Fullscreen HTML5Med Res (??MB)HTML4

BUILD IT NOW IN TIME FOR YOUR CHRISTMAS EXTRAVAGANZA! DIGITAL LIGHTING CONTROLLER Part 1 – by Nicholas Vinen and Jim Rowe Want one up on your neighbours? Instead of a static Christmas Lights display (so passé!) now you can have the ultimate in Christmas extravaganzas. This amazing controller will bring your Christmas lights to life, making them flash, dim up and down, you name it, all in time with your favourite Christmas music. It’s easy to build, easy to connect and, best of all, easy to program! O K, we have to admit it. We first had this idea after watching Chevy Chase’s “Christmas Vacation”. Then it was given further impetus by a YouTube clip we saw a couple of years ago. It’s taken a while to put the idea into practice! You’ve probably seen the clip we’re talking about. Just one version of it has had nearly seven million hits! But if you haven’t and/or if you’d like to see the inspiration – and get some idea of what this will do for you, check out www.youtube.com/ watch?v=rmgf60CI_ks (or simply en36  Silicon Chip ter “Christmas Lights” on YouTube). Actually, we lie: we’re pretty sure that controller only had about 12-16 channels. Ours has up to 32, so you’ll be able to put that to shame. Just imagine the neighbours – they’ll be as amazed as everyone else who stops to admire your handywork this festive season. There are certainly some amazing displays this time of year. But for the most part, they’re static. Most don’t DO anything except look pretty. With this controller, yours can look pretty AND look spectacular at the same time. We know that quite a number of readers have used SILICON CHIP’s DSP Musicolour Lightshow (June-September 2008) to control their Christmas Lights, flashing them in time with music. That’s fine, of course, if all you want is flashing lights. Like the Musicolour, this unit has multiple high-current Triac outputs capable of phase-based brightness control. But that’s where the similarities end. With this new controller (or more properly called a sequencer) you can program in specific lighting patterns and movements, similar to the siliconchip.com.au MAINS IN CAT5 CABLE INFRARED RECEIVER  MAINS IN (OPTIONAL) 1-3 SLAVE UNITS SLAVE UNIT (8 TRIAC OUTPUTS) dsPIC33FJ64 GP802 MICROCONTROLLER (IC1) SD/MMC CARD RJ-45 JACK RJ-45 JACK MAINS-POWERED LIGHTS AUDIO FILTER (IC2) ZERO-CROSSING DETECTOR RJ-45 JACK MAINS-POWERED LIGHTS Fig.1: the block diagram showing how both master and slave units operate. The master unit plays the music and sends commands to the slaves which in turn control the lights. An infrared remote can be used to control the whole lot. LINE LEVEL STEREO AUDIO OUTPUT AC-TO-DC REGULATED POWER SUPPLY 9V AC PLUG PACK YouTube clip above. We decided that for this application, rather than attempt to synchronise the light show with music being played from another source, it would be best to have the Controller itself play the music AND sequence the lights. This makes for a self-contained project which will always keep the light sequence strictly in time with the music. The hardware The hardware is split into two sections. One is a small plastic box containing the master unit while a larger instrument case houses the slave unit. Between one and four slave units, each of which controls up to eight channels, can be connected to the master. The master unit, which is controlled via a hand-held remote, plays the music and a sequencer file (which you set up) from an MMC (MultiMedia Card), SD (Secure Digital) card or SDHC (high capacity) card. It sends serial commands to the slaves via a Cat5/6 cable with up to 30m between the units. Splitting the project into two parts has two advantages. Firstly, only the slave units contain mains wiring, making it easier to build them safely. Secondly, you can build the number of outputs you need. One slave with eight channels will drive a small light show while four slaves, totalling a whopping 32 channels, will create a lighting RJ-45 JACK spectacular worthy of a Broadway hit! Each slave has eight mains output sockets but you can use as many or as few of these as required. While each of the eight slave channels can drive lights up to 1200W at 230V AC (5A), the total amount of power allowed per slave unit is 2300W, limited by the 10A input socket and fuse. The power figures are halved for 115V AC mains. Since we have designed this project for use anywhere in the known universe, mains supply frequencies of 50Hz and 60Hz are supported. Because the slave power limit is 2300W, if you are using all eight channels with identical lights, the The master controller fits into the smaller box on top, while each 8-channel slave unit requires the larger case below. Up to four slaves can be connected. siliconchip.com.au October 2010  37 Features Audio THD+N..............................0.06% Audio Signal-to-Noise Ratio.......65dB Audio sample rates (kHz)...........11.025, 12.0, 22.05, 24.0, 32.0, 44.1, 48.0 Audio file formats.......................WAV format, 16 bit PCM, mono or stereo Music capacity............................At least 4GB (ie, more than six hours at CD quality) Playback order............................By directory order, alphabetically or random (shuffle) Number of light “channels”.......32 (max. 4 slaves = 32 channels) Light power per channel.............25-1200W (230V AC) or 12-600W (115V AC) Total light power (four slaves)...9200W (230V AC) or 4600W (115V AC) Extra features..............................Remote control, Filament preheat, Volume control Infrared formats supported.........Philips RC5 12-bit, NEC 16-bit maximum power per channel would be 287W (1.25A). We don’t believe that will normally be a problem because (a) most Christmas Tree “bud” light strings are only 1050W or so and (b) even PAR38 coloured floodlights are usually only 100W. The 1200W per channel figure is only possible if some channels are left unused or have lighter loads. If you wanted to run four slave units giving up to 32 channels, you could do so by spreading them over separate same-phase mains circuits, each of which is normally limited to 15A. That does NOT mean running four slaves from the one powerboard or double adaptors! (Don’t laugh – we’ve seen much worse . . .) While a personal computer is used to initially set up the music files and sequences, no PC is required for playing the music or controlling the light sequence. This results in a simplified set-up with increased safety and less power consumption. The music output Finally, the master unit also has a line-level audio output to drive virtually any amplifier, perhaps with outdoor speakers so everyone can enjoy the music and lightshow. Perhaps your neighbours may not be too happy for you to set up loudspeakers playing Christmas music continuously along with your light show (bah, humbug!). As suggested by a reader last month, one clever solution is to wire up a small FM transmitter (build from a kit or purchased as a retail device) so that people can tune in and listen in their cars or even their mobile phones while watching the show. A sign out the front could say “to listen in, tune your car radio to 88.X MHz” (or something similar). Just make sure you don’t pick a frequency occupied by an FM radio station in your area! Apart from Christmas Lights? This project isn’t just limited to a Christmas Light application. It can be used any time that you want lights to be controlled synchronously with audio. For example it could be used in a museum exhibit, where pressing a button activates narration explaining the exhibit while the appropriate sections are lit up in turn. Or it could be used as part of an art project, where music and/or narration/ music/sound effects are accompanied by different sections being illuminated Here’s the main sequencer unit with DC power input, infrared receiver, data output socket, SD/SDHC/MMC card reader (under PC board) and at right, the 3.5mm audio output socket. Full construction details will appear next month. 38  Silicon Chip siliconchip.com.au or devices powered up and down. Another suggestion is to provide mood lighting or even to switch lights on and off over the course of a day when you are away from home, so that it looks like somebody is still there. Not only will you achieve a much more realistic light pattern than with a switchboard (the usual method), you can also have music playing to make you home look really occupied! We’ve designed the switching so that theoretically other mains devices (eg, small motors, etc) can also be controlled but of course, if this is done, “dimming” via phase control must not be attempted! It really is intended to be used with resistive loads, à la lights. How it works Refer to Fig.1, the block diagram. At the heart of the project is the dsPIC33FJ64GP802 microcontroller from Microchip. It has 64KB of FLASH program memory, 16KB of RAM (random access memory) and will processs up to 40 MIPS (millions of instructions per second). This IC is responsible for controlling all the functions of the sequencer, including music playback and Triac triggering/phase control (see panel). During a light show, the dsPIC chip reads one WAV audio file at a time from the attached MMC/SD/SDHC card and plays it back using its internal digitalto-analog converter (DAC). The output of the DAC goes through a filter which removes some of the digital noise. The resulting signal level is around 1V RMS, which is compatible with most amplifier “aux” (line level) inputs. As well as a hifi/stereo power amplifier, it could be connected to an FM transmitter, headphone amplifier, mixer, etc. Power for the master module comes from a 9V AC plugpack. There are two reasons why we are using an AC plug- pack rather than DC. Firstly, we need to know when the mains zero-crossing events occur to enable phase control of the lights, for brightness adjustment. Secondly, this makes it easy to generate balanced supply rails for the audio filter op amps. A higher voltage plugpack cannot be used as that risks exceeding the op amp supply ratings. The power consumed from the plugpack depends upon how many slave modules are connected and the specifics of the light sequence but as a rough guide, with one slave module and eight active light channels it can be expected to be below 250mA/2.5W. The zero-crossing detection is done by IC1’s internal comparator. This compares a reduced amplitude signal from the plugpack AC output to a halfsupply rail, resetting a timer each time they cross. By measuring how long this timer Inside one of the slave units. It’s basically a mains switching box, under the control of the signals sent by wire from the master sequencer unit. Each of the eight channels has its own Triac with interference suppression and an IEC mains output socket. Front panel LEDs can mimic the mains output. siliconchip.com.au October 2010  39 runs, IC1 can determine the mains frequency (50Hz or 60Hz). It needs to know this in order to convert the desired phase angle for each light to a time delay for Triac triggering. D3 9V AC IN A User interface The behaviour of the master module is controlled in two ways. Firstly, its default setting are specified in the optional configuration file which is stored on the MMC/SD/SDHC card. This allows you to determine whether the music files are played 40  Silicon Chip OUT IN REG2 LM3940T +6V GND 2200 F 16V CON1 IN +3.3V OUT GND 100 F 100 F D1 Synchronised sequence playback When the microcontroller opens a WAV file for output, it also looks for a file with the same name but a different extension (.lsq). This file contains the light sequencing information which you have prepared to demonstrate your lighting brilliance (OK, pun intended!). It is processed at the same rate as the WAV file is played so that they remain synchronised. The information it contains indicates when to switch lights on and off, when to change their brightness and what the new brightness settings are – either a fixed percentage of full brightness or indeed fading up/down. At the appropriate times during each mains half-cycle, IC1 sends serial data out over the RJ45 jack connection. This is carried to each slave module in turn, where the serial data is latched and used to determine which Triacs to trigger. As a result, IC1 controls the lights in each slave module as determined by the sequence file. This sequence file is generated with the Windows software we have developed, which will be available from the SILICON CHIP website next month (at the same time as the article containing the construction details). We will also provide source code for this software for any users who are interested in porting it to other operating systems like Mac OS X or Linux. The light sequence can be generated manually, by using the GUI to indicate at which point in the music to change the output light states. Or, to save time, the control for some light channels can be automatically derived from the music itself over a given time period, with adjustable parameters to determine how it behaves. The result can be used as-is or can be further edited to your satisfaction. REG1 7806 K A V+ K +6V 470 F 25V 470 F 25V D2 K +3.3V A 10k 3k V– 27k 4.7 F 28 AVdd 1nF 4 Vdd MCLR RB2/AN4 RB0/AN2 RB3/AN5 NP 3.0k 3k 390 D4 K A RB4 RB5 10k RB7 IRD1 100nF 3  5 1 3 RA0/AN0 Vdd 15 SD CARD SOCKET 17 18 +3.3V CLK 21 DATA OUT 22 100nF RB5 SC 100 3 x 100 14 16 2 23 DAC1R+ RB6 DAC1R– RB8 RB9 24 10k 10k 10k 10k Vcap 20 RB10 CLK1 RB11 27 Vss 8 9 X1 24.576MHz CLK0 10 Vss 19 33pF CON4 2010 11 26 DAC1L– AVss WP 7 IC1 dsPIC33FJ64GP802 DAC1L+ 25 12 CS DATA IN 6 RA1/AN1 47k CARD DET CD 100nF RB1/AN3 2 10k 100nF 1 13 33pF DIGITAL LIGHTING CONTROLLER – MASTER UNIT Fig.2: the master unit circuit. At its heart is IC1, a dsPIC running at around 40MHz. IC2 provides gain and filtering for the audio output. Communication with slave units is via CON3 while the music and sequence data are read from the card plugged into CON4. back in order or randomly, which file to start with, whether playback starts immediately when power is applied or must be triggered manually and several other options which control the slave unit behaviour (more on those later). Further control of the master module is made via the infrared remote control. Available functions include stopping, starting and pausing playback, changing audio tracks, adjusting the volume, playing a specific track, changing the playback order and so on. The default remote control codes are set up to suit common universal remotes but they can also be changed using the configuration file. Cabling We chose Cat5 cable to connect the slave modules because it is readily available in a variety of lengths, can be made to length, has an appropriate number of conductors (eight) and is weatherproof. This should enable constructors to easily connect multiple slave modules in different locations, to control a large array of lights. Because the serial data is buffered by each slave module, this does not limit the total cable length and so 30m cable siliconchip.com.au +3.3V TO SLAVE MODULE(S) 1 2 3 4 5 6 7 8 V+ +6V 10k CON3 RJ-45 10k 220 A  LED9 K IC2: TL072 3 2 8 10 F 1 IC2a 13k 150pF 10k 15nF 10k 15nF AUDIO OUTPUT CON2 100nF 5 6 100 10 F 7 IC2b 3.5mm STEREO JACK Slave control 100 4 13k 10 F 13k 150pF 13k 10 F V– 10 F LED D1–D3: 1N4004 A K K A runs between each unit are possible. In fact longer cable runs may work fine but 30m is the longest pre-formed cable that is commonly available. Our test set-up is as follows. We ran a 2m Cat5 patch cable from the master unit to a wall socket which was wired to another wall socket approximately 20m away. Including the vertical runs and other diversions the actual cable run is at least 25m. We then connected a 5m Cat5 patch cable from the other wall socket to the slave unit. There were no apparent serial data errors over this distance and the voltage drop on the 6V line was acceptable siliconchip.com.au 7805, LM3940T IRD1 1 2 GND IN 3 to perform all these tasks is complex. We will not go into great detail in this article, however the source code will be available for download along with the HEX file. During playback, both the WAV and sequence files are read off the MMC/ SD/SDHC card synchronously, ie, the software waits for each data packet to arrive. Therefore, the other functions which must be handled simultaneously – DAC output, infrared sensing, zero crossing detection, phase control, etc – must be interrupt driven. Direct Memory Access (DMA) is used for the DAC output and SD card access to improve efficiency. A number of software modules are required to enable the various functions. These include the MMC/SD/SDHC card driver, FAT file system support, WAV file reader, DAC driver, sample rate and clock speed setting functions, infrared decoding, mains phase synchronisation and serial output, audio state playback logic and slave chain length sensing (which uses the internal ADC). GND OUT (a little over 100mV with all eight lights on). Four such cable runs would produce a total of around 400-500mV loss on the 6V line. In normal circumstances, assuming typical device characteristics, this will leave a high enough voltage at the last slave to reliably trigger its Triacs. However to be safe it is best to keep the total cable run under 50m if possible, especially if wall sockets are involved. Firmware While the hardware of both the master and slave modules is fairly straightforward, the software required for IC1 The reason that the software calculates the number of attached slaves is that if there are only one or two, it can use the lowest possible serial frequency (72kHz) and only needs to transmit 16 bits (one word) per trigger point. With three or four slaves, the serial frequency is increased to 96kHz so that 32 bits (two words) can be transmitted at each trigger point and will be finished before the next trigger point is reached. These trigger points are spaced approximately half a millisecond apart and there are up to nineteen trigger points per mains half cycle. In order to allow for smooth brightness control (256 levels), the trigger point used for a given light is “dithered”, ie, it is rapidly toggled back and forth to give intermediate brightness levels. Because of the filament heat persistence and the persistence of our vision, this rapid brightness variation is not visible. This scheme reduces the required serial rate and makes the microcontroller’s job easier as it can more often send the trigger even for multiple lights together in a single command. In choosing when to trigger a given TRIAC, the microcontroller also takes account of the fact that the amount October 2010  41 10k CON1 CHAIN LENGTH SENSE IN FROM CONTROLLER 1 2 3 4 5 6 7 8 +3.3V SER DATA +6V GND RJ-45 13 SER DATA MASTER CLEAR 14 12 100 10 11 IC2e IC2f IC4: 74HC04 2 1 SCLK 9 3 100 IC2d IC2a LATCH 100nF 8 4 5 IC2c 100 6 7 IC2b +6V 100 F 16V 100nF 100 100 F 16V IC5 ULN2803 10 COM 16 10 11 14 12 13 10k 10k 10k 10k Vdd MR Q0 Q1 SRCK Q2 Q3 DS 15 1 2 3 IC3 Q4 4 74HC595 5 Q5 LCK Q6 Q7 Q7' OE 6 7 9 8 8B 8C 11 7 7B 7C 12 6 6B 6C 13 5 5B 5C 14 4 4B 4C 15 3 3B 3C 16 2 2B 2C 17 1 1B 1C 18 Vss 8 SC DIGITAL LIGHTING CONTROLLER SLAVE UNIT LED1  A 47 K K    A 47 47 A  47 47 K K A A K K   A 47 47 A K  A 47 E 9 ERRATA: when operating the unit with four slaves, it may be necessary to leave the 10kW “chain length sense” resistor off one of the four slave boards for correct operation. You can check this by plugging in three slaves, then four; if it works with three but not four, remove that resistor from the fourth slave. 2010 K BTA41–600B LEDS K A A1 A2 G Fig.3: the slave unit uses IC1, a serial-to-parallel latch, to decode the control data. Its outputs drive IC3, an eight Darlington array, which switches current through the optocoupler LEDs (OPTO1-8). These control TRIAC1-8 and ultimately the lights. The optocouplers and TRIACs are both equipped with snubber networks to prevent false triggering and an LC filter to reduce radiated EMI. IC4 buffers the serial stream to the next slave unit. of power delivered does not vary linearly with the trigger phase angle. It has a lookup table which allows it to calculate the percentage of full power that a light will receive for each given trigger period . This is compared to the desired brightness level and the dither error from the last trigger event in order to 42  Silicon Chip calculate the appropriate trigger point. Because the master module senses mains zero crossings via its AC plugpack supply, by default it assumes that the slave modules are all on the same mains power phase as it is. This will be true in the vast majority of cases as most residences use a single phase for all power outlets. While it is possible to run the controller across multiple phases (indeed, the software can handle this) in the interests of safety and simplicity we do not recommend operation on more than one phase. Another configuration option which affects slave behaviour is the filament preheat control. Filament preheating siliconchip.com.au CON2 1 2 3 4 5 6 7 8 SCLK SER DATA +6V LATCH GND OUT TO OTHER MODULES +3.3V CHAIN LENGTH SENSE MASTER CLEAR RJ-45 +6V OPTO1 MOC3021 1 360 6 47nF 275VAC X2 G  4 2 360 6 TRIAC1 BTA41 –600B A1 39 10nF 275VAC X2 100 H 100nF 275VAC X2 OUTPUT 1 N A 470 47nF 275VAC X2 G  4 2 A2 E OPTO2 MOC3021 1 470 A2 TRIAC2 BTA41 –600B A1 39 10nF 275VAC X2 100 H 100nF 275VAC X2 OUTPUT 2 N A E (TRIAC SWITCHING CIRCUITS 3–7 NOT SHOWN) OPTO8 MOC3021 1 360 6  2 4 470 A2 47nF 275VAC X2 G TRIAC8 BTA41 –600B A1 39 10nF 275VAC X2 100 H 100nF 275VAC X2 OUTPUT 8 N A E NOTE: ALL WIRING AND PARTS IN THIS SHADED AREA OPERATE AT MAINS POTENTIAL. CONTACT COULD BE FATAL! FUSED MALE IEC CONNECTOR WITH SWITCH F1* * FUSE F1 RATING: 10A FOR 230V, 15A FOR 120V means that when lights are off, their power will not drop to zero. Instead, the filaments are run just below red heat which means that high repetitive surge currents are largely eliminated when they are being turned on and off frequently. Two options are provided. One specifies which outputs have lights siliconchip.com.au E A N that require filament preheating and the other determines what percentage of full power is delivered during the off-state. Circuit description Refer to Fig.2 for the master unit circuit diagram. Power from the 9V AC plugpack is delivered via CON1 then rectified separately for two supplies. Diodes D1 & D2 form a full-wave voltage doubler, charging the two 470F filter capacitors to generate an unregulated split supply of approximately ±13V. This is used to power the op amps. At the same time, diode D3 halfwave rectifies the AC input, charging a 2200F filter capacitor for the digital supply. This is regulated to 6V by REG1 and powers the optocouplers in the slave modules. It is further regulated (by REG2) down to 3.3V for the remaining digital components, including microcontroller IC1 and the digital logic in the slave modules. The 6V rail voltage is dropped by D4 and then further by the 390 resistor to provide a 4.5-5.5V supply for the infrared receiver. This assumes that its current consumption is in the range of 0.5mA-1.5mA, which is that of the receivers specified in the parts list. The 390Ω resistor and the 100nF capacitor filter its supply so that any digital switching spikes do not upset its internal amplifier. Pins 4 and 5 are connected to IC1’s internal voltage comparator and this is used for mains zero crossing detection. The AC input voltage is divided (with a 10:1 ratio) by the 27kΩ and 3kΩ series-connected resistors, resulting in a 0.9-1.1V AC sine wave at their junction. Two 3kΩ resistors hold pin 4 of IC1 at approximately 1.65V (half the 3.3V supply). The reduced amplitude sine wave is AC-coupled to pin 5 of IC1 and also biased to the 1.65V level via a 10kΩ resistor. For half of each mains wave, the voltage at pin 5 is higher than the voltage at pin 4 and the rest of the time it is lower. IC1’s comparator generates a software interrupt every time this changes, allowing it to synchronise a timer to the zero crossing event. In reality, the voltage at pin 4 does not stay at exactly half supply as current flows back through the 10kΩ biasing resistor but this does not affect the zero crossing detection. Since comparators tend to have an offset voltage between their inputs, the zero crossing detection is only accurate to within about ±2%. This is taken care of by the software with the insertion of a “dead zone” around the zero crossing point. The 1nF capacitor between pins 4 and 5 suppresses mains October 2010  43 Phase controlled Triacs, serial data SERIAL CLOCK PULSES (TRAILING EDGES MARK POTENTIAL TRIGGER POINTS) In essence, this Digital Lighting Controller can be thought of as a multi-channel light dimmer, all under the control of the dsPIC micro which in turn is responding to commands written for a particular piece of music stored on the SD card. But how do the light dimmers work? Just the same as the light dimmers in your home, they are based on a Triac, a four-layer semiconductor device that can switch high voltage AC. When triggered, a Triac stays on until the voltage across it drops to zero or reverses. We vary the power fed to the lamps by triggering the Triac earlier or later in each mains half-cycle; the more power the lamp gets, the brighter it will be. This is known as “phase control” as we are varying the portion of the mains waveform which the lamps receive. The accompanying diagram illustrates Triac triggering on 230VAC mains waveforms, A, B and C. A corresponds to high power since the Triac is on for most of the time. B corresponds to slightly less power, as the Triac is triggered later in each AC half cycle. And C corresponds to the lowest power normally used in the Controller, equivalent to the “filament preheating” referred to elsewhere. Note that while only three Triacs are depicted here, the Controller can drive up to 32 channels (in four slave units). The serial data stream at the top of the diagram is fed to the serial-to-parallel latch (IC5) and the trailing edge of each data pulse defines the start of a gate signal fed to each Triac. Each Triac’s gate signal (trigger) is on for the time between successive serial data pulses or around 0.5ms. Each Triac stays on for the rest of the half-cycle due to its latching action. and power supply noise, preventing false comparator triggering. Infrared receiver IRD1 detects infrared light pulses at the appropriate frequency (around 36kHz). Its logic level output goes straight to IC1’s RA1 input (pin 3). This pin is configured to generate an interrupt on a level change and this triggers a decoding sequence whenever infrared pulses are received. The MMC/SD/SDHC card socket CON4 is wired directly to IC1, which uses an internal SPI peripheral to communicate with the card. The MMC/ SD/SDHC card is powered from the regulated 3.3V rail. Pull-up resistors 44  Silicon Chip 0 5 10 LAMP POWER A 15 20 TIME IN MILLISECONDS EARLY TRIGGERING: HIGH LAMP POWER LAMP POWER TRIAC TRIGGERING TRIAC TRIGGERING (TRIAC GATE PULSES) LAMP POWER B LATER TRIGGERING: LOWER LAMP POWER LAMP POWER TRIAC TRIGGERING TRIAC TRIGGERING (TRIAC GATE PULSES) LAMP POWER LATE TRIGGERING: LOW LAMP POWER LAMP POWER C TRIAC TRIGGERING TRIAC TRIGGERING (TRIAC GATE PULSES) are provided for the card’s CS and DATA OUT pins in order to ensure it is not activated at the times when IC1 is not operating (eg, when it is powering up or reset). Input RB5 (pin 12) has a weak internal pull-up enabled. The card socket connects its card detection (CD) pins together if a card is inserted, pulling IC1’s pin 12 low and triggering its communication initialisation routine. Audio output Audio output is generated from IC1’s internal 16-bit DAC and then passes to IC2, a dual op amp. The left/right DAC outputs are differential, meaning that when DAC1L+ swings up, DAC1Lswings low. For best audio quality, these signals should be subtracted to form the final audio output. IC2a and IC2b are configured as differential amplifiers with a gain of 1.3 (13kΩ/10kΩ), resulting in an output level of around 1V RMS. The two 10F capacitors in series with the 13kΩ resistors charge to the DAC’s average output voltage and form a virtual ground for the differential amplifier input dividers. They result in a high-pass filter with a -3dB point at around 1Hz. siliconchip.com.au Parts List – Digital Lighting Sequencer/Controller Master module 1 PC board, coded 16110101, 148 x 80mm 1 front panel label, 145 x 20mm 1 2.5mm PC-mount DC socket (CON1) 1 3.5mm PC-mount stereo switched socket (Jaycar PS0133, Altronics P0092) (CON2) 1 low profile RJ-45 socket (Altronics P1448) (CON3) 1 surface mount MMC/SD/SDHC card socket (Altronics P5720) (CON4) 1 24.576MHz crystal 1 ABS plastic instrument case, 86 x 155 x 30mm (Altronics H0377) 4 nylon washers 4 No.4 x 9mm self-tapping screws 1 9V AC plugpack 500mA+ (Altronics M9231, Jaycar MP3027) 1 SD, MMC or SDHC card, at least 1GB recommended 15cm tinned copper wire 1 28-pin DIP socket 2 M3 x 6mm machine screws 2 M3 shakeproof washers 2 M3 nuts 1 mini TO-220 heatsink (Jaycar HH8502, Altronics H0630) Semiconductors 1 dsPIC33FJ64GP802 microcontroller (IC1) programmed with 1911010A.hex 1 TL072 dual op amp (IC2) 1 infrared receiver (IRD1) (Jaycar ZD1952, Altronics Z1611/Z1611A) 1 7806T regulator (REG1) 1 LM3940IT-3.3 regulator (REG2) 1 green 5mm LED (LED9) 4 1N4004 diodes (D1-D4) Capacitors 1 2200F 16V 2 470F 16V 2 100F 16V 4 10F 16V 1 1 0F 16V tantalum 1 4.7F non-polar (NP) 5 100nF MKT 2 15nF MKT 1 1nF MKT 2 150pF ceramic 2 33pF ceramic WARNING! This is a mains-operated device. Construction should not be attempted unless you have knowledge of and experience in building mains-powered projects. The slave unit has areas of the PC board where components and tracks are at mains potential. Contact with live wiring could prove fatal. siliconchip.com.au Resistors 1 47kΩ 1 27kΩ 3 3kΩ 1 390Ω 4 13kΩ 1 220Ω 11 10kΩ 6 100Ω Slave module (parts for one module [eight channels] only) 1 PC board, code 16110102, 216 x 157.5mm 1 plastic instrument case, 260 x 190 x 80mm (Jaycar HB-5910, Altronics H0482) 1 aluminium rear panel for above case, 2mm thick 1 front panel label, 240 x 71mm 1 rear panel label, 240 x 71mm 2 low profile RJ-45 sockets (Altronics P1448) 8 100H 5A mains-rated inductors (Jaycar LF1270, Altronics L6622) 4 heavy-duty PC-mount TO-3P heat sinks (Jaycar HH8526, Altronics H0667) 5 2-way mini terminal blocks (5.08mm pin spacing) 1 1.5mm panel snap-in male IEC mains connector with fuse and switch (Altronics P8341) 8 chassis-mount female IEC mains connectors (Altronics P8326) 15 blue fully-insulated 6.4mm female spade crimp lugs 17 red fully-insulated 6.4mm female spade crimp lugs 1 chassis-mount male spade lug 1 5.3mm eyelet crimp lug 20 small nylon cable ties 6 No.4 x 9mm self-tapping screws 22 M3 x 10mm machine screws 24 M3 shake-proof washers 24 M3 nuts 2 10A M205 fuses (1 spare) 1.2m mains-rated green/yellow (earth) wire 1.1m mains-rated light blue (neutral) wire 0.8m mains-rated brown (active) wire 40cm tinned copper wire 15cm x 2.5-3mm diameter fibreglass sleeving (Jaycar WS5504, Altronics W0852) Cat5, 5e or 6 cable with length to suit installation Semiconductors 1 74HC595 serial-to-parallel latch IC (IC3) 1 74HC04 hex inverter IC (IC4) 1 ULN2803 octal Darlington array (IC5) 8 red 5mm LEDs (LED1-8) 8 MOC3021 Triac optocouplers (OPTO1-8) 8 BTA41-600B insulated tab 40A Triacs (Triac1-8) Capacitors 2 100F 16V 8 100nF MKT X2 250V AC 2 100nF MKT 8 47nF MKT X2 250V AC 8 10nF MKT X2 250V AC Resistors 5 10kΩ 8 470Ω 8 47Ω 8 39Ω 8 360Ω 4 100Ω October 2010  45 The bootloader The master module firmware includes a “bootloader”. This allows the software on the master module to be updated without requiring a programming tool. When the device powers up it looks for a HEX file on the memory card. If it is present, the contents are read and verified, then written into the FLASH program memory. The main program runs after the programming is complete, or immediately if there is no HEX file. The main program can re-program the bootloader if necessary, allowing the whole chip to be updated. The FLASH memory is divided in two. The bootloader resides at the end of memory, (addresses 0x9000 – 0xABFF, 10.5kB). The main program is at the start (addresses 0x0000-0x8FFF, 54kB). The bootloader program incorporates the MMC/SD/SDHC card reader code along with the FAT file system and FLASH memory programming routines. Because the interrupt vector table is stored in FLASH memory at 0x0000-0x01FF and therefore is part of the main program, the bootloader does not use any interrupts. Because the reset vector (which must point to the bootloader) is within the interrupt vector table, when the first page of memory is programmed, the reset vector address is overridden. If the reset vector were corrupted during the programming process, eg due to a power failure, the bootloader would no longer work. Before re-programming it, the bootloader program checks that AC power is present via the zero crossing detection circuitry. The 2200F capacitor provides enough power to finish programming even if AC power is lost after that point. A similar check is made in the main program before re-programming the bootloader. The 150pF capacitors in parallel with the 13kΩ feedback resistors roll off the op amp gain to form a low-pass filter with a -3dB point around 80kHz. This active filter removes much of the high frequency switching noise from the delta-sigma DAC architecture, which is mostly above 2MHz (for CD quality audio). The output of each differential amplifier is AC-coupled to make it ground-referenced, then further filtered with a passive low-pass RC filter consisting of the 100Ω resistors and 15nF capacitors. This is more effective than the active filter at frequencies above IC2’s bandwidth (2.3MHz at this gain setting) which can be coupled via the 150pF capacitors. The 100Ω resistors also isolate IC2’s outputs from any cable capacitance and provide current limiting should the outputs be shorted to ground or to each other. CON2 is the audio output connector and accepts 3.5mm stereo jack plugs. Crystal X1 provides a reference frequency to IC1 for the DAC timing. This allows it to operate the DAC at a frequency very close to the sample rate of the file being played back. IC1 operates at 39.552MHz when the audio sampling rate is 44.1kHz, 22.050kHz (half rate) or 11.025kHz (quarter rate). This is divided by 14, 28 or 56 to provide the DAC oversampling clock, which is 64 times the sample rate. The sample rate error is less than 0.1%. Alternatively, IC1 operates at 39.936MHz for sample rates of 48kHz, 24kHz (half rate) or 12kHz (quarter rate). This is divided by 52, 26 or 13 (respectively), resulting in exactly 64 times the sample rate. For 32kHz sample rate, the clock is 38.912MHz and the divider is 19, also resulting 46  Silicon Chip in an exact DAC clock. While IC1 runs from the 3.3V supply, its core actually runs at 2.5V. This is generated by an internal regulator. Its output is filtered by the 10F tantalum capacitor connected between pins 19 and 20. The master module communicates with the slave(s) via 8-pin RJ-45 connector CON3. This provides the low voltage slave power supply, serial communications and slave chain length sensing. 3.3V is provided for the slave digital logic (pin 3) and 6V for driving the optocouplers (pin 6) plus a common ground (pin 8). The same connector is used for the serial communication with data (pin 5) and clock lines (pin 4), chip select/latch (pin 7) and master clear (pin 2). Pin 1 is for chain length sensing and is used by the master module to determine how many slaves are connected. Each slave module has a resistor between this pin and the 3.3V supply and these form a voltage divider in combination with the 10kΩ resistor on the master board. Each serial output has a 100Ω resistor between the microcontroller output and the connector pin. This combines with the cable capacitance to form an RC filter which helps to limit reflections and ringing in the cable as well as reduces electro-magnetic interference (EMI) from the cables by limiting the signal rise and fall times. Normally, Cat5 cable is used for high speed network signalling and the twisted pairs in the cable are driven differentially. This allows for high speed communication with minimal crosstalk and interference. However, we are not using differential signalling so we must limit the serial speed in order to maintain sufficient signal integrity. This is not a problem as a serial clock of 100kHz is sufficient for this application. LED1 provides the only direct user feedback from the master module and is driven from pin 2 of IC1. It can be turned on or off, set to an intermediate brightness or flashed at various rates to convey different information to the user. Slave module circuit The slave module receives serial data from the master module to control when each of the eight Triacs are triggered during each mains half-cycle. A 74HC595 serial-toparallel latch IC (IC3) decodes this serial data. Each of the incoming lines is terminated with a 10kΩ resistor to help to drain the cable capacitance when a line is driven low. The latch drives a ULN2803 octal Darlington transistor array (IC53) which acts as a current buffer to provide sufficient drive strength for the optocoupler LEDs. These optocouplers have two purposes. Firstly, they isolate the low voltage signal side of the circuit from the mains side so that lethal voltages can not be conducted back to the master module over the Cat5 cable (or shock somebody touching the connector). Secondly, they make triggering the Triacs easy as all that is required is for sufficient current to pass through their internal infrared LED. The minimum guaranteed trigger current is 15mA and the 74HC595 is not rated to provide this much current directly, hence the Darlington array. When an output from IC1 goes high, the Darlington in IC3 sinks current via the associated LED, 47Ω series resistor and optocoupler from the 6V rail. The worst-case voltage drop across each Darlington at 15mA is 1.0V, for the LED around 2.5V and the optocoupler siliconchip.com.au The rear panel of the slave unit is pretty spartan, containing only the eight IEC mains output sockets. These are used mainly for their size – they’re a lot smaller than standard 3-pin power outlets. You will need to make up (or buy) some IEC-to-3 pin plug adaptors if your power leads aren’t terminated in IEC plugs. 1.5V. With a the 6V supply rail at 5.7V (due to regulator tolerances and cable drops), this means that the voltage across each 47Ω resistor will be 0.7V resulting in very close to 15mA through the chain. It’s very unlikely that any particular unit will have all worst-case parts so in reality there is a fair margin for voltage drops across the Cat5 cables. Since the Triacs are only triggered for around 5% of each mains half-cycle, the 100F bypass capacitors in the slave unit should prevent excessive drops on either rail. Triac control When the LED in an optocoupler is turned on, its small internal Triac will conduct bidirectionally. This allows current to flow from the incoming mains active line, through the 470Ω and 360Ω series resistors and then into the connected 40A Triac gate. This will trigger that Triac which will conduct for the remainder of the mains half cycle. Thus, the earlier in the half cycle that the Triac is triggered, the higher the RMS current through the load. Because the Triacs have a latching action, the trigger current does not need to be provided for very long. Each trigger pulse lasts for around 0.5ms. The 470Ω resistors and 47nF X2 capacitors at each optocoupler act to limit the rate of change of the voltage across its internal Triac, ie they function as a snubber. This prevents spurious triggering of the internal Triac (and hence the associated 40A Triac) due to mains noise or electromagnetic interference. Similarly, the 39Ω resistors and 10nF capacitors connected in series across each BTA41 Triac limit the dV/dt rate across the Triac terminals to prevent unintentional triggering from mains supply noise and such. This is especially important when the Triac is driving an inductive load, such as a halogen transformer, as the switch-off spike when the load is disconnected can easily result in the Triac being triggered at the start of the next cycle when it should not be. The 100H inductors and 100nF X2 capacitors form an LC filter which limits the inrush current to the load when the associated Triac switches on. This is primarily to prevent magnetic radiation from the mains leads connecting each load, which can be quite severe when applying phase control to loads such as incandescent lamps. This is due to the high inrush currents when the filament is cold. While each Triac is rated at 40A, the entire slave module is powered from a 10A input socket with appropriate fuse. In addition, other components in the mains power path (such as the inductors) are rated at 5A, so this is the maximum current per output. There are two reasons why we are using 40A Triacs desiliconchip.com.au spite the much lower continuous rating. The first is that when an incandescent lamp is switched on from cold, its filament resistance is a lot lower than when it is at operating temperature. A 230V AC 150W lamp can be expected to have an overall resistance of around 350Ω at full power. It will therefore draw about 230/350 = 657mA RMS. However when the filament is cold, eg when switched on initially, the resistance can be 10% of this or less. This will result in an instantaneous current in excess of 6A and even higher for larger lamps or several in parallel. Even higher currents can occur when a PAR (parabolic aluminised reflector) light fails. The filament can become disconnected at one end and flail around, possibly shorting against the support wires. In excess of 20A can flow before the stem fuse blows. We don’t want to burn out a Triac under this condition so we have made sure that they will survive such an event. One further point regarding the Triacs: they only latch with a certain minimum current flow. In the case of the BTA41 this is no more than 80mA. This is the reason why we have specified a minimum load of 25W per output. Otherwise, early or late in the mains cycle when the instantaneous mains voltage is relatively low, the Triac may fail to latch, resulting in an incorrect brightness level on that output. Daisy-chained slaves The remaining circuitry in the slave module allows for slave daisy-chaining. Up to four slave modules can be connected to a single master module. To ensure that the same length of cable can be run between slave units as can be used between the master and the first slave, we buffer the serial signals using a 74HC04 hex inverter IC (IC4). The SCLK, LATCH and MASTER CLEAR signals are passed through directly from one slave to the next. Each is inverted twice, in order to buffer the signal but preserve the polarity. As with the master module, there are 100Ω series resistors between the buffer and the output RJ-45 jack. The serial data stream itself comes from the Q7’ output of IC1 and via another 100Ω series resistor. This output from this pin is delayed by eight clocks relative to the serial input. As a result, when 16 or 32 data bits are shifted through the slave module chain, each serial latch ends up with a different set of eight bits – the first slave latches the first eight, the second slave the second eight, etc. This allows the master to control each slave individually with a single serial sequence. That’s it for this month. Next month we will show you how to build the master and slave modules and explain how the firmware and PC software works. We will also provide a location to download the PC software. SC October 2010  47