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Remote volume control for hifi systems; Pt.2 Remote volume controls are now common in commercial rack hifi systems but this design is far superior in its dynamic range, tracking and signal-to-noise ratio. This month, we describe the construction of the unit & show you to connect it to your hifi system. mitter is housed in a small plastic case which has a front panel label measuring 73 x 63mm. A PC board coded 01305933 and measuring 62 x 59mm clips inside this case. Five small plastic chrome buttons protrude through the front panel and are used to press down onto click action switches mounted on the PC board. Before starting construction, check all three PC boards for breaks in the copper tracks or shorts between tracks. Any defects should be repaired before proceeding further. Check that all holes have been correctly drilled also. links are straight to avoid shorts and note that the 27Ω 5W resistor must be mounted about 1mm above the board because it runs rather warm. The ICs can now be installed, taking care with the orienta­ tion of each device. We used a high quality machined pin socket for IC1 but we recommend you don’t use sockets for the remaining ICs as they will tend to prejudice the audio performance. Do not insert the microprocessor into its socket at this stage. Next, install the diodes, regulators and capacitors, taking care to ensure that all polarised components are correctly oriented. Note that the 4700µF and 330µF capacitors are mounted on their sides so that they don’t touch the lid of the case. Each 3-terminal regulator is bolted to the board with a screw and nut, while REG1 is also mounted on a small heatsink. The mating faces of the regulator and heatsink should be smear­ ed with heatsink compound during assembly. Finally mount the relay, switch S2, the ceramic resonator and the crystal. Main board assembly Display board Begin assembly of the main PC board (01305931) by install­ ing the PC stakes, wire links and resistors – see Fig.6. Make sure that all the wire You should follow the assembly details for the display board (01305932) carefully, since the method is unusual. Begin by installing the By JOHN CLARKE Building the Remote Volume Control involves the assembly of three PC boards, some metalwork and the internal wiring. To keep this article reasonably brief, we shall assume that you are building the project up from a kit which has a pre-punched case and screen printed panels. The Remote Volume Control receiver is housed in a 1-unit high rack mounting case. It uses two PC boards: a main board coded 01305931 and measuring 283 x 161mm; and a display board coded 01305932 and measuring 283 x 39mm. The screen printed front panel artwork measures 480 x 44mm, while the rear panel artwork measures 180 x 34mm. The front panel also incorporates a red Perspex window measuring 150 x 20mm, for the LED displays. The handheld remote control trans64  Silicon Chip Fig.6: install the parts on the main & display boards as shown here & use a socket for IC1. Note the two wire links (dotted) that run under the LED displays. IC1 is installed after the initial power supply checks have been made. June 1993  65 A 100pF 0.1 LED1 K 100pF X2 10uF .015 4.7k 27  5W K S5 6.8uF 47uF G 0.15 A 1 10uF 0.22 .0047 S3 10uF 22uF S4 D9 D10 270  10k 10k 0.1 REG1 7805 IC11 MV601 0.1 IC10 SL486 A 39pF X1 IC2 4511 1uF D11 D8 D7 D6 39pF 10k G IRD1 K 270  270  270  270  270  1 10k DISP1 270  270  10uF 1 IC3 4511 4.7M DISP2 1 270  DISP3 1 A 0.1 1 1 220pF 220pF DISP4 IC5 UCN2003 IC7 AD7112CN IC4 4511 IC1 MC68HC705C8P 270  4700uF 25VW 270  HEATSINK 47  0.1 270  270  270  270  270  REG2 7815 270  270  270  270  270  270  270  10uF 0.1 270  10uF 270  REG3 7915 270  10uF 270  330uF 25VW 270  D5 270W 470uF 1 1 0.1 1 0.1 IC9 OP27 0.1 0.1 IC8 OP27 IC6 ULN2003 270W 120  270W 120  270W D1-D4 K S2 RELAY 1 D12 10k 10k LED2 Fig.7 (left): this is the parts layout for the transmitter PC board. Be sure to orient the pushbutton switches exactly as shown & note that S1 & S4 face in the opposite direction to S3, S2 & S5. The two LEDs are mounted at full lead length – see text. LED1 K A K A Q1 2. 2  220uF 100pF 9V BATTERY 100pF 10  X1 1 LK1 LK2 S4 IC1 MV500 S5 10k S2 S3 Fig.8: the transmitter is encoded to match the receiver by installing links LK1 & LK2 on the copper side of the PC board. If necessary, the coding can be changed by installing different link options, as described in the text. S1 wire links on the board, then install three PC stakes from the copper side of the board at the A, K and GND locations adjacent to infrared diode IRD1. The three pushbutton switches (S3-S5) and the three 7-seg­ment LED displays mount onto pins to raise the level of these components by about 7mm. This is necessary so that the switches ultimately protrude through the front panel of the case, with the LED readouts just behind the Perspex window. We used machine pins from an IC socket for this job. They can be removed by pushing each one through from the underside of the socket using a pair of small pliers. Be sure to orient the switches correctly (ie, flat side of the switch to the left of the PC board, as shown in Fig.6). The infrared diode (IRD1) is mount­ ed with its leads at full length (don’t cut them short!) and bent at right angles so that its front face sits vertically. LED1 should be installed with just its anode lead soldered at present so that its height can be adjusted later – don’t cut its leads. Orient the 10-LED array (DISP4) with the anode leads (longer leads) to the left and set the array at the same height as the 7-segment displays. Mating the two boards The main board is butted to the back of the display board at right angles. It must be arranged so that its underside is 5mm above the bottom edge of the display board. How do you do this? First, support the main board upside down on a flat surface. The easiest way to do this is to fit long screws to the four mounting points on the board so that they become the supports. This done, stand the display board on its topside edge and butt it to the main board. Adjust their positions so that the display board has its edge 5mm above the copper side of the main board. When everything is correct, tack solder the two boards together at either end. Finally, check that the two boards are butted correctly and are at right angles before soldering the remaining tracks. Transmitter board The transmitter board should first be tested for fit into the base of the handheld case. Check that the clips hold the board correctly and that the alignment pin on the base of the case CAPACITOR CODES ❏ ❏ ❏ ❏ ❏ ❏ ❏ ❏ ❏ Value IEC code EIA code 0.22µF 220n 224 0.15µF 150n 154 0.1µF 100n 104 0.015µF   15n 153 .0047µF   4n7 472 220pF 220p 221 100pF 100p 101 39pF   39p   39 RESISTOR COLOUR CODES ❏ No. ❏   1 ❏   7 ❏   1 ❏ 32 ❏   1 ❏   1 ❏   1 66  Silicon Chip Value 4.7MΩ 10kΩ 4.7k 330Ω 47Ω 10Ω 2.2Ω 4-Band (1%) Code yellow violet green brown brown black orange brown yellow violet red brown orange orange brown brown yellow violet black brown brown black black brown red red gold brown 5-Band Code (1%) yellow violet black orange brown brown black black red brown yellow violet black brown brown orange orange black black brown yellow violet black gold brown brown black black gold brown red red black silver brown The two PC boards in the receiver are soldered together at right angles & mounted on the base of the chassis on 5mm spacers. Check that the three momentary-contact switches operate smoothly when the front panel is bolted into position & adjust them if necessary. passes through the hole in the centre of the PC board. If the PC board is too long, it will need to be filed down to size. Once the PC board clips properly into the case, snip off the top of the plastic alignment pin with a pair of sidecutters so that it is flush with the top of the PC board. This will allow the IC to sit over the alignment pin. Begin the assembly by installing the IC, the link and the resistors – see Fig.7. This done, install PC stakes for the battery connections, then install the two 100pF capacitors and the ceramic resonator. The 220µF electrolytic capacitor must be mounted on its side as shown in Fig.7. Each pushbutton switch S1-S5 should be mounted with its flat side oriented as shown on the layout diagram. Transistor Q1 is mounted with its leads bent at right angles and is bolted to the PC board using a screw and nut. The two LEDs are mounted without shortening their leads, so that they can sit on the plastic cup rests at the front of the case. Finally, you need to install links LK1 and LK2. These set the data rate of the transmitter to match the data rate set for IC11 in the receiver circuit. LK1 and LK2 tie pins 14 & 15 of IC1 high and are installed on the copper side of the PC board – see Fig.8 (note: this coding can be changed if necessary, as described later). When the assembly is completed, clip the board into the case and bend the LED leads so that they sit on the plastic cup rests. This done, pass the battery clip leads through from the battery compartment and connect them The transmitter switches are activated by chromed plastic buttons which pass through the front panel of the case. Each button is modified by gluing it to a second chrome button mounted side on. June 1993  67 the top. Finally, check that the buttons activate the switches properly. Receiver chassis The three pushbutton switches (S3-S5) and the 7-seg­ment LED displays are mounted on IC socket pins so that they sit about 7mm above the board surface. This is necessary so that the switches ultimately protrude through the front panel of the case, with the LED readouts just behind the Perspex window. Although optional, a black cardboard mask can be fitted to prevent light leakage around the LED displays. The viewing window for the 7-segment readouts is fitted with a plastic filter to improve display contrast. to the PC board, taking care to ensure correct polarity. Check that switch S3 clears the side of a plastic bush in the base of the case. If necessary, this bush can be shaved down with a sharp knife. As mentioned previously, the switches on the PC board are activated by chromed plastic buttons which pass through the front panel of the case. To prevent excessive play between the base of the chrome buttons and the top of the switches 68  Silicon Chip on the board, the base of each button is shimmed up with a second chrome button mounted side on. Use super­ glue to glue the buttons together (see photo) and file down the side lobes on the shim piece. The front panel label can now be affixed to the transmitter case and a sharp knife used to make the rectangular cutouts for the chrome buttons. This done, load the five chrome buttons through the back of the case lid, then clip the lower case assem­bly over Work can now begin on the receiver chassis. Assuming that the chassis holes are pre-drilled, you can secure the side and rear panels to the base­ plate but leave the front panel off at this stage. Next, mount the RCA sockets, switch S6, solder lug and fuseholder F1 on the rear panel and install the mains cable. The transformer, earth lug, terminal block and PC board assembly can then be mounted on the baseplate (mount the board assembly on 5mm spacers). The front panel can now be secured to the baseplate and the power switch installed. Check that the Mute, Down, Up and Tape Monitor switches operate smoothly in the front panel cutouts. If the click action switches foul the front panel they can be ad­justed by removing the panel and pushing the switches to one side. To simplify the wiring procedure, we have produced a sepa­rate diagram of the whole chassis – see Fig.9. Be sure to use 250VAC-rated cable for the wiring to the mains switch (S1), mains terminal block and the transformer primary. Insulating sleev­ ing (eg, heatshrink tubing) should be used to cover the bare terminals of the fuse and mains switch, to prevent accidental contact. Don’t forget to solder the .0047µF 250VAC capacitor across the mains switch. The green/yellow earth wire is connected to an earth lug terminal on the base of the chassis. Make sure that this terminal is properly connected to chassis by scraping away the paint or anodising from the surrounding area of the hole. Once this termi­nal is secured with a screw, nut and spring washer, measure the resistance between the chassis and earth terminal to ensure that it is indeed a good connection – the meter should read 0Ω. Similarly, the earth terminal at the ▲ Fig.9 (right): be sure to use mainsrated cable for all the mains wiring & sleeve all exposed wiring with heatshrink tubing to eliminate the possibility of electric shock. The remainder of the wiring (except to S6) is run using shielded cable. June 1993  69 The transmitter case was sprayed black to match the receiver chassis. Check that the acknowledge LED on the receiver comes on each time one of the buttons on the remote control is pressed. Now check the operation of the remote control. The ACK (acknowledge) LED on the receiver should light when one of the remote control switches is pressed. Check that the Up, Down and Mute switches operate the receiver displays correctly. Note that you can control the balance only when the receiver is unmuted. Note also that the balance display can show two LEDs lit at the same time. If the balance setting is 0dB, 3dB, 6dB or 9dB, only one LED will be lit but for in-between settings, such as 4.5dB or 7.5dB, two LEDs will be lit. Connecting it to your hifi rear of the chassis should make a 0Ω connection to the rear panel. Check also that the rear panel is electrically connected to the chassis by again measuring the resistance between them with your multimeter. If not, you may need to remove paint from around some of the screw holes for the various panels. The mains wiring should be neatly anchored with plastic cable ties. This not only makes it look tidy but also stops the wiring from coming adrift. All of the signal wiring is run using shielded cable. Use a short length of twin shielded cable for the wiring from the infrared detector (IRD1) on the display board to IC10 on the main board. Twin shielded cable is also used between the INPUT sockets and the TAPE OUT sockets. Use single shielded cable for the remaining audio wiring and use plastic ties to anchor the wires in place. Testing Before applying power to the unit, check your wiring care­fully. Note that the microprocessor, IC1, should not be installed just yet. Now apply power and check that the +5V supply rail is between +4.75 and +5.25V. If not, switch off the power and locate the problem before switching on again. Check that +15V is present at pin 7 of IC8 & IC9 and that -15V is present 70  Silicon Chip at pin 4 of IC8 & IC9. Check that +5V is present at pins 1, 3, 37 & 40 of IC1’s socket; at pins 3, 4, & 16 of ICs 2, 3 & 4; at pin 7 of IC7; at pins 4 & 7 of IC10; and at pins 5 & 16 of IC11. If everything is correct, switch off and install IC1. Make sure that IC1 is correctly oriented, then apply power. The LED display should show 48.0 and the balance LEDs should all be lit. If so, press the Mute control to check that all the balance LEDs except the 0dB LED extinguish. If everything is working correctly, pressing the Up and Down switches should alter the attenuation display in 1.5dB steps. Note that pressing the Up switch will decrease the atten­uation reading while pressing the Down switch will increase the attenuation reading. Where to buy the microprocessor The coded 68HC705C8P microprocessor will be available only from SILICON CHIP magazine and is priced at $45 including sales tax. For postage and packing to anywhere within Australia, please add $6.00. Payment may be made via cheque, postal money order or credit card authorisation (Bank­ card, Visa and Mastercard). When all checks are done, you are ready to connect the unit to your hifi system. If you have a separate preamplifier and power amplifier, the Remote Volume Control is connected between the two. If you have an integrated amplifier, the Remote Volume Control is wired into the Tape Monitor loop. The Remote Volume Control has its own tape monitor loop to replicate the loop on the amplifier. Switch on your hifi system and check that the volume and balance are adjustable via the handheld remote control. You will need to turn up the volume control on your integrated amplifier or preamplifier to the maximum to obtain the full volume range from the remote control. With the volume setting advanced and no signal present, check the noise level from your loudspeakers. It should be no more than the noise level from your system without the remote control in circuit. If you have a low level hum, try the “earth” or “float” settings of the rear panel switch (S6). This has been included to cope with systems which are earthed or double insu­lated. Finally, we should comment on the transmitter and receiver coding. We have presented only one coding option and we do not anticipate that it will be necessary to change it. However, if you do encounter interference from other IR remote controls, try changing the coding using different link options. For example, you could install either LK1 or LK2 (but not both) on the receiver board (see Fig.4) and change the transmitter coding to match (eg, if LK1 is installed in the receiver, install LK2 & LK3 on the SC transmitter (see Fig.5).