these five second periods elapse, calibration will be aborted and the previous maximum brightness value will be used. You will have to start again. Keep in mind that the calibration should be done with the lamps you are going to use with the dimmer. If you use different LED lamps or an incandescent lamp, the maximum nonflickering brightness setting may be different. In operation Note that the dimmer plate usually runs just warm to the touch, due to the dissipation within Mosfets Q1 and Q2 of around 1W total. The remote control must be directed toward the receiver on the main dimmer plate to obtain reliable operation. We found that our prototype worked well up to 7m away from the wall plate, as long as the remote control was correctly aimed. SC March 2019  83