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Remote Volume Control & Preamplifier Module This up-to-date control module works with any universal infrared remote and features a blue LED readout and an optional rotary encoder. Its ability to both attenuate and amplify means that it can operate as a simple volume control or as a highperformance stereo preamplifier! S INCE THE PUBLICATION of our previous general-purpose remote volume control project (June 2002), a number of readers have requested a comparable unit with digital, rather than analog, attenuation. In other words, they want to dispense with the potentiometer, citing the short operational life and poor channel-tochannel tracking of these mechanical components. For those that haven’t seen the 24  Silicon Chip earlier project, a dual-gang motorised potentiometer was driven by a microcontroller to selectively attenuate the incoming audio signal. The advantage of this approach is simplicity and (depending on the pot used) relatively low cost. We used this method again in the Studio Series Preamplifier Control Module (April 2006), where we showed how it is possible to achieve both reliability and high performance using a more expensive motorised potentiometer. Nevertheless, we con-tinued to receive requests for a digitally attenuated version – so here it is! Now you’ve no excuse not to do away with that noisy old pot and upgrade to this state-of-the-art digitally controlled module – which should never wear out! Main features The Remote Volume Control & Preamplifier Module allows volume and balance adjustments to be made with any universal infrared remote control. Adjustments can also be made via an optional up-front rotary encoder. The encoder we’ve selected has 20 detents per revolution and a positive, professional feel. The volume and balance levels are displayed on a blue or red 2-digit read­ out, which can be set to “go blank” shortly after each adjustment for less siliconchip.com.au Pt.1: By PETER SMITH Also featured is a new, low-noise power supply module that includes its own on-board transformer. If the long slim board layout doesn’t suit your case, then the PC board has been designed so that you can slice off the transformer and juggle the two modules about to your heart’s content. But wait – there’s more! For those who already have a suitable chassis-mount transformer, we’ve also included a version of the supply without the transformer to save you having to cut the board apart in the first place! OK, so this new design uses a digital rather than analog volume adjustment method. To understand how this works, let’s look briefly at a basic attenuator and then compare this to the internals of the PGA2310. Digital control invasive operation. Muting is also supported via remote control. Due to its universal nature, the module can be used in-line in just about any hifi audio system. For example, it could be inserted between your CD/ DVD player and power amplifier – and would be ideal for use with several of our past audio amplifier projects, such as the SC480 (Jan./Feb. 2003) and the Studio 350 (Jan./Feb. 2004). The design is essentially a 2-chip solution, with the audio side handled by a high-performance Burr-Brown PGA2310 stereo audio volume control IC. An Atmel ATmega8515 microcontroller manages the user interface, which comprises the rotary encoder, two optional selection switches, an infrared remote control receiver and two 7-segment displays. It also communicates with the PGA2310 over a 3-wire serial interface to set the device’s volume levels. The two displays mount on their own small PC board and are wired back to the module via ribbon cable. All other components mount on the main board, which is designed to fit directly behind the front panel of a metal enclosure. This arrangement affords flexibility and simplifies construction for the majority of case assembly options. siliconchip.com.au Digital attenuation of an audio signal is quite straightforward in concept. In its simplest form, an attenuator might consist of resistive voltage divider whose elements can be selectively switched in and out of circuit under digital control. A basic representation of such an attenuator appears in Fig.1. With neither of the switches (S1 & S2) closed, the attenuation of the circuit can be expressed as: VOUT/VIN = (RB1 + RB2 + RB3)/(RA + RB1 + RB2 + RB3). Applying a digital logic “high” level to the control input of either switch causes it to close, bypassing a branch of the string. For example, if S1 closes, resistors RB2 & RB3 are bypassed, so the expression becomes: VOUT/VIN = RB1/(RA + RB1). As you can see, the circuit has three possible states or levels of attenuation. To increase the number of states, it’s just a matter of adding more resistors and switches. For audio use, the resistor values would be chosen so that each state change results in a logarithmic change in the attenuation level. Why the op amp? It acts as a buffer, isolating the circuit from output loading effects and generating a constant output impedance regardless of attenuation level. Programmable gain As mentioned, this design is based around the PGA2310 IC from BurrBrown (Texas Instruments) – see Fig.4. It integrates a digitally programmable attenuator that operates in much the same way as our example in Fig.1. However, this device is a little different in that the gain of its op amp is also digitally programmable. This means that it can be programmed to operate as an attenuator or an amplifier. Its overall adjustment span is 127dB, ranging from -95.5dB to +31.5dB in 0.5dB steps. Gain changes are effected during audio signal zero crossings, eliminating the audible “clicks” that typically occur without this feature. Two identical channels are included, labelled (not surprisingly) “left” and “right”. The level of each channel is set by a 16-bit serial data word that is transferred via the device’s digital Fig.1: this simplified circuit represents the basics of a digitallycontrolled analog attenuator. Two analog switches (S1 & S2) are opened and closed under digital control to select the inputto-output attenuation level of the circuit. February 2007  25 26  Silicon Chip siliconchip.com.au Fig.2: the complete circuit diagram for the module, minus the display board. All analog functions are handled by the PGA2310 volume control chip (IC1), while microcontroller IC2 deals with the user interface. When a volume change is requested by the user – either via the infrared receiver (IC3) or the rotary encoder – the microcontroller interprets the request and sends the new data down a serial pipe to IC1. interface. The PGA2310 was designed specifically for professional audio work, boasting high dynamic range and very low noise and distortion. How it works We’ve endeavoured to keep construction as simple as possible, hence the use of just three ICs (see Figs.2 & 3). The microcontroller (IC2) handles all aspects of the user interface, which comprises the rotary encoder, infrared receiver IC3, the LED displays and pushbutton switches S1 & S2. In response to user commands, the micro sends the desired volume level to the volume control chip (IC1) via a “3wire” serial interface. The serial interface consists of the signal lines SDI (Serial Data In), SDO (Serial Data Out), SCLK (Serial Clock) and CS (Chip Select). Each serial data transfer from the micro to the PGA2310 (IC1) consists of a complete 16-bit word, comprising one byte for each channel. Those interested in the specific timing details will find them in the relevant datasheet, available from www.ti.com. The micro can immediately mute both channels by driving the MUTE input of IC1 low. It can also determine how a new gain setting is applied to the device’s control registers by controlling the ZCEN input. If this input is high, the gain is updated on the second zero crossing of a channel’s input signal. This minimises audible glitches on the output. Conversely, if ZCEN is low, the update is performed as soon as it’s received. Note that with high volume levels and no input signal, it may well be possible to hear clicks when altering the volume level. This occurs because the PGA2310 waits only 16ms for the two zero crossings and if not detected, the new gain setting will take effect with no attempt to minimise audible artifacts. siliconchip.com.au The analog interface side is extremely simple, consisting of just a handful of resistors, capacitors and RCA sockets (CON4-CON7). The left and right channel inputs are arranged so as to be as far apart as practically possible, with obvious benefits in the channel crosstalk performance (see performance panel). As shown, the signal inputs are capacitively coupled to prevent DC currents from flowing in the PGA2310’s attenuator circuits. The 100W series resistors provide a small amount of protection from input over-voltages and also interact with 100pF capacitors to ground to filter out high-frequency noise. Note that larger resistor values cannot be used here because they would degrade the PGA2310’s distortion performance. On the output side, 100W resistors isolate the PGA2310’s drivers from cable and amplifier input capacitance, thereby ensuring stability. They also provide a measure of protection from short-circuit signal lines. Again, coupling capacitors prevent DC currents flowing in the output circuit. Keeping noise at bay Apart from minimising external logic, the use of a large 40-pin microcon- Fig.3: there’s not a lot to the display board – just two commoncathode 7-segment displays and a 20-way header socket. Resistors in series with each segment (on the main board) limit LED current to less than 5mA; an important requirement, as IOH current for ports A & C must not exceed 100mA in total! Fig.4: this block diagram shows the internal functions of the PGA2310 volume control IC. Both the input attenuation level and op amp gain are digitally controlled. The attenuation/gain levels are set via the on-board serial control port logic, which receives its data from the microcontroller. February 2007  27 Fig.5(a): a basic representation of a rotary encoder. This also shows how the switch inputs are pulled up via resistors internal to the microcontroller. The program in the micro filters out switch contact bounce and interprets the ‘A’ and ‘B’ signals to detect shaft rotation and direction. troller also allowed us to dispense with the need for display multiplexing, as each LED segment can be driven by one port pin. This is an important element of the design because it eliminates a potential source of switching noise. The other area that requires careful design to keep noise at bay is the power supply. As you can see, we’ve used RC filters comprising 10W resistors and 1000mF capacitors on the ±15V rails to reduce noise to a minimum. Strictly speaking, these are not required when the module is powered from the supply described here. However, they ensure consistent performance if the Fig.5(b): the two out-of-phase switch signals from the rotary encoder generate a 2-bit Gray code, defining one complete electrical cycle. Some encoders will have more than one detent per cycle unit is to be powered from the auxiliary outputs of a power amplifier’s supply, for example. Conducted noise from the microcontroller is reduced by the inclusion of an LC filter in its 4.7V supply, made up of a 100mH choke (RFC1) and an associated 100mF capacitor. In additional, digital ground is connected to analog ground at one point only – ie, at the power input connector (CON1). To ensure that this strategy is effective, you must use heavy-duty hook-up wire for the power supply wiring, as described in Pt.2 next month. Schottky diodes (D1-D3) in series Performance • • Frequency response......................................... flat from 10Hz to 150kHz • • • • • • • • • Input impedance............................................................................ ~10kW Maximum input signal...................... 9.7V RMS (0dB gain), 250mV RMS (+31.5dB gain) Output impedance........................................................................... 100W Harmonic distortion .......................................typically .002% (see Fig.9) Signal-to-noise ratio..............................-120dB (20Hz-22kHz bandwidth) Channel crosstalk.............................. -126dB <at> 1kHz, -123dB <at> 10kHz Adjustment range.............. 127dB (-95.5dB attenuation to +31.5dB gain) Step size....................................................... 0.5dB or 1.5dB (selectable) Gain matching............................................................................. ±0.05dB Display resolution........................................................................... 1.5dB Note: except where noted, all measurements were performed with a 600mV RMS input signal at 0dB (unity) gain with the output driving a 50kW load. For crosstalk measurements, the non-driven input was back-terminated into 600W. 28  Silicon Chip with all inputs help to reduce the chances of blowing something up if the input wiring is accidentally reversed. With the excellent dynamic range of the PGA2310, the loss of 300mV or so in the supply rails has little effect on performance. Despite this protection, it’s still possible to make a mistake – such as feeding +15V into the +5V input. In this case, ZD1 will conduct and rapidly collapse the rail, while sending up smoke signals. Assuming that you spot these early on, disaster may well be averted! No special interfacing logic is required for the switches or rotary encoder, because the entire switch debouncing and decoding sequence is carried out in firmware. The same applies to the output of the infrared receiver module (IC3). Its serial data stream is interpreted in line with the Philips RC5 infrared protocol, using an accurately timed, high-speed sampling algorithm to ensure excellent long-range performance. Encoder basics If you’ve never used a rotary encoder, you may be wondering how they work. The simplest encoders consist of a multi-lobed cam that is used to operate two microswitches (Fig.5a). When the shaft connected to the cam is rotated, one of the switches opens and closes in advance of the other, depending on the direction of rotation. This generates a 2-bit Gray code at the switch output terminals, which can be interpreted by a microcontroller or other digital logic to determine shaft position and direction of rotation (see Fig.5b). siliconchip.com.au Fig.6: the low-noise power supply uses common 3-terminal regulators and features an on-board toroidal transformer. This transformer generates less radiation than larger chassis-mount units so it should be possible to build the whole lot into a relatively small case without having problems with induced mains noise. As you can see, the four Gray code states describe one complete cycle, with the detents occurring when both switches are off. The encoder used in this project has 20 cycles (or “pulses”) and detents per revolution, so the cycle repeats every 18° of rotation. Its direction of travel is indicated by the phase of the two signals, which are always 90° apart. The timing diagram applies to most 2-bit encoders that utilise one detent per cycle (equal pulses and detents per revolution). In fact, the microcontroller program expects this configuration, so if you’re thinking of sourcing an alternative part, be sure that it meets this criteria. Also, get a unit with 20 or more detents – any less will result in unnecessary knob winding! Many other configurations are available; two and four detents per cycle are common. For example, an encoder specified with 4 cycles/rev and 16 detents/rev has 4 detents/cycle and is unsuitable for use here – it would take four clicks (1/4 revolution) to make a single change to the volume or balance! Note also that some encoders have built-in switches. Such a device would be ideal for this project, because it would be possible to wire the BALANCE switch input (at CON3) to the encoder’s switch terminals, thereby dispensing with the need for a separate switch to select balance adjustment mode. Low-noise supply To ensure the best possible performance, we’ve designed a separate, low-noise power supply to match the Remote Control & Preamp module. It provides regulated ±15V and +5V outputs and could be used with a variety of other audio projects. As mentioned above, it even includes an on-board toroidal transformer to further simplify construction. As shown on the circuit diagram (Fig.6), the transformer’s two 15VAC secondary windings are connected in siliconchip.com.au February 2007  29 Fig.7: follow this diagram when assembling the control board. Fig.8: it should only take a few minutes to assemble the display board. Note how the decimal points go at the top of the readouts, rather than at the bottom. series to form a 30VAC centre-tapped configuration. Note the fuses in the secondary outputs – these are included because the voltage regulators’ builtin current limiting may be too high to protect a small 10VA transformer in the event of an output overload. Diodes D1-D4 and two 2200mF capacitors rectify and filter the secondary output to create ±21V DC (nominal) rails. The following LM317 and LM337 adjustable regulators then generate the complementary positive and negative supply rails. Their outputs are programmed to ±15V by virtue of the 100W and 1.1kW resistors connected to their “OUT” and “ADJ” terminals. We’ve used adjustable regulators in this design because the “ADJ” terminals can be bypassed to ground to improve ripple rejection, which we’ve done using 10mF capacitors. The associated diodes (D6 & D9) provide a discharge path for the capacitors should an output be accidentally shorted to ground. Two reverse-connected diodes Table 1: Resistor Colour Codes (Control Board) This is the completed display PC board assembly. The LED readouts plug into two single in-line header strips. 30  Silicon Chip o o o o o o o o o o Value 100kW 10kW 4.7kW 1.1kW 1kW 560W 330W 100W 10W 4-Band Code (1%) brown black yellow brown brown black orange brown yellow violet red brown brown brown red brown brown black red brown green blue brown brown orange orange brown brown brown black brown brown brown black black brown 5-Band Code (1%) brown black black orange brown brown black black red brown yellow violet black brown brown brown brown black brown brown brown black black brown brown green blue black black brown orange orange black black brown brown black black black brown brown black black gold brown siliconchip.com.au Fig.9: the noise and distortion sits at around .002% with a 600mV input signal. The datasheets quote a smaller THD+N figure but use a much larger input signal – so we’ve plotted a second line to show the difference with a 5V input signal. Watch the orientation of the diodes, IC sockets, polarised capacitors and shrouded headers (CON8 & CON9). Use only the resistor values specified for the LED displays – lower values could lead to damage to the microcontroller ports. (D7 & D10) across the output prevent their respective rails from being driven to the opposite polarity (eg, if a regulator fails). A 7805 3-terminal regulator (REG4) is used to generate the +5V rail. To reduce power dissipation in REG4, a second fixed regulator (REG3) is positioned “upstream” to reduce the DC input from 21V to 15V. While we could have just added a series resistor or even a transistor-based pre-regulator to achieve similar results, this arrangement is inexpensive and includes the regulator’s protection features in the case of an overload. Because the +5V supply draws power from only the positive side of the unregulated DC rail, a 390W resistor (R1) across the negative input is included to help balance the rails, so that they decay at similar rates at power off. Fig.10: the frequency response is – well – flat! Construction We’ll assemble the main PC board (code 01102071) first – see Fig.7. Begin by installing the three wire links using 0.7mm tinned copper wire, then install the resistors. Note that the 330W resistor values adjacent to CON9 on the overlay diagram are for blue displays only. If you’ve decided to use red displays instead, then substitute 560W values for 16 of the 330W parts as indicated. All of the diodes (D1-D5 & ZD1) can go in next, taking care to orient their cathode (banded) ends as shown. That done, all remaining components can be installed siliconchip.com.au Fig.11: channel-to-channel crosstalk could hardly be better. The left & right signal inputs are located at opposite ends of the chip – and we took maximum advantage of this in the PC board layout. February 2007  31 Fig.12a: follow this diagram when assembling the power supply board. Most constructors will not want to cut the board into two sections, so terminal blocks CON1 & CON4 won’t be required. The transformer should be secured to the PC board via the central mounting hole before its pins are soldered. Below: this view shows the fully-assembled power supply board. Don’t forget to fit the cover over the mains fuse. Table 2: Capacitor Codes in order of height, with attention to the following points: • Be sure to insert the 1000mF and 100mF electrolytic capacitors around the right way, following the “+” markings on the overlay. The 47mF units are non-polarised and can go in either way. • The notch in the IC sockets must match that shown on the diagram, as must the polarising notch in the two shrouded headers (CON8 & CON9). 32  Silicon Chip Do not plug the ICs into their sockets until after the power supply has been cabled in and tested (see the “Testing” section in Pt.2 next month)! • The terminal blocks (CON1-CON3) and RCA connectors (CON4-CON7) must be seated squarely on the PC board surface before soldering. • Seat the crystal (X1) all the way down on the board before soldering. Once in place, connect its metal case to ground via a short length of tinned copper wire (see photo). • The lead length and bend of the two LEDs and infrared receiver (IC3) Value mF Code IEC Code EIA Code 220nF 0.22mF 220n 224 100nF 0.1mF 100n 104 100pF NA 100p 101 22pF NA   22p   22 can be determined by trial fitting the assembly into its intended position. Display board There’s not a lot to the display board – just a socket for the two displays and a 20-way header (see Fig.8). The socket can be made by cutting down a longer single-in-line (SIL) header strip into two 10-pin sections. Make sure siliconchip.com.au Fig.12b: this alternative version of the power supply board is available for those who prefer to use a chassis-mounted toroidal transformer. This board is essentially an upgrade to the low-noise supply featured in the October 2005 issue and will run cooler than its predecessor thanks to larger heatsinks. This view shows the mounting arrangements for the heatsinks and the regulators at one end of the PC board. Be sure to fit the heatsink tabs through their matching board holes, so that the heatsinks cannot touch each other. that these are sitting perpendicular to the PC board before soldering. When plugging in the display modules, note that the decimal points go at the top, not the bottom of the readout. Also, make sure that you’ve got the polarising notch of the header (CON10) facing inwards towards the displays. Power supply The power supply can be constructed in a number of different ways. If you’ve elected to build the version with an on-board transformer, then you have the option of separatsiliconchip.com.au ing the transformer section from the remainder of the board before commencing construction (see Fig.12a). Most constructors will not need to do this – check your chassis layout for compatibility before reaching for a hacksaw! If using a chassis-mount transformer, then you may optionally choose the second (smaller) power supply board, which omits the on-board transformer, fuses and associated connectors (Fig.12b). However, the following text assumes that you are assembling the on-board transformer version. As before, install all of the low- Fig.13: here’s how to assemble the regulators to their heatsinks. The 7805 regulator (REG4) presents a special case; its screw should be inserted from the opposite side to that shown so that the screw head isn’t obscured by REG3’s heatsink. The PC board holes for the heatsink tabs should be drilled to 2.5mm. If this proves to be marginally too small to accept the tabs, you can use a jeweller’s file to remove just enough of the tabs to get a neat fit. The 390W 5W resistor should be mounted about 2mm off the PC board. profile components first, starting with the single wire link. Note that we’ve specified a singlepiece fuseholder assembly with cover February 2007  33 Parts List 1 main PC board, code 01102071, 109 x 78mm 1 display PC board coded 01102072, 49mm x 34mm 1 rotary encoder, 20 pulses/ detents per rotation (Altronics S-3350) (optional, see text) 1 2-way 5mm/5.08mm pitch terminal block (CON2) 2 3-way 5mm/5.08mm pitch terminal blocks (CON1, CON3) 1 10-way boxed header (CON8) (Altronics P-5010, Jaycar PP1100) 2 20-way boxed headers (CON9), (CON10) (Altronics P-0144A) 2 PC-mount RCA sockets, red insert (CON4, CON5) (Altronics P-0144A) 2 PC-mount RCA sockets, black insert (CON6, CON7) (Altronics P-0145A) 1 40-way or 2 x 32-way 2.54mm SIL header socket(s) (Altronics P-5400, Jaycar PI-6470) 1 7-way 2.54mm SIL header (JP1JP3) 3 jumper shunts 1 100mH choke (RFC1) 1 16-pin gold-plated IC socket 1 40-pin IC socket 4 M3 x 6mm pan head screws 4 M3 x 10mm tapped spacers 0.7mm diameter tinned copper wire for links Semiconductors 1 PGA2310PA stereo volume control IC (IC1) (Farnell 1212339) 1 ATmega8515-8P (or –16P) microcontroller (IC2) (Jaycar ZZ-8765) programmed with DAVOL.HEX 1 TSOP4838 (or equivalent) infrared receiver module (IC3) for the mains fuse (see parts list) – so be sure to fit this in the correct (F1) position. The other two fuses (F2 & F3) use low-cost fuse clips. Position the small retaining lug on each clip towards the outer (fuse end) side; otherwise proper fuse installation will be impossible. The 390W 5W resistor mounts vertically (see photos) and should sit about 34  Silicon Chip (Altronics Z-1611, Jaycar ZD1952, Farnell 491-3190) 1 4MHz crystal, HC49S package (Y1) (Altronics V-1219) 3 1N5819 Schottky diodes (D1D3) 2 1N4148 small-signal diodes (D4, D5) 1 1N4735A 6.2V 1W zener diode (ZD1) 2 127mm common-cathode 7-segment LED displays, blue (Jaycar ZD-1856) or red (Jaycar ZD-1855, Altronics Z-0190) 2 3mm red LEDs (LED1, LED2) Capacitors 2 1000mF 16V PC electrolytic 3 100mF 16V PC electrolytic 4 47mF 35V/50V non-polarised PC electrolytic (max. 8mm dia.) 4 100nF 50V monolithic ceramic 2 100pF ceramic disc 2 22pF ceramic disc Resistors (0.25W 1%) 3 100kW 16 560W (red displays) 1 10kW 1 330W 2 4.7kW 16 330W (blue displays) 4 1kW 10 100W 1 560W 2 10W Additional items 2 20-way IDC cable-mount sockets (Altronics P-5320, Jaycar PS-0986) 20-way IDC ribbon cable (Altronics W-2620) Pushbutton switch (optional – see text) Universal remote control (see text) Power Supply 1 PC board, code 01102073, 168 x 61mm (on-board transformer) 2mm proud of the PC board surface to aid in cooling. If the board has been cut into two parts, then you’ll need to run an insulated wire link between points ‘A’ & ‘B’ to reconnect the ground end of this resistor back into circuit. On a similar note, terminal blocks CON1 & CON4 need only be installed if the board was cut apart. Due to its size and weight, the –or1 PC board, code 01102074, 80 x 61mm (off-board transformer) 4 Micro-U 19°C/W TO-220 heatsinks with tabs (Altronics H 0637, Jaycar HH-8504) 2 3-way 5mm/5.08mm terminal blocks (CON1, CON2) 1 2-way 5mm/5.08mm terminal block (CON3) 4 M3 x 10mm tapped spacers 8 M3 x 6mm pan head screws 4 M3 nuts & flat washers 0.7mm diameter tinned copper wire for link Heavy-duty hook-up wire for lowvoltage wiring Heatsink compound Semiconductors 1 LM317T adjustable positive regulator (REG1) 1 LM337T adjustable negative regulator (REG2) 1 7815 +15V regulator (REG3) 1 7805 +5V regulator (REG4) 11 1N4004 diodes (D1-D11) Capacitors 2 2200mF 25V 105°C PC electrolytic 2 100mF 16V 105°C PC electrolytic 3 10mF 16V 105°C PC electrolytic 1 220nF 50V metallised polyester (MKT) 2 100nF 50V metallised polyester (MKT) Resistors (0.25W 1%) 2 1.1kW 2 100W 1 390W 5W 5% Additional items for on-board transformer version 1 15V+15V 10VA PC-mount toroidal transformer (Altronics M-4330) transformer must be firmly attached to the board using an appropriate self-tapping screw via the provided mounting hole before its pins are soldered. If this is done in reverse order, the PC board pads may delaminate! You have been warned. Leave the four regulators (REG1REG4) until last. These must be attached to TO-220 heatsinks before siliconchip.com.au 1 M205 250VAC PC-mount fuseholder w/cover (F1) (Altronics S-5985) 4 M205 fuse clips (F2, F3) (Altronics S-5983, Jaycar SZ2018) 2 3-way 5mm/5.08mm terminal block (CON4, CON5) 1 100mA 250VAC M205 slow-blow fuse (F1) 2 250mA M205 slow-blow fuses (F2, F3) Self-tapping screw for transformer mounting Mains connection hardware to suit Additional items for off-board transformer version 1 15V+15V 20VA (or larger) toroidal transformer (eg, Jaycar MT-2086) Mains connection hardware to suit Notes Note 1: the low-voltage version of the microcontroller is also compatible with this project and is available from Futurlec at www.futurlec.com. au, part number ATmega8515L-8PI (or –8PU). Note 2: The 100mA and 250mA slow-blow fuses can be had from Wiltronics Research, stock Nos. FU0312 & FU0314. Check them out at www.wiltronics.com.au. Rockby Electronic Components also carry the fuses, stock Nos. 14740 & 14743 – see www.rockby.com.au for more details. Note 3: to avoid assembly difficulties and ensure long-term reliability, all the 3-terminal regulators (REG1-REG4) used in the power supply should be recognised name-brand devices, such as On Semiconductor/Motorola, STMicroelectronics, National Semiconductor or Fairchild. being installed on the PC board. First, smear a thin film of heatsink compound to both the rear (metal) area of each device as well as the mating areas of the heatsinks. That done, fasten them to the heatsinks using M3 screws, nuts and washers as shown in Fig.13 but don’t fully tighten the screws just yet. Note that insulating pads should siliconchip.com.au Universal Infrared Remote Controls The volume control module is designed to work with most universal (“onefor-all”) infrared remotes. It recognises the RC5 protocol that was originally developed by Philips, so the remote must be programmed for a Philips (or compatible) appliance before use. Most universal remotes are provided with a long list of supported appliances and matching codes. To set the remote to work with a particular piece of gear, it’s usually just a matter of entering the code listed for the manufacturer (in this case, Philips), as detailed in the instructions. You’ll also note that different codes are provided for TV, CD, SAT, and so on. This allows two or more appliances from the same manufacturer to be operated in the same room and even from the same handpiece. This multiple addressing capability can be useful in our application, too. Normally, we’d program the remote to control a TV, as this works with the control module. But what if you already have a Philips TV (or a Chinese model that uses the RC5 protocol)? Well, in this case, you’d simply use a CD or SAT code instead – the control model can handle any or these! Let’s look at an example. To set the AIFA Y2E remote to control a Philips TV, you’d first press and hold “SET” and then press “TV”. This puts the remote in programming mode, as indicated by the red LED, which should remain illuminated. Now release both keys and punch in one of the listed Philips TV codes. For this project, code 191 works well. The red LED should now go out and the remote is ready for use. All universal remotes can be programmed in a similar manner but when in doubt, read the instructions! If the first code listed doesn’t work with the control module, then try another. Once the remote has been programmed, the control module must be set up to recognise the particular equipment address that you’ve chosen (TV, CD, SAT, etc). Details on how to do this are in the setup and testing section. Although this project should work with any universal remote, we’ve tested the following popular models: AIFA Y2E (Altronics A-1013), AIFA RA7 (Al­tronics A-1009) and BC3000 (Jaycar AR-1710, pictured). For all these models, the setup codes are as follows: TV = 191, CD = 651 (but not for BC3000 remote), SAT1 = 424 and SAT2 = 425. Note that the “mute” button doesn’t work for all codes and in the case of the AIFA Y2E, is missing anyway! In these cases, you may be able to use the “12” or “20+” buttons instead. not be used here, as they will impede heat transfer. Now slip each assembly into place in its PC board holes, taking care not to mix up the different regulator types. The tabs of the heatsinks should fully engage the holes in the PC board, such that all of the heatsink edge contacts the PC board surface. You may find that the PC board holes are fractionally too small to allow this to happen – if this is the case, use a jeweller’s file to remove just enough of the tab to get a neat fit in the holes (see photo). Finally, push the regulators all the way down the slots in the heatsinks and then tighten up the screws. The regulator leads can now be soldered, taking care that the assemblies remain in place when the board is turned over. Note that you’ll find it easier if the devices are mounted in a specific order, as follows: REG2 first, then REG1, REG3 & REG4. That’s all we have space for this month. Next month, we will complete the construction and describe the setSC up and test procedures. February 2007  35