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Plug in any lamp – dim up or down remotely and automatically 24  Silicon Chip 24  Silicon Chip siliconchip.com.au Remote Controlled, Automatic Table Lamp Dimmer by John Clarke Features • Remote control operation • Uses commercial pre-programmed remote control • On and off control with soft start for long lamp life • Fast and slow dim up and dim down control • Automatic dim up and dim down • Programmable minimum and maximum dimming levels • Programmable automatic dimming rate • Dimming level and dimming rate kept even after a blackout • Remote control acknowledge indication • Automatic dimming indication • RFI suppression • Four remote control codes available siliconchip.com.au JJuly 2005  25 uly 2005 83 July 2005  25 D o you want more features from a plug-in lamp than room. It provides such a slow reduction in light over a period of time, that the children probably won’t even notice just boring old on and off? before they fall asleep! This multi-featured Automatic Lamp Dimmer Automatic dimming can be set from a minimum of 10 provides total control via an infrared remote. Use it for mood lighting, home theatre lighting or even as a night light. seconds through to 990 seconds (16 minutes and 30 secWall-mounted lamp dimmers (ie, those that control the onds), in 10 second increments. The maximum time period fixed lamps in homes) are common, used to great effect to should be more than enough for most automatic dimming applications. adjust the brightness levels to suit the occasion. The Automatic Lamp Dimmer is housed in a modified However, it is not very common to find a dimmer for a table lamp or other portable lamp. But these lamps can also 4-way mains power board. This provides a robust and professional-looking case. Three of the four outlets are benefit from being able to be dimmed. For example, you may wish to dim the lights in your not used, to provide sufficient space to house the dimmer lounge room and you can do this with the dimmer that circuitry. A cover blocks off the three unused mains outlets and prevents these from being used. controls the main ceiling lights. Two indicaUntil now, Specifications tor LEDs prothough, you’ve • Fast up and down dimming … 2 seconds from one extreme to the other trude through had only on • Slow up and down dimming … 12 seconds from one extreme to the other the cover. One and off control • Switch on rate … 340ms soft start shows when of any other • Automatic dimming rate… adjustable from 10 seconds to 990 seconds the dimmer is lamps. • Minimum brightness setting for automatic dimming … adjustable over full dimming range receiving an inFor a home • Maximum brightness setting for automatic dimming … adjustable over full dimming range frared remote theatre room, • Maximum dimming steps … 125 control signal, being able to • Phase control range … 14° maximum brightness, 158° minimum brightness while the secdim the ancil• Lamp rating … 40W minimum to 150W maximum ond shows that lary lights is the dimmer is important if the automatically dimming (handy if a long dim time is set). The full visual impact of the large screen is to be realised. In fact, if you only use ancillary lighting that plugs into infrared remote signal is received by the internal circuitry the Automatic Lamp Dimmer, the lighting can be dimmed via a red bezel mounted in the end of the power board. automatically over the period of a few seconds, resulting The infrared remote in a “professional” theatre experience. A commercially available, pre-programmed handheld And as the dimmer functions are remote controlled, all the brightness adjustments can be made from the comfort remote control operates the Automatic Lamp Dimmer. These controllers can operate hundreds of different types of your lounge chair. Bring on the popcorn and choc-tops! As a night-light, the Automatic Lamp Dimmer can be set to of TVs, VCRs and satellite receivers by setting a code to slowly dim from full brightness (or from a dimmed brightness) suit the device concerned. To operate the Automatic Lamp Dimmer, you can select down to a preset level over an extended time period. The slow dimming function is ideal for use in a child’s one of four programming codes. The idea is to use a code Our new Automatic Lamp Dimmer is housed in a 4-way power board, modified to suit the inclusion of the PC board. Three of the outlets are not used and are blanked off by the “front panel”. At right is the commercial infrared remote control we used, a “Big 3” from Jaycar Electronics. Most “universal” remote controls would be suitable for use with the Automatic Lamp Dimmer and can probably replace a couple of your existing remotes into the bargain! 26  Silicon Chip siliconchip.com.au that does not operate any of your other devices that are used in the same room. The remote control can also be used to operate your other remote control devices such as TV, VCR and cable/satellite receivers. More elaborate pre-programmed remote controls will operate DVD players and amplifiers as well. As mentioned, the Automatic Lamp Dimmer can be used to control the light in several ways. Simple on-and-off switching of the lamp uses the mute button on the remote control. Press this and the lamp switches on; press again to switch off. Think of this operation as similar to the sound muting on a TV set – a press of the mute switch turns the sound off and a second press sets the sound back to normal. Soft starting When the lamp is switched on, it may appear that it is instantly switched to full brightness. However, in reality it is soft-started. Soft starting means that power is applied to the lamp gradually. This reduces the very high surge current flow that would otherwise occur due to the lamp’s filament being cold. Allowing the lamp filament to warm up more slowly prevents most of the thermal shock most lamps experience, resulting in a much longer life. The soft start brings the brightness of the lamp up automatically from off to full brightness in 340ms. That’s just a third of a second, so in all probability you won’t even notice the difference between this and normal off/on action. By default, the lamp must be soft-started when using the remaining controls for the Automatic Lamp Dimmer. This is because the brightness is brought up slowly using the dimming buttons on the remote control. There are three types of dimming available for the lamp. (1) Fast dimming, using the channel up (+) and the channel down (-) buttons. Press and hold the channel (+) button and the lamp will be dimmed up from fully off to fully on in about two seconds. You can stop the dimming +340V (a) 0V 10ms 0 30ms 20ms TIME NOTE: THIS CIRCUIT CAN BITE! Never plug this project in to mains power without the case fully assembled. Contact with components could be lethal. at any brightness level by letting go the button. Similarly, the channel (–) button will dim the lamp from fully on to fully off over two seconds. (2) Slow dimming is available with the volume up (+) and volume down (-) buttons. With these buttons, it takes some 12 seconds to fully dim the lights from off to on or on to off, again with the position holding if you let go the button. Slow dimming allows you to select precise brightness levels for the lamp if that’s something you need to do. (3) Automatic dimming is initiated with the operate (or standby) button. This is usually the red button and it has a split circle and vertical stroke icon to indicate a power switch. During dimming, the lamp will dim up or dim down with 125 steps in brightness level from full on to full off over the automatic dimming sequence. Dimming will alternate between dimming up to dimming down with each pressing of the operate button at the end of the dimming sequence. The 125 steps means it is not easy to detect any change in brightness level, so the effect is a smooth up or down dim. At any stage during the automatic dimming sequence, the other dimming or on/off controls can be used to stop the dimming sequence and begin the operation selected by the appropriate button. Two preset dimming levels, high and low, can be set to suit your particular application. A preset high dimming level sets the brightness reached when automatically dimming up and a preset low level sets the brightness reached when automatically dimming down. The preset brightness levels can be set to any value required. For example, the preset low level would be set to a low glow from the lamp filament, suitable for sleeping. Or it might be set higher, for home theatre use. Similarly, the preset high level could be set anywhere you desire. The preset levels are selected by setting the required +340V ZERO VOLTAGE DETECT, BRIGHTNESS COUNTER RESET –340V 127V 82V +340V 10ms 0 30ms 20ms –340V –340V 0 FIG.1 PHASE CONTROL Fig. 1 depicts phase control of an alternating voltage. Fig.1a shows the normal AC waveform (ie, that from the power point). Fig.1b shows just what happens if the power is applied for half of each half cycle. siliconchip.com.au TIME –127V MINIMUM BRIGHTNESS PHASE MAXIMUM BRIGHTNESS PHASE TIME 0 20ms –82V MAXIMUM BRIGHTNESS PHASE (b) 0V 10ms 0V 14 158 180 194 MINIMUM BRIGHTNESS PHASE 338 360 14 DEGREES 20 220 250 0 20 0 20 220 250 BRIGHTNESS COUNTER VALUE Fig.2 shows the relative trigger points and corresponding voltages used in the automatic dimmer. A full explanation of these is in the text. July 2005  27 brightness level with the slow dimming controls - the level set during slow up-dimming will become the high preset level and the level set during slow down – dimming will become the low preset level. The levels are only set during slow dimming, not during fast up and down dimming. If you want to set the preset levels for automatic dimming, you set them using the slow dimming, then press the “operate” button followed by the “0” button on the remote control. The “0’ button tells the Automatic Lamp Dimmer to store the new high and low brightness levels that were selected during the slow dimming. This is a two-stage operation for storing the required preset brightness level. It prevents any dimming made using the slow dimming controls from becoming the new preset brightness level unless it is stored using the “0” button during automatic dimming. For obvious reasons, the low brightness preset should not be set at a higher level than the high preset level nor vice versa. If this happens, automatic dimming will not work. The rate of automatic dimming is programmed during automatic dimming using the number buttons on the hand-held remote. One or two numbers can be entered, ranging from “1” through to “99”, which correspond to 10 seconds per digit. So, for example, entering a “1” will cause the automatic dimming to occur over a 10 second period. Entering “10” will set a 100 second (1 minute 40 seconds) automatic dimming period and so on. Note that the number “0” cannot be entered first because that is used for preset brightness storage. “0” can be entered as the second digit for the automatic dimming rate. Once the automatic dimming rate and the preset brightness level values are stored, they will remain with these settings unless changed again. The settings will remain even if there is a power blackout or if the Automatic Lamp Dimmer is switched off at the mains. The first time power is connected to the Automatic Lamp Dimmer, the lamp will initially be set to off. Acknowledgement Whenever the Automatic Lamp Dimmer receives an infrared remote control signal, the acknowledge LED will flash on and off at a rapid rate. It will do this for any remote control code whether it is the correct one or not. During automatic dimming, the auto dimming LED will flash at a one-second rate. This is very useful when the dimming rate is set to a long period, since the LED then indicates that the sequence has started even though it is not noticeable by the dimming of the lamp. It also indicates that the preset dimming level can be set and/or the dimming rate can be programmed, if required. If a number is pressed, the auto dimming LED will flash rapidly for around 0.5 seconds to show that the number or dimming level has been recorded. The second number can be entered when this rapid flashing of the LED has stopped. Also, it is possible to enter the “0” to record the dimming levels, then two other numbers to record the dimming rate if both values are to be changed. Alternatively, just the dimming rate (eg, 25) can be entered or just the dimming preset level using the “0” can be entered on their own. Phase control The lamp brightness is controlled by a phase control circuit. When a lamp is driven from the full mains supply, the filament is supplied with current from 240V AC. 240V is the “rms”, or root-mean-square, value of the AC waveform. Incidentally, it equates (in a resistive load such as an incandescent load) to exactly the same amount of applied power as would be applied by a DC (direct current) source. Put another way, a light globe will be exactly the same bright15 CRYSTAL TIMEBASE START NEUTRAL RB0 (6) ZERO VOLTAGE NEGATIVE EDGE DETECTOR 16 Fig.3: the block diagram shows how the neutral line is used for setting the various trigger points used in the dimmer. LOCK CLOCK RESET ACKNOWLEDGE λ LED1 RA1 (18) λ RA0 (17) LED2 TIMER 1 X1 20MHz BRIGHTNESS COUNTER 0–250 COMPARATOR BRIGHTNESS LEVEL REGISTER & OPERATION RB1-2-3 (7,8,9) TRIAC GATE TRIGGER 20–250 AUTODIM RB5 (11) RB6 (12) RB7 (13) IR SIGNAL λ DECODING RB4 (10) IR MONITOR TIMER 1 IC2 AMPLIFIER DEMODULATOR 28  Silicon Chip siliconchip.com.au (+5V) LEDS 470 µF 16V K A LED1 470Ω λ K A 1k IC2 LED2 λ K A 100nF OSC1 RA0 OSC2 2 100nF 100 µF 16V RB7 2 1 10 IC2 IR RX SHIELD BOX ZENER DIODE – SC 2005 + RB4 A A1 TRIAC1 BT137F 16 100nF 250VAC (CLASS X2) K D1 1N4004 A A2 X1 20MHz 15 L1 75 µH RB0 11 LK1 12 LK2 13 LK3 MAINS INPUT N N E CODE SELECT LINKS E 1.5M 1W 6 Vss 5 BT137F 4.7nF FR102, 1N4004 A 220nF 250VAC (CLASS X2) 1k 1W MAINS OUTLET 33pF A RB6 λ K G 33pF RB5 3 – D2 FR102 39Ω IC1 PIC16F628A -20P 3 1 ZD1 5.6V 1W 2.2k 4 14 Vdd MCLR 7 RB1 8 RB2 18 9 RA1 RB3 17 A + K AUTOMATIC LAMP DIMMER A2 A1 G WARNING: COMPONENTS & WIRING ARE AT 240V MAINS POTENTIAL WHEN THE CIRCUIT IS OPERATING. CONTACT MAY BE LETHAL! Fig.4: here is the complete circuit. A PIC16F628A handles most of the hard work. Please note the warning above! ness powered by 240V rms or 240V DC. The peak value to which the AC voltage rises is significantly more than the rms value – in fact, it’s exactly 1.4142 times – or about 340V. (It’s about 340V and not exactly 340V because 240V rms is what the electricity supply authority aims for – but it can be ±5% so could actually be anywhere from about 228V to 252V). For a 240V AC supply, this means that the voltage will swing from 0V up to around +340V before dropping to zero again. The voltage then swings negative to –340V before going back up to 0V again. The whole process repeats in a sinusoidal waveform at a frequency of 50Hz. Why 50Hz? Because that is the carefully-controlled but again average frequency at which the power is generated back at the power station. If the voltage is only connected to the lamp at say when the voltage is at 340V, the supply to the lamp and hence its brightness will be greatly reduced as shown in Fig.1b. This is because power is only applied to the lamp for half the time – the first part of the “cycle” is wasted. The supply to the lamp is switched off again when the voltage drops to zero. This happens because we are using a Triac to do the switching and Triacs turn themselves off when the voltage (or more correctly the current) drops to zero – see Fig.1. This method of lamp dimming is called phase control. By altering the point in the cycle where the voltage is applied to the lamp, we can provide dimming from fully off through to fully on. Fully off is where the lamp is never provided with current, while fully lit is when the voltage is applied to the lamp at the beginning of the mains cycle. Dimming levels in-between the full brightness and the fully off range can be set by switching the lamp on at a time other than at siliconchip.com.au the beginning of the mains cycle. Circuitry for the Automatic Lamp Dimmer uses phase control and divides up the each half of the mains waveform into 250 discrete sections – 250 between the 0° to 180° positive half cycle excursion and 250 from the 180° to 360° negative half cycle. Each discrete section corresponds to about 0.72°, as shown in Fig.2. The two extremes over which the circuit will dim the lights are from 14° through to 158°. The 14° setting gives maximum brightness (ie, lamp fully on) and the 158° provides the minimum brightness (lamp fully off) phase setting. Why not 0° and 180°? The reason for limiting the dimming range between 14° and 158° is to ensure that the lamp is not switched in the previous half cycle or into the next half cycle. This could happen with a wider dimming range because the zero voltage crossing detection has a degree of uncertainty due to filtering that produces phase changes. Tolerances in the filter components will alter the phase and hence the zero voltage detection point in the mains waveform. Block diagram Fig.3 shows the general arrangement of the automatic dimmer circuit. Most of the operation, with the exception of the infrared amplifier demodulator (IC2), is performed by a PIC16F628A microcontroller, programmed to perform phase control (IC1). It accepts inputs from the mains and from IC2 and provides an output to drive the gate of a Triac. The mains Neutral input (pin 6) provides the phase information. Each time the voltage goes negative, the microJuly 2005  29 Timer 1 in increments of 800ns either faster or slower over each 10ms period. Should the 100nF 100 µF A brightness counter alter from its 250 count at ZD1 D2 REMMID OTUA each zero crossing, Timer 1 is adjusted to com33pF L1 pensate for the difference. By remaining in lock, the lamp filament will IC2 X1 IR RX TRIAC1 )tuo( A produce a rock steady level even at very low CABLE CS 33pF 4.7nF TIE brightness levels. Without the locking, the 1k 1.5M 1W LED2 lamp could have a slight flicker under phase 470Ω 220nF control. 4004 250V AC 1k 1W N LED1 D1 470 µF The infrared signal is detected by IC2, an amplifier/demodulator. This converts the reTO POWERBOARD TO POWERBOARD NEUTRAL SOCKET ACTIVE mote control’s modulated 38kHz pulses into digital levels that can be read by the IR monitor. Fig.5: all components are mounted on a single PC board which in turn Decoding into digital levels occurs at the rate is housed inside the powerboard case. Below is a same-size photo of set by the Timer 2 which is also locked to the the board from above. Note that the Triac (centre of picture) is bent mains frequency. over about 40° to allow it to fit inside the case. If the mains frequency happened to drift too far off 50Hz, then the remote control decoding would not operate correctly and would result in loss of remote control operation. Fortunately, the mains frequency is well within 5% of 50Hz and with this variation the remote control will still operate the Automatic Lamp Dimmer. The IR monitor signal is compared with known codes in the decoding section. Input pins 11, 12 and 13 select the particular code that is used, with four different codes available. When the selected, stored code is the same as controller senses this and so is provided with a reference the received remote control code, the brightness register position for the phase of the mains waveform. is altered in response to the particular button pressed on The zero-voltage negative-edge detector resets the bright- the remote control. For example, if slow down-dimming ness counter whenever the voltage is zero. After resetting, is selected, the brightness level register is increased to the brightness counter is incremented by 1 every 40ms from decrease lamp brightness. 0 up to 250. By the time the count reaches 250, some 10ms The comparator monitors both the brightness level reghas elapsed which is half the wavelength of the mains cycle, ister and the brightness counter. When they are equal, the the zero voltage crossing point for the second half cycle. comparator provides a pulse to drive the Triac gate. The 40ms brightness counter is clocked from timer 1, If the brightness level register is a low value, this value driven by a 20MHz crystal time base. It is important that will be equal to the brightness counter early in the mains the brightness counter reaches the count of 250 exactly at cycle to provide a bright lamp. If the brightness level register the zero crossing point. is a larger value, the value will be equal to the brightness This may not happen unless Timer 1 is locked to the counter later in the mains cycle and so the lamp will be mains. Without locking, the brightness counter could be dimmer. anywhere between 225 and 275, depending on the mains frequency. (Over time, the average mains frequency is held The circuit very accurately at 50Hz but in the short term can drift a Considering the complexity of the Automatic Lamp Dimlittle). mer operation, there is not too much in the actual circuit itself. We therefore lock the counter to the mains by adjusting This is because the complexity is all taken care of within the 100nF 250V AC 39Ω FR102 2.2k ACTIVE OF POWER BOARD CORD IC1 PIC16F628-20P 100nF 5040DACJ SHIELD CAN MADE FROM USB TYPE B SOCKET The modified Powertech powerboard before the insertion of the PC board. Here we’ve cut away the bus bars, removed part of the plastic moulding and drilled the holes for the two LEDs and the infrared signal bezel (far right). 30  Silicon Chip siliconchip.com.au And here’s another view of the PC board, this time at an angle to show the relative height of the components. In this shot, the two LEDs can be seen proud of the top of the 100nF capacitor (yellow, back of pic) to allow them to poke through the top of the powerboard and the “panel”. microcontroller (IC1). Apart from this IC, there is only the infrared decoder (IC2), a Triac, several diodes, a crystal and an inductor, plus a few resistors and capacitors. The Triac is connected between the mains Active and the lamp via an inductor (L1). This inductor, in conjunction with the 100nF 250VAC capacitor, provides suppression of electromagnetic radiation caused by the Triac switching. The inductor core is made from iron powder, which is lossy at high frequencies (above about 1MHz) and so prevents (or at least minimises) EMR from being radiated via the power wiring. Power for the circuit is derived from the mains supply via a 220nF 250VAC mains capacitor and a 1kW 1W resistor. The capacitor and resistor act as a current limiting impedance for the following zener diode, ZD1. The supply is derived in two steps. Firstly, supply is limited to 5V as diode D1 conducts when the mains voltage goes below the ground supply, pulling the anode of ZD1 to some 0.6V below the ground supply. This causes the zener to clamp the supply voltage to 5V (5.6V-0.6V). Secondly, when the mains swings above the ground supply, current can flow through the forward-biased zener diode and into the 470mF supply decoupling capacitor to top up the supply. Apart from the 470mF supply smoothing capacitor, both IC1 and IC2 have 100nF capacitors across their supply to provide high frequency decoupling. IC2 is further decoupled with a 100mF capacitor. Power for IC1 is supplied between pins 14 and 5. Pin 4 is a brownout input – should the supply drop below about 4V, the IC will be held reset until the supply voltage rises above the 4V level. This brownout reset ensures the microcontroller will operate correctly after the brownout has ended. Infrared code selection inputs are at the RB5, RB6 and RB7 pins. These pins can be left open or tied low with the linking to ground. When the microcontroller is reset after power is applied or after a brownout, the RB5, RB6 and RB7 inputs are pulled high via internal pull-ups within IC1. A check is made to determine whether the pins are all held high or if one is tied low via one of the links. This sets the remote control code that will operate the Automatic Lamp Dimmer. After this, the RB5, RB6 and RB7 input pull-up resistors are deselected and these inputs are set as low outputs. We need to set the RB5 – RB7 inputs as outputs to prevent them from floating and drawing excess current from the supply. The removal of the pull-up resistors from the inputs also removes the internal pull-up for RB0. This input detects the zero voltage crossing of the mains via a 1.5MW resistor and 4.7nF filter capacitor. The pull-up resistor is not required for the zero voltage detection since its value can vary from part to part, making the filter phase response too variable. This could produce an incorrect detection of the zero voltage crossing and causing faulty dimming characteristics such as flashing of the lamp. IC1 outputs RB1, RB2 and RB3 drive the gate of Triac1 via a 39W resistor and fast diode D2. Gate current is limited to around 50mA because of the resistor. The diode prevents the 0.7V present on the gate when the Triac is switched on from feeding back into IC1. Outputs RA1 and RA0 drive the “acknowledge” and “auto dim” LEDs respectively. The Acknowledge LED is driven with short bursts of high levels from RA1 and the 470W Now the new PC board has been placed and connections made back to the bus bars as required. What is not obvious here is that those connections should not just rely on the soldered joint; the wires should be twisted around the bus bars first. siliconchip.com.au July 2005  31 inside a shield to protect it as much as possible from external fields. Construction To open the powerboard, you’ll need a tri-wing screwdriver bit. They’re commonly available but if you don’t have one on hand, do what we did and grind the end of an old screw-driver blade into a triangle the right size. Don’t knock it: it works! resistor sets the current for sufficient LED brightness. The Auto Dimming LED is driven with slightly wider pulses and so can be driven with a lower current using the 1kW resistor. It is important that there is not too much current drawn from the supply as this is limited by that which can be delivered via the 220nF capacitor and 1kW resistor connecting to the mains Neutral. The 20MHz crystal X1 provides IC1 with an accurate clock signal for the timing requirements in the phase control driver and remote control functions. The 33pF capacitors provide the correct loading for the crystal to ensure reliable starting of the oscillator when power is applied. IC2 receives and demodulates the codes from the infrared remote control. It incorporates an amplifier and automatic gain control plus a 38kHz bandpass filter to accept only remote control signals. Upon detection of an infrared signal, it detects and removes the 38kHz carrier. The resulting signal is applied to the RB4 input of IC1. The high gain of IC2 makes it susceptible to interference from the switching of the Triac. The software has been planned so that the remote control signal is only monitored when interference is at a minimum. Interference does, however, affect the gain of IC2, which shuts down the gain as interference is detected due to its automatic gain feature. This gain reduction reduces infrared remote control range. To help prevent this reduction in gain, IC2 is housed MAINS CORD NEUTRAL (BLUE) The Automatic Lamp Dimmer is constructed on a PC board coded 10107051, measuring 96 x 35mm. It is mounted inside a 4-way power board. The power board provides us with a case, a power lead and mains plug plus the mains outlet. The power board is modified by blocking off three of the four mains outlets to make space for the dimmer circuitry. A cover plate is mounted over the blocked off sockets and secured with Nylon screws. Two LED indicators protrude through this cover plate. Begin by checking the PC board against the published pattern to ensure there are no shorts between tracks or any breaks in the copper. Repair these if necessary. First components to install are the resistors – use the colour code table as a guide to selecting each value and/ or use a multimeter to check each value. Solder in the socket for IC1, making sure the orientation is correct. Capacitors can also be inserted and soldered in place. The electrolytic types must be oriented with the polarity shown on the layout diagram, as must the diodes. Also ensure each is installed in its correct position. Install the Triac and crystal (the latter is not polarised). IC2 is mounted in the position shown with the leads bent forward and then upwards so that the lens section of the device is still vertical and located about 5mm back from the edge of the PC board. We made a shield for IC2 from a USB connector. Unclip and open up the rear of the USB socket’s shield and slide out the internal part. Bend back the rear flap on the shield to its closed position and insert the shield in place over IC2 and solder the mounting tabs to the PC board. The rear flap of the shield may need to be soldered in position since the bending process will have weakened the metal where it was bent. Inductor L1 is wound using 38 turns of 0.5mm enamelled copper wire, wound neatly, tightly and evenly around the core. This coil may produce a buzzing noise in the Auto- ACTIVE (FROM MAINS CORD VIA OVERLOAD SWITCH) (BROWN) EARTH (GRN/YEL) OVERLOAD SWITCH BRASS BUSBARS ACTIVE (BROWN) TOP OF POWER BOARD (UNDERSIDE VIEW) AUTODIMMER PC BOARD (UNDERSIDE VIEW) NEUTRAL (BLUE) EARTH WIRE (GREEN/YELLOW) Fig. 6: here’s how the new PC board fits into the modified powerboard, along with the connections required. Note that this diagram is for the Powertech (Jaycar MS4040) – other powerboards might be different. This diagram also gives you a good idea of where the busbars must be cut – a sharp pair of tinsnips is required here. 32  Silicon Chip siliconchip.com.au matic Lamp Dimmer, caused by the phase control method of dimming that produces sudden changes in current and movement in the wires. To prevent this happening, you can coat the windings in some epoxy resin before installing the core on the PC board. When the resin is dry, insert the wires into the PC board holes where shown and secure the toroid in place with the cable tie. Strip off the wire insulation near the underside of the PC board using a sharp hobby knife and solder the wires in place. Note that if you are using red-coloured enamelled wire, the insulation can be stripped with a hot soldering iron. Brass-coloured enamel will not strip under soldering iron heat and will need to be scraped off. LED1 and LED2 are mounted so that the top of each is 25mm above the top of the PC board. The longer lead of each LED is the anode. The tops should not protrude through the panel when assembled but be level with its surface. Leave the remote control code linking options for LK1 to LK3 open for the present. Modifying the powerboard We used a Powertech 4-way powerboard (from Jaycar Electronics) to house the project. Other powerboards may not have the same clearances nor setup inside. The powerboard requires modification in order for the PC board to fit inside. Firstly, you will need to open it up – most (as ours did) use tamper-resistant screws to stop you doing just that! The specified powerboard uses tri-wing screws, requiring a tri-wing screwdriver bit to open them. We didn’t have one so we used a bench grinder to grind an old screwdriver blade down to a triangular shape, then bent it over to make a handle. It’s rough . . . but it worked! Inside the power board you will see that there are brass bus bars to carry the Active, Neutral and Earth connections. The three far end sockets (those further away from the mains inlet cord) need to be cleared to make room for the PC board. This is done by cutting back the bus bars so that they are available for the first mains socket but not for the final three. Also, the plastic moulding will need to be removed to make space for the PC board components. This plastic can be removed with a small flat nosed set of pliers by twisting and breaking the plastic out from the case. The infrared receiver bezel is actually the front part of a red plastic neon bezel. Clip the power board casings together and drill out the hole in the end of the case to suit the bezel – it should be small enough so that the bezel is The powerboard we used for this project was a Powertech (Jaycar) MS4040. The PC board is designed to fit this one. siliconchip.com.au Parts List – Automatic Lamp Dimmer 1 PC board, code 10107051, 96 x 35mm 1 4-way mains power board (Powertech [Jaycar] MS4040 used in prototype) 1 pre-programmed “universal” infrared remote control (with channel numbers, volume and channel up and down plus mute and operate buttons) 1 133 x 51 x 3mm Perspex sheet (to cover three mains sockets) 1 powdered iron toroidal core, 28 x 14 x 11mm 1 B-type USB PC-mount socket (for the metal shield only) 1 20MHz crystal (X1) 4 M3 x 10mm Nylon screws 4 M3 nuts 1 all-plastic 240V red Neon Bezel (eg, Jaycar Sl-2630) 1 1.6m length of 0.5mm enamelled copper wire 1 150mm length of brown 10A mains wire 1 100mm length of blue 10A mains wire 1 200mm long cable tie Semiconductors 1 PIC16F628A microcontroller programmed with autolamp.hex (IC1) 1 BT137F 600V 8A Triac (Triac1) 1 infrared receiver decoder (IC2) 1 5.6V 1W zener diode (ZD1) 1 1N4004 1A 400V diode (D1) 1 FR102 fast diode (D2) 2 5mm high-intensity red LEDs (LED1,LED2) Capacitors 1 470mF 16V electrolytic 1 100mF 16V electrolytic 1 220nF 250VAC X2 polyester 1 100nF 250VAC X2 polyester 2 100nF MKT polyester 1 4.7nF MKT polyester 2 33pF ceramic Resistors (0.25W 1%) 1 1.5MW 1W 5% 1 2.2kW 1 1kW 1 470W 1 1kW 1W 5% 1 39W held in securely when the power board is screwed together. Use some Super Glue to secure the bezel to one half of the casing if it can be prised out of its hole. Two holes will be required for the LEDs in the top of the case. The cover plate is essential – it stops the unwary (or unknowing) trying to use the powerboard as a powerboard and possibly damaging components inside. Make up the cover plate to suit the powerboard you are modifying (use the photos as a guide) – it covers three of the four mains sockets. The two LED holes are also drilled into this plate. The plate is secured with Nylon screws, necessary as they provide insulation from the mains voltages inside the powerboard. We also recommend melting the Nylon screw ends over the nuts once installed to prevent them from becoming unscrewed. A hot soldering iron will do this. On the particular power board we used, there are two slotted holes at the rear, designed to allow the powerboard to be secured to a wall using screws. We recommend that July 2005  33 Capacitor Codes Resistor Colour Codes p p p p p p No. 1 1 1 1 1 1 Value 1.5MW 2.2kW 1kW 1kW 470W 39W 4-band Code (1%) 5-band Code (1%) brown green green gold (5%) red red red brown red red black brown brown brown black red gold (5%) brown black red brown brown black black brown brown yellow violet brown brown yellow violet black black brown orange white black brown orange white black gold brown Value 220nF 100nF 4.7nF 33pF mF IEC Code 0.22mF 220nF 0.1mF 100nF .0047mF 4n7 N/A 33p EIA Code 224 104 472 33 10107051 you fill the hole that is located beneath the dimmer A PC board with some Silicone sealant. This is because AUTO DIMMER there is a possibility (admittedly remote) that some thin metal object could be poked through the hole onto back of the PC, with possible dire consequences. Better to be safe than sorry, as mum used to say! A (out) SC The Active bus bar will need to be disconnected from the main active supply lead so that the dimmer circuitry can intercept the Active before the mains N outlet. The Earth lead connection may need to be relocated nearer to the mains socket. Make sure the Fig. 8: the full-size PC board pattern – use this to check wire is well soldered to the earth bus bar – it’s always the etching and drilling of commercial boards, or use it to best to make a mechanical joint (ie, wrap the wire photographically etch your own PC board. around the bus bar) which can hold by itself, then solder in place. 191 coding is that for a Philips TV set. If you are using a Wire up as shown and cut the neon bezel so that its length different remote control, try the codes listed for Philips will just reach the metal shield for IC2 when installed brand TV sets. into the case. The project is now electrically complete but Plug a 40W (or more) 240V lamp into the power board before you reassemble the power board, give it a thorough socket and plug the powerboard plug into a mains power visual check. socket. When you’re satisfied everything is as it should be, Check that the dimming can be set with the channel screw the two halves of the power board together with the up and down buttons and that slow dimming works. The tri-wing screws. Mute button should switch the lamp on and off. Check that Don’t be tempted to work on the next part of the project, the automatic dimming works by pressing the appropriate testing, before assembling the powerboard. Live wiring is button. If it does not work, check that the correct code has dangerous. been entered into the remote. Observe operation of the LEDs during these tests. Testing If the remote control also activates other items that are Before testing, you will need to set the remote control located in the same room where you will be using the to the appropriate coding. It is most unlikely that you will Automatic Dimmer, then the remote control coding will find any “universal” remote control which cannot be used need changing. with this project. The coding is changed by selecting one of the optional For the remote control we used, the “Big Shot 3 in 1” codes such as VCR1, SAT1 or SAT2. Generally, the SAT2 remote, the process is to press the SET and TV buttons selection is a good choice. This is selected by soldering a together and then enter the numbers 191. For other re- bridge for link 3 on the dimmer PC board. Before doing mote controls, the process may be slightly different. The this make sure (twice!) that the powerboard is unplugged from the mains so that it is safe to open. The hand-held remote will need to be programmed for the code selection. To select SAT2, press SET and SAT together and then enter the numbers 425. This number may be different for another type of remote control unit. If selecting SAT1 use the numbers 424 and for VCR1, use 336. Also the linking on the dimLK3 mer PC board will need to be changed. LK2 Note that for the VCR1 selection, the on and off LK1 function using the Mute button will not operate the Automatic Lamp Dimmer. Instead it will operate the mute in a TV set that works with the TV1 selection SOLDER LK1 FOR VCR1 REMOTE CONTROL LK2 FOR SAT1 CODING SELECTION on the remote. LK3 FOR SAT2 LEAVE ALL THREE OPEN FOR TV1 This feature is called punch-through, where selecFig.7: this view of the copper side of the PC board shows the three tions that do not have a mute feature are operated by the TV code. links which set the correct infrared decoding (see text). SC N A AUTO DIMMER SC 10107051 A (out) 34  Silicon Chip siliconchip.com.au