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Pt.2: By PETER SMITH Remote Volume Control & Preamplifier Module Second article completes the construction & gives the set-up procedure W E’VE PRESENTED the Remote Control & Preamplifier project as a stand-alone module because we believe that many constructors will want to build it into an existing case. It is designed to fit flush behind a front panel, hence the LEDs and the rotary encoder are located along the front edge of the board. However, all of these devices can be mounted independently on a panel and wired back to the PC board via short flying leads if desired. Note that if the infrared receiver includes an external metal shield (see photo), then steps must be taken to ensure that it is insulated from the chassis. We suggest a short strip of insulation tape on the inside of the front panel, with a hole cut out to match the hole in the panel. Do not rely on the paintwork to provide insulation! The display board should be mounted to the right side or above the main 34  Silicon Chip board (ie, away from the audio section) on standoffs behind an appropriate cutout. Additional header sockets (or cut-down 40-pin IC sockets) can be stacked vertically to increase the display height for a flush fit. Both the red and blue displays look great with tinted filters! As mentioned earlier, three different power supply configurations are possible. You could also power the unit from an existing regulated DC source if available. The minimum requirements are: ±15V <at> 20mA and +5V <at> 120mA. Note that the two (analog & digital) supplies must share a common ground. This means that if they’re located on physically separate PC boards, their grounds must be cabled separately to the single “GND” input at CON1. Mains wiring As usual, all 240VAC wiring must be carried out in a safe and professional manner, meaning that we’re assuming that you already have the relevant expertise or can obtain assistance from someone who has. Most importantly, the assembly must be housed in an earthed metal enclosure. The mains earth must be properly connected to this chassis and this can be achieved via a double-ended 6.3mm spade lug fastened securely to the base with an M4 x 10mm screw, shakeproof washer and two nuts – see Fig.16. A basic wiring layout is shown in Fig.14. The mains section of the wiring will obviously need to be amended if the module is to coexist with a power amplifier, which will at least share the mains input socket and power switch. Note that if using a separate, chassismounted transformer, alternative arrangements must be made for mains fusing. This is best achieved by using an IEC socket with an integral fuse. Once the mains wiring has been completed, go back and check that each connection is secure and well insulated. If necessary, use heatshrink siliconchip.com.au tubing to completely cover any exposed terminations. That done, use your multimeter to check continuity between the earth pin of the mains plug and any convenient point on the chassis that is devoid of paint. This check must be repeated later when the case is assembled. At that time, use your meter to check that all panels of the case are earthed – without exception! Low-voltage wiring As a first step, disconnect the mains cord to prevent mishaps while working under the hood. You can then complete the assembly by running all the low-voltage wiring. If a separate transformer has been used, its two secondary (15VAC) windings must be terminated at the transformer input (CON1) of the power supply board. Twist the wires together and keep them as short as possible to reduce radiated noise. Next, connect the +15V, -15V & GND outputs at CON2 and +5V at CON3 on the power supply to the matching inputs at CON1 & CON2 of the Remote Volume Control & Preamp module. Note that the GND output at CON3 on the power supply is not used! Use only heavy-duty hook-up wire for the job. Take great care to ensure that you have all of the connections correct – a mistake here may damage the control module. We suggest four different cable colours to reduce the chances of a mistake! If you wish to be able to control left/ right balance from the front panel, then you’ll also need to install a pushbutton switch. This will enable you to use the rotary encoder for both volume and balance adjustments. The terminals of the switch are simply wired between the BALANCE and GND inputs at CON3. Having said that, balance adjustment is a rare requirement after initial setup (which would be done via remote control), so most constructors will not need this switch. The module also provides a second switch input at CON3 labelled CHANNEL. This is intended for a possible future multi-channel upgrade and should not be connected, as it currently has no function. Use good quality shielded audio cable for all the audio connections. Terminate one end of the cables in RCA plugs for connection to the control module’s inputs and outputs. Dependsiliconchip.com.au Fig.14: follow this basic diagram when hooking up your module. Use heavyduty hook-up wire for all of the low-voltage power supply connections. For the mains side, use only mains-rated cable and be sure to keep if well away from the low-voltage side. A few strategically placed cable ties will keep everything in position, even if a wire should happen to come adrift! ing on your requirements, you may wish to fit chassis-mount RCA sockets at the other end and mount these on the rear of your case. Finally, you’ll need to make up the cable for the main board to display board connection. This is simply a length of 20-way IDC ribbon cable terminated with 20-way plugs at either end (see photos). We used a 12cm length for the prototype but we expect that if could be at least twice as long without causing any problems. Avoid routing the cable close to the analog section of the control module. green/yellow earth wire from the pad just to the left of the rotary encoder to the chassis earth point. This solidly earths the body of the encoder to protect the microcontroller from static discharge. To earth the audio ground, run another wire from the chassis earth point Earthing So far, you should have just two wires connected to the chassis earth point – the mains earth wire from the IEC socket and a second wire to the “E” input (at CON5) of the power supply. Now run an additional mains-rated If your infrared receiver module has a metal shield like this one, then be sure to insulate it from the front panel as described in the text. March 2007  35 Fig.15: the 2-digit readout displays volume & balance on a 0-85 scale & flashes an indicator when muted. Note that the channel select mode is for a possible future upgrade and can be ignored at present. to the free pad situated between CON5 & CON6 on the control module, again using mains-rated green/yellow wire. Both earth wires should fit into a single spade crimp terminal to mate with the free end of the chassis-mounted lug. This earthing method will reduce the chances of creating an audible “earth loop” in your system but success is not guaranteed! For example, if your power amplifier also earths the audio signal, an earth loop will exist once the two are hooked together. This may or may not be a problem. If you notice more hum in your audio system after connecting the preamp, then try disconnecting the earth wire to the control module. Never, ever, disconnect the mains earth from the chassis! Testing Before applying power for the first time, bear in mind that the mains input end of the power supply circuit board is live! Accidentally placing a finger under the board or contacting the mains input terminal block (CON4) screws might well prove fatal! Therefore, it is important that the power supply board is securely Table 1: jumpers must be installed on both JP1 & JP2 during the initial setup. 36  Silicon Chip mounted in a chassis – not floating around on your bench! Assuming the board is correctly installed, apply power and use your multi­meter to measure the three rails at the supply outputs (CON2 & CON3). If all is well, the +15V, -15V and +5V rails should all be within ±5% of the rated values. Now measure between pins 10 & 12 and then pins 10 & 13 of IC1’s socket on the control module. You should get readings just below the ±15V levels measured earlier. Finally, check between pins 5 & 4; again, the reading should be just below the earlier +5V measurement. Now switch off and allow about 30 seconds for the 1000mF filter capacitors to discharge. You can then insert IC1 & IC2 in their sockets, making sure that the notched (pin 1) ends line up with notches in the sockets! Before moving on, you must now program the microcontroller (IC2) if it’s blank – see the “Microcontroller Programming” panel. Initial setup Once construction and testing are complete, a simple setup procedure Table 2: jumper JP3 should be installed in the 1-2 position. must be followed to prepare the module for use. Before beginning, make sure that you’ve set up your remote control as per the information presented last month in the “Universal Infrared Remote Controls” panel. First, check that the power is switched off, then install jumper shunts on JP1 & JP2 (see Table 1) and JP3 pins 1-2 (Table 2). A jumper must also be installed on CON8 pins 1-3 (see Fig.7 and photos) at all times except when the microcontroller is being programmed. Note that if this jumper is missing at power up, the display will flash an error code of “90”. Now apply power while observing the “Ack” LED. It should flash five times to indicate that the unit is in set-up mode. The 7-segment display should be blank, except for the the “mute” indicator continuously flashing. Next, point your remote at the onboard infrared receiver (IC3) and press the numbers “1” or “2” twice. It’s significant which of these numbers is chosen. A “1” enables display blanking, meaning that the display will go blank eight seconds after each volume or balance adjustment. Conversely, “2” disables this feature, causing the display to be always on. On the second press, the “Ack” LED should flash five times again, indicating that the code was received and the chosen equipment address (TV, SAT, AUX, etc) successfully saved. You should now power down the unit and remove the setup jumper (JP1) only. This procedure can be repeated in the future should you wish to change the equipment address or display blanking option. In use As mentioned elsewhere in this article, volume span is effectively 127dB (-95.5dB to +31.5dB). As the PGA2310 supports 0.5dB gain steps, there are 255 steps from minimum to maximum volume. To fit this on a 2-digit readout and make it more intelligible, the level is scaled down to a 0-85 range by dividing it by three. The result is accurate to 1.5dB, so you’ll need to adjust the volume/balance by three points before you see a change in the readout. Note that “64” corresponds to 0dB (unity) gain – values below this attenuate the input signal, whereas those above it amplify. To increase or decrease the volume, siliconchip.com.au hit the “Vol Up” or “Vol Down” buttons on your remote, or turn the rotary encoder. With jumper JP2 installed, each press (or click of the encoder) moves the volume by just 0.5dB. If the remote’s button is held down so that it automatically repeats, the adjustment steps jump to 1.5dB after one second. Some audio systems may not require the fine 0.5dB adjustment steps. To increase the steps to 1.5dB for every button press or click, remove jumper JP2. In this case, holding down the remote’s buttons makes no difference to the step size, which always remain at 1.5dB. To adjust the balance between the left and right channels, use the “Ch Up” and “Ch Down” buttons on your remote instead. Alternatively, press the optional front-panel “Balance” button and use the rotary encoder. Each press or click adjusts the level by 0.5dB, regardless of the state of JP2. However, holding down the remote’s button for more than one second will case a temporary shift to 1.5dB adjustment steps. When in balance adjustment mode, the left inverted decimal point flashes Power Supplies (see Fig.15). Two dashes on the LED displays indicate that the balance is centred. Hitting the “Ch Down” button moves the sound stage left. On the first two presses, a single dash is shown in the left digit position, indicating the direction of “movement”. Likewise, one or two presses of the “Ch Up” button from the centred position results in a single dash in the right digit position. Subsequent presses display a num­ ber indicating the relative attenuation level of the opposing channel. For example, if the current volume level is set to 50 and the balance is favouring the left side and reads 5, the actual levels are: left = 50, right = 45. After four seconds of inactivity, the unit automatically reverts to volume adjustment mode. To bypass the foursecond delay and immediately exit balance mode, use the volume up/ down buttons on your remote or press the “Balance” button again. Both channels are simultaneously adjusted when the volume is increased or decreased, maintaining the balance separation. Note that when either channel reaches the maximum volume setting (ie, 85), further commands to Oscilloscopes RF Generators Fig.16: the mains earth lead must be securely attached to the base of the metal chassis. Here’s how to assemble a suitable earthing point for attaching two spade lugs. The two nuts lock the assembly in place. increase the volume are ignored. When one channel reaches the minimum volume position (0), further commands will continue to decrease the volume in the other channel until both are at minimum, if they are not identical. Increasing the volume from this minimum position restores the original balance separation. Muting Muting is achieved by hitting the Frequency Counters Spectrum Analysers HAMEG Instruments have always been recognised for the consistent quality and nocompromise value of German engineering. And now the news is even better! With more new products, an attractive educational discount scheme and lower prices for 2007 you owe it to yourself to find out more. Call us please on 1-300-853-407 Test Equipment: Sales, Service and Calibration siliconchip.com.au 1-300-853-407 www.triosmartcal.com.au March 2007  37 Microcontroller Programming Fig.18: the parallel port programmer uses PonyProg, which has an entirely different fuse configuration menu. Again, copy this example and hit the “Write” button. Fig.17: here’s how to set the fuse bits in AVR Prog, as used with the AVR ISP Serial Programmer. Once you’ve set all of the options exactly as shown, click on the “Write” button. I F YOU’RE BUILDING this project from a kit, then the microcontroller (IC1) will have been programmed and you can ignore the following information. Alternatively, if you’ve sourced all the components separately, then you’ll need to program the microcontroller yourself. A 10-way header (CON8) has been included on the PC board for connection to an “in-system” type programmer. Temporarily remove the jumper between pins 1 & 3 of CON8 to allow connection of the programming cable. Also, make sure that there’s a jumper between pins 1 & 2 of JP3. We described a suitable low-cost programmer in the October 2001 “Mute” or “12” buttons, depending on your model of remote. Hitting the mute button a second time immediately restores the original volume level, while pressing the “Vol Up” button restores the volume level and simultaneously increases it by one step. Note that pressing “Vol Down” while muted does decrease the volume level shown on the display but it doesn’t turn the muting off. This allows you to wind down the volume 38  Silicon Chip edition of SILICON CHIP. Kits for the programmer are currently available from Altronics (Cat. K-2885), on the web at www.altronics.com.au. Note that if you are using this particular programmer, the “Atmel AVR ISP” software described in the instructions is no longer available. A suitable alternative, named “PonyProg”, is available free from www.lancos. com. Set up PonyProg for the “AVR ISP (STK200/300)” parallel port interface as described in the included documentation for compatibility with the programmer. Some readers may also be familiar with the more recent “AVR ISP Serial Programmer”, described in the October 2002 edition. This newer programmer will do the same job but connects to your PC via a serial (rather than parallel) port. Kits for this programmer are available from Jaycar Electronics (Cat. KC-5340) – see www.jaycar.com.au Note that as published, the AVR ISP Serial Programmer cannot pro- to a respectable level first – perhaps when you’ve been caught out with the wick wound up far too high! Muting is indicated by the flashing of the second inverted decimal point (Fig.15, top left), which will continue to flash even during display blanking (when enabled). Multi-channel upgrade Finally, we’ve reserved buttons 1-6 and the optional “Channel” front- gram the ATMega8515 – the code in the programmer’s on-board micro must first be updated. An update is available from the SILICON CHIP website. If you’ve purchased your programmer as a kit, this update will already have been performed. Once you have a suitable programmer, together with the necessary cables and Windows software to drive it, all you need to complete the job is a copy of the microcontroller program for the Remote Volume Control & Preamplifier module. This can be downloaded from our website in a file named “DAVOL.ZIP”. This archive contains the file “DAVOL.HEX”, which needs to be programmed into the micro’s program (FLASH) memory. Just follow the instructions provided with the programmer and software to complete the task. Finally, the various fuse bits in the ATmega8515 must be correctly programmed, as depicted in Figs.17 & 18. If you miss this step, your module may behave erratically! panel switch for a possible future multi-channel upgrade. This would allow up to five simpler slave modules to be daisy-chained off CON8, all under your command via remote control! Pressing any of these buttons causes “C1” (meaning “Channel 1”) to appear on the display – but has no other function at present (Fig.15, top right). That’s it – your new Remote Volume Control is ready for use. Sit back and SC enjoy the music. siliconchip.com.au