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Does your amplifier have a remote volume control? It doesn’t? How can you bear it? It must be tough! Add this remote volume control to your stereo amplifier and life will never be the same again. By JOHN CLARKE L ET’S FACE IT, everything has remote control today and if your stereo amplifier doesn’t at least have a remote volume control, life must be really tough. Fortunately, we have the solution. We’ve slaved away to produce this infrared volume 28  Silicon Chip control and it can be added to most stereo amplifiers, provided you can find space behind the front panel for the motorised stereo potentiometer. When installed, the motorised potentiometer can be used in the normal way; just grab the knob and wind it up to set the volume. Or, by pushing the “UP” button on the handheld remote, it will be rotate by itself (as if by magic) and you can set the volume from your couch. Of course, you may now put on another 15kg of weight because you no longer have to get up to change the volume but that is a small price to pay, isn’t it? We think so anyway. Adding remote control to a stereo amplifier involves re­placing the original dual-gang potentiometer with a motorised version and installing a small controller PC board inside the amplifier as well. It needs a 9-15V DC supply which should be available within the amplifier. You can control www.siliconchip.com.au Fig.1: IRD1 picks up infrared signals from the remote control and feeds the demodulated data to the PIC microcontroller (IC1). IC1 in turn controls the motorised potentiometer via transistors Q1-Q4. it using a stan­ dard preprogrammed remote control. Using the remote Hey, we know you don’t need lessons in pushing buttons but humour us This slimline unit from Altronics (Cat. A-1013) can be used but lacks a mute button. www.siliconchip.com.au for a moment. After all, having slaved to produce this project, we need some gratification in telling the story. OK, when using the remote control, the standard volume up and down pushbuttons cause the motorised potentiometer to rotate clockwise or anticlockwise, as you would expect. If you keep pressing the up or down button, the motor can only drive the potentiometer so far and then an internal clutch slips so that no damage is done. The overall time taken for the pot shaft to rotate clockwise from min­imum to maximum is nine seconds and it takes the same time in the opposite direction. However, just pressing the up or down button is rather coarse and may not provide sufficiently precise setting of the volume. Consequently, we have provided a more precise method using the “channel up” and “channel down” buttons on the remote unit. Each time you press one of these buttons, the volume knob moves by about 1° of rotation. Alternatively, holding one of the buttons down will cause the volume knob to rotate from minimum to maximum in 28 seconds. Muting as well A feature of this unit is volume muting, something that many commercial amplifiers don’t have. Here it is done automatically using the Mute pushbutton on the remote. Push the Mute button once and the volume knob rotates fully anticlockwise. During this time the Mute LED flashes and then remains on after the volume knob has reached its minimum setting. June 2002  29 Parts List 1 PC board, code 15106021, 74 x 57mm 1 Alpha dual-ganged 20kΩ (or 50kΩ) log motorised pot 1 DIP 18-pin IC socket (for IC1) 1 2-way PC-mount screw terminal block (5.08mm pin spacing) 1 4MHz crystal (X1) 1 2-way pin header (2.45mm spacing) 1 2-way header plug (2.54mm spacing) 4 M3 tapped x 10mm Nylon standoffs 8 M3 x 6mm screws 1 300mm length of hookup wire 1 10kΩ (code 103) horizontal trimpot (VR1) Semiconductors 1 PIC16F84 programmed with “motorpot.hex” (IC1) 1 LM393 dual comparator (IC2) 1 infrared decoder (IRD1) 1 7805 5V regulator (REG1) 3 BC328 PNP transistors (Q1,Q3,Q5) 2 BC338 NPN transistors (Q2,Q4) 2 red LEDs (LED1,LED2) Capacitors 1 100µF 25VW PC electrolytic 1 100µF 16VW PC electrolytic 2 10µF 16VW PC electrolytic 3 0.1µF MKT polyester 1 .01µF MKT polyester or ceramic 2 22pF ceramic Resistors (0.25W, 1%) 1 68kΩ 2 10kΩ 2 22kΩ 6 1kΩ 1 18kΩ 2 10Ω WHERE TO GET THE SOURCE CODE For those interested in pro­gramm­ ing their own microcon­troller, the source code (motorpot.asm) can be downloaded from our website: www.siliconchip.com.au Pressing the Mute button again will return the volume to its previous setting; well, within 1.5° of rotation. How does it do that? The drive controller actually measures the time the volume knob takes to reach the minimum setting. Then, when the Mute button is pressed again to restore the volume, power is applied to the motor 30  Silicon Chip drive for the same amount of time. During the muting and return, the process can be stopped by pressing the Mute button again or using one of the volume buttons. incoming serial data from IRD1. If the de­tected code is correct, the motorised potentiometer will be driven according to the pushbutton command sent by the remote control. No noise Motor drive The control circuitry is designed so that it doesn’t introduce any noise into any sensitive sections of the amplifier into which it is installed. Normally, when there is no IR signal being transmitted by the remote, the circuit is quiescent and produces no noise. As soon as it receives an infrared signal it responds by driving the motorised potentiometer and then shuts down after about 1.2 seconds if it does not receive any further infrared signals. The motor too is enclosed in a Mumetal shield which reduces any electrical hash caused by the sparking of the brushes against the commutator. A .01µF capacitor across the motor terminals prevents the hash signals being sent along the connection wires. The motorised potentiometer is driven by four transistors (Q1-Q4) which are driven via the RB2, RB3, RB4 and RB5 outputs of IC1 via 1kΩ resistors. When the motor is off, the RB2-RB5 outputs are all set high. The high outputs at RB4 and RB5 switch off transistors Q1 and Q3 while the high outputs at RB2 and RB3 drive transistors Q2 and Q4 so that they are turned on. Both terminals of the motor are thus held low. The emitters of Q2 and Q4 connect to ground via a 10Ω resistor. To drive the potentiometer clockwise, Q2 is switched off via a low level on RB3 and transistor Q1 is switched on via a low on RB4. Thus the lefthand terminal of the motor is taken to +5V via Q1 and the righthand terminal of the motor is low via Q4. To drive the potentiometer anticlockwise, Q1 & Q4 are switched off and Q2 & Q3 are switched on. Thus the righthand motor termi­nal is pulled to +5V via Q3 and the lefthand terminal is low via Q2. The voltage across the motor is dependent on the voltage drop across the 10Ω emitter resistor of Q2 & Q4. Typically, the motor draws 40mA when driving the potentiometer and over 50mA when the clutch is slipping. Thus, the motor voltage is around 4.54.6V due to the 0.4-0.5V drop across the 10Ω resistor. Rated motor voltage is 4.5V. Comparator IC2 monitors the voltage across the 10Ω resistor via a filter comprising an 18kΩ resistor and 0.1µF capacitor. This removes the commutator hash so that a smooth voltage is applied to the inverting input at pin 6. VR1 is adjusted so that the voltage at the non-inverting input at pin 5 is about +0.45V. When the motor is running normally, the 40mA drawn by the motor produces 0.4V across the 10Ω resistor. Since this voltage is lower than the set voltage at pin 5, the comparator output at pin 7 is high. When the potentiometer reaches the end of its travel, the extra load from the slipping clutch raises the voltage across the 10Ω resistor to above the voltage set at pin 5. The comparator output at pin 7 then Circuit details The complete circuit for this Remote-controlled Motorised Potentiometer is based on a PIC16F84 microcontroller. It monitors the demodulated infrared signal from the detector IRD1. It decodes the signal and drives the motor according to the code sent by the handheld remote. IRD1 only has three leads but it is not a simple device; it is a complete infrared detector and processor. It picks up the infrared signal which comprises a series of 38kHz pulses. The signal is amplified to a constant signal level, fed to a 38kHz bandpass filter and then demodulated to produce a serial data burst which is fed to the RB0 input of IC1 at pin 6. IC1 is programmed to recognise the RC5 Code. This is a standard infrared remote control code used by Philips and asso­ciated manufacturers. The remote volume control can be operated on one of four codes within the RC5 Code. These are TV1, CD, SAT1 and SAT2. These are selected using links LK1 and LK2 at the RB7 and RB6 inputs of IC1. Both these inputs are pulled high using internal resistors in IC1 but can be pulled low with links LK1 and LK2. IC1 monitors the level of these inputs and uses the selected code to compare with the www.siliconchip.com.au Fig.2: the top trace shows the motor drive voltage which is about 5V when the motor is running. The lower trace is the voltage across the 10Ω current sensing resistor. This is less than 50mV while the motor is turning the pot shaft but rises above 120mV when the endstop is reached. This is detected by IC2 and IC1 switches off the motor during muting. goes low. This is detected by the RA0 input of IC1 but this only happens during the Muting operation, so that the motor can be stopped immediately that pin 7 of IC2 goes low. At other times, when the volume is being set by the Up or Down buttons, the RA0 input is not being monitored, so the clutch will begin to slip if the potentiometer is driven past its clock­ wise or anticlockwise limits. The Acknowledge and Mute LEDs are lit when their respective RB1 and RA1 outputs are pulled high via their 1kΩ resistors. The Acknowledge LED lights when the RB0 input receives an infrared signal while the Mute LED flashes during the Mute operation and then stays lit while muted. Pins 15 and 16 of IC1 are the oscillator inputs for the 4MHz crystal. The oscillator runs when first powered up for about 1.5 seconds and also when- Fig.3: the top trace here shows the output from the infrared receiver (IRD1) when the Mute signal is being transmitted. The middle trace is the tracer signal as seen at pin 1 of IC1. IC1 monitors IRD1’s voltage when the trace level is high and the resulting decoded IR signal is shown on the lower trace, as measured on pin 2 of IC1. ever an infrared signal is received at RB0 and then for 1.5 seconds after the last receipt of sign­al. Oscillator shutdown ensures that there is no radiation of noise into sensitive audio circuitry when the volume control is not being altered. Transistor Q5 provides a reset for IC1 should the supply at pin 14 drop below a certain value. It works as follows. The emitter of Q5 is supplied with close to +5V via the 10Ω resistor. Q2’s base voltage is held at 0.6V below the emitter via the 10kΩ and 68kΩ resistors connecting across the 5V supply. With Q5 switched on, the collector is pulled high and so pin 4 is also held high at around +5V. IC1 can then operate normally. Should the supply drop below +4.68V, Q5 will turn off and the 22kΩ collector resistor will pull pin 4 of IC1 low, placing IC1 in its reset condition. The same process happens at power up. As the supply is switched on, pin 4 is held low via the 22kΩ resistor until the supply goes above 4.68V. Note that the RA4 input is tied to pin 4 via link LK3. This enables the “mute return” feature. Connecting the RA4 input to ground by cutting the track to pin 4 and soldering a bridge to ground will indicate to IC1 that the “mute return” feature is disabled. RB6 and RB7 are for different in- MAIN FEATURES • • • Infrared remote control • Muting facility (automatic volume down) A Brief Primer On RC5 Code • Mute return (automatic volume up) This standard code comprises 14 bits, with the first two as high level start bits. The third bit is the toggle bit which can be either high or low and toggles between a high or a low each time a key is pressed on the remote control. The toggle bit does not change if one of the keys is con­tinuously pressed. It is used to inform the decoder whether a key was pressed continuously or pressed more than once. The following bits are five address bits and six keycode or command bits. The address bits define what item of equipment is being controlled, while the command bits determine what function is to be carried out via remote control. Finally, the bits are separated by 1.778ms and the code repeats every 113.778ms. • Uses commercial preprogrammed remotes • Original knob volume control movement retained • • • • Optional mute return disable www.siliconchip.com.au Volume Up and Down Special precision volume adjustment Acknowledge indicator Mute indication No switching noise injected into amplifier June 2002  31 potentiometer requires considerable room (depth). In some cases, you might be able to make more room by locating parts onto the underside of existing PC boards. In addition, there must be room for the additional PC board inside your amplifier and a DC supply of between +9 and +15V which can deliver up to 70mA when required. Standby current for the circuit is around 15mA rising to 60-70mA when the motor is running. You can begin assembly by checking the PC board for any shorts between tracks or hairline breaks. Also, check the hole sizes for each component. In particular, the PC mounting screw terminals need to be 1.5mm diameter, while the 2-way pin header for the motor connections requires 1mm diameter holes. Corner mounting holes should be 3mm in diameter. Install the two wire links and the resistors first, using the colour code table as a guide to selecting values. Insert and solder IC2 and the socket for IC1, taking care with orientation. Capacitors and transistors can be mounted next. Be sure the electrolytic capacitors are installed with the correct polarity and take care with the transistors as there are two different types. Q2 and Q4 are BC338s. Next, install VR1, REG1, the screw terminals and the 2-way pin header. The LEDs and IRD1 are located on the edge of the PC board so that they can be inserted into suitable holes in the front of the amplifier. If there is insufficient room for this PC board to be placed near the front panel, you can use a satellite board which carries just IRD1 (the infrared receiver) and two LEDs. We will have more details on this next month, when we describe how this project is in­ stalled in the Ultra-LD 100W Stereo Amplifier. Next, solder the .01µF ceramic CHOOSING A REMOTE CONTROL This Remote Volume Control should work with just about any preprogramm­ ed IR remote transmitter that can control a Philips TV set, a satellite receiver, a VCR or a CD play­ er. It’s just a matter of programming The G-1223 IR it by following the remote is availinstructions (see able from DSE. text). Suitable IR remote controls include: Altronics Cat. A-1013 and Cat A-1009; Dick Smith Cat. G1223; and Jaycar Cat. AR-1073 (Select 1) and Cat. AR-1710 (Big Shot 3). If you already have a multi-function remote control (ie, one that can control a TV set, a VCR and a satellite receiver), then you don’t need to buy frared coding options. The default selection is when both RB6 and RB7 are held high via their internal pullup resistors. This selects the TV1 infrared remote control code which will be suitable for most applications. However, this code may also operate your TV and so we have pro­vided options to select another code to prevent this from happen­ing. Table 3 shows the linking options to select the CD, SAT1 or SAT2 codes. As an example, tying LK2 to ground Table 1: Capacitor Codes     Value IEC Code EIA Code 0.1µF   100n   104 .01µF 10n   103 22pF  22p   22 The Altronics Cat. A-1013 (top) and Cat. A-1009 IR remotes are both suitable but note that the A-1013 has no mute button. another remote. Just use the satellite function or some other function (eg, VCR or CD) for the Remote Volume Control. via a solder bridge will set the code to CD. Power requirement for the circuit is a 9-15V DC supply which can deliver up to 70mA. REG1 sets the supply to +5V, suit­able for IC1, IC2 and IRD1. Capacitors at the input and output of REG1 provide filtering of the supply, while the 10µF capacitor across IRD1 prevents this device from feeding hash back into the 5V rail. Construction The Remote-Controlled Motorised Potentiometer is assembled onto a PC board coded 15106021 which measures 74 x 57mm. Important note: before you even purchase the kit for this project, you need to ensure that there is sufficient space behind the existing volume control of your amplifier. The motorised Table 2: Resistor Colour Codes  No.   1   2   1   2   6   2 32  Silicon Chip Value 68kΩ 22kΩ 18kΩ 10kΩ 1kΩ 10Ω 4-Band Code (1%) blue grey orange brown red red orange brown brown grey orange brown brown black orange brown brown black red brown brown black black brown 5-Band Code (1%) blue grey black red brown red red black red brown brown grey black red brown brown black black red brown brown black black brown brown brown black black gold brown www.siliconchip.com.au Fig.4 (left): install the parts on the PC board as shown here but don’t install IC1 (the PIC microcontroller) until the power supply has been tested. Note particularly that transistors Q1 & Q3 are BC328s, while Q2 & Q4 are BC338s – don’t get them mixed up! The numbers in red correspond to connections to the satellite board to be described next month. capacitor and connection wires to the motor terminals of the motorised potentiometer. Crimp the other ends of the wires to the 2-way pin header plug pins and insert the pins into the header plug shell. Then attach the motor cable to the motor pin header terminals on the PC board. Testing Before installing IC1 into its socket, connect power to the screw terminals on the PC board using a DC supply of 9-15V. Now measure the voltage between pins 5 & 14 of IC1’s socket – you should get a reading between 4.8V and 5.2V. If this is correct, switch off the power and insert IC1 into its socket. Further testing requires a universal remote control. These range from single TV remote controls with limited functions to elaborate models capable of operating many different types of equipment. Note that simple TV remote controls will only operate this project with the code selected for TV. If you have a Philips TV set located in the same area as your amplifier, the remote con­trol will probably operate the TV as well. In this case, you will need to select a different code which means that a multi-item remote control will have to be used. Examples of TV-only remote controls are the Jaycar AR-1703 and the www.siliconchip.com.au Dick Smith G1223. Multi-item remote controls include the Altronics A-1009 and the Jaycar AR-1710. Programming the remote Program your remote control initially for a Philips brand TV by following the instructions supplied with the unit. In most cases, programming means that the set button is pressed along with the item which is to be operated. In other words, press SET and TV together and enter a number quoted for a Philips TV set. In this case, the Jaycar AR-1710 and Altronics A-1009 and A-1013 remote controls use the number 191; the DSE G-1223 uses 11322; and the Jaycar AR-1703 uses 11414. If you are using a different remote control, select a number for a Philips TV set. If it does not operate the motorised potentiometer, try another number for a Philips TV. Now rotate VR1 fully clockwise and check the motor turns the potenti­ ometer clockwise when the volume up and channel up buttons are pressed. That done, check that the potenti­ ometer runs anticlockwise with the volume down and channel down buttons. If the potentiometer turns in the wrong direction, reverse the leads connected to the motor. Check that the Acknowledge LED lights each time you press a button on the remote. Now press the Mute button and wait until the motor winds the pot fully anticlockwise. Now adjust VR1 clockwise until the motor stops. Press mute again or the volume up button to turn the potentiometer clockwise. Now press mute again and check that the motor stops when the potentiometer reaches its end of travel. Note that there is a timeout of 13 seconds which will stop the motor after the mute has been activated. So do not take too long in adjusting VR1 or the timeout will stop the motor rather than the adjustment of VR1. Note also that with a new motorised potentiometer, the clutch will require a little wearing in to spread the lubricant in the slipping The Jaycar AR-1073 (top) and AR1710 IR remotes are also suitable. June 2002  33 A-1009/A-1013 and Jaycar AR-1710 remotes are 651 for CD, 424 for SAT1 and 425 for SAT2. Table 3: Link Options Installation Fig.5: this is the full-size etching pattern for the PC board. sections evenly. This can be done simply by turning the pot shaft by hand a few times before use. Readjust VR1 for best results. When the motor stops reliably at the anticlockwise end stop, press the mute after it reaches its fully anticlockwise position. This should cause the potentiometer to accurately return to its previous position. If the mute return feature is not required, cut the thinned track connection between pins 3 & 4 of IC1 and join pin 3 to the ground with a bridge of solder. (The ground is the heavy copper track that runs down the centre of IC1). Changing the codes for the infrared transmission is done by soldering bridge connections between pin 13 of IC1 and ground and pin 14 of IC1 and ground, as detailed in Table 3. For example, connect pin 13 (LK1) to ground to select SAT 1. The relevant codes for the Altronics As noted, the motorised potenti­ ometer replaces the original volume control in the amplifier. There needs to be sufficient room behind the potentiometer for the motor and gearbox section to fit without fouling any part of the amplifier. You may need to shorten the shaft of the potentiometer to suit the amplifier’s volume knob. Or possibly the knob may need changing or modifying to suit the shaft. After installing the potentiometer, check that the metal body of the motorised section is connected to chassis; use a multimeter set to the low “ohms” range. The motorised potentiometer is connected to the amplifier with the same connections as the original potentiometer. Typical­ ly the anticlockwise end of the potentiometer connects to ground or to the common point of the amplifier, the clockwise or top end of the potentiometer connects to the preamplifier output via a coupling capacitor and the wiper connects to the power amplifier. Note that the coupling capacitor that connects to the top end of the potentiometer may need to be changed if the value of the motorised potentiome­ter is different to the original. In practice, though, if the new potentiometer is only twice or half its original value, there should be no need to change the capacitor. For larger variations in potentio­ meter value, it may be necessary to change the coupling capacitor value. This is because the low frequency response of the amplifier may be al- This table shows how to change the infrared code function using links LK1 & LK2 (see text) tered. The new value of capacitance is calculated by scaling the original value by the ratio of the difference between the original poten­tiometer value and the new pot value. So if the new pot value is smaller than the original, make the capacitor value larger by the same amount. If the new pot value is larger than the original then no changes are necessary. Find a position for the remote control receiver PC board to fit into the amplifier case. The location should take into ac­count the fact that IRD1 and the LEDs need to protrude through small holes in the amplifier front panel. Satellite board As mentioned before, if there is insufficient room for the PC board close to the front panel, you can use the satellite PC board which carries the infrared receiver (IRD1) and LEDs only. We’ll describe the satellite board next month. Finally, you need to find a suitable DC power supply connection for the infrared receiver PC board. The voltage required is 9-15V DC at up to 70mA. Be sure to connect the correct polarity to the power terminals of the receiver SC PC board. MINI SUPER DRILL KIT IN HANDY CARRY CASE. SUPPLIED WITH DRILLBITS AND GRINDING ACCESSORIES $61.60 GST INC. 34  Silicon Chip www.siliconchip.com.au