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Don't spend big bucks on batteries for your Sony Walkman ®. This simple voltage regulator will let you power it from a plugpack supply or from your car's cigarette lighter socket. The If you like listening to your personal player in the car or while relaxing in your favourite chair, then this project is a must. It's a very simple voltage regulator circuit that's designed to conserve the player's batteries for those times when you want to listen "on the move". We've christened the project The Eliminator because that's just what it does - when it's plugged in, it effectively eliminates (or bypasses) the player's internal battery. In use, The Eliminator is simply connected between a plugpack supply (or car battery) and the player's DC socket. Its job is to accept the +12V (nominal) from the 36 SILICON CHIP By MARQU E CROZMAN plugpack supply and regulate it to the DC voltage required to run the player. Because it only uses low-cost parts, the savings in batteries will very quickly pay for this project. It's also a snack to build and get going. In fact, we reckon that even a rank beginner could build this design. The circuit can also be easily customised to meet your requirements. Some personal players require two AA cells (3V), while others require three (4.5V) or even four (6V). For this reason, we've designed the project so that it can deliver either 3V, 4.5V, 6V or 9V. All you have to do is select one resistor value from a table. An important safety aspect of this project, particularly for beginners, is that no mains wiring is required. Instead, it's designed to run from a car battery or from a DC plugpack supply. You can use any DC plugpack supply with a rated output voltage of 9-12V. However, the project is not just confined to powering personal players from a DC supply. Because it was originally intended for use in a mainspowered project, the PC board also has provision for a four-diode bridge rectifier. By adding this bridge rectifier, the circuit can be powered from a 15VAC (or less) mains transformer. In this application, however, the 02 1N4004 ~.....__ _ _ _ _ _ _ _,-..,-•3V D3 1N4004 10 + 16VW - Fig.1: the circuit is based on an LM317 3-terminal adjustable regulator. The output voltage can be varied between 3V & 9V by choosing the value ofR2, as shown in Table 1. LED1 OVO---,.__ ___.,_ _ _ _ _ _ _ _ _ _...,.._OV THE ELIMINATOR TABLE 1 R2 Output 180 ohms 3V 330 ohms 4.5V 470 ohms 6V 750 ohms 9V four diodes in the original bridge rectifier have been replaced by a single diode (Dl) and a wire link. We don't need the bridge rectifier, since we are using a DC supply only. Circuit details Refer now to Fig.1 which shows the circuit details. As you can see, The Eliminator is based on an LM317 3-terminal positive voltage regulator. This device is capable of delivering up to 1.5A (with adequate heatsinking), has an output voltage range from 1.2-37V, and features internal thermal overload and short circuit protection, In short, it is virtually "blow-up" proof. Let's take a closer look at how it works. The+ 12Vrail from the plugpack (or car battery) is applied to the input of the LM317 regulator via reverse polarity protection diode Dl. In operation, this regulator is designed to provide 1.25V between its OUT and ADJ (adjust) terminals but note that the current flowing through the ADJ terminal is negligible. This makes the device extremely easy to use, since we require just two resistors to set the output voltage. Since the voltage between the OUT and ADJ terminals is fixed at 1.25V, it follows that the current through Rl and R2 is also fixed. This gives a simple formula for the output voltage, as follows: V001 = 1.25(1 + R2/Rl) In our circuit, Rl is fixed at 120Q while R2 is selected from Table 1 to give the required output voltage. In our case, we used a value of 180Q to obtain a 3V output. If you want a 4.5V, 6V or 9V output, then just select the appropriate resistor value from Table 1. Alternatively, you could replace R2 with a lkQ trimpot to make the output continuously variable over the 1.259V range. A lO0µF electrolytic capacitor is used to filter the incoming supply PARTS LIST 1 PC board, code SC04104921, 48 x 61mm 1 aluminium case 100 x 58 x 45mm (Jaycar Cat. HB-5100) 1 Dynamark front panel label, 55 x 190mm 4 68A x 10mm machine screws, nuts & lock washers 6 PC stakes 1 200mm length of medium~duty hook-up wire Semiconductors 3 1 N4004 diodes (D1 -D3) 1 LM317 voltage regulator 1 5mm LED (LED 1) Capacitors 1 100µF 25VW PC electrolytic 2 10µF 25VW PC electrolytic Resistors (0.5W, 1%) 1120Q 1 R2* * The value of R2 must be selected · from Table 1 or a 1kQ trimpot can be used instead voltage, while the output of the regulator is filtered by a l0µF capacitor to ensure stability. Notice also that the ADJ terminal is bypassed using a second lOµF capacitor, to improve the ripple rejection. D2 protects the LM317 from any reverse voltages which may generated across the output by inductive or capacitive loads, while D3 discharges the lOµF capacitor on the ADJ termi- li:i "'... C> ~ u c,i ov--1 +T2v- D1 ~ 9,oouF + Fig.2: the circuit is shown here wired for a 3V output but this can be varied by changing the value of the 180Q resistor (see Table 1). Mount the LM317 regulator at full lead length & with its metal tab adjacent to the edge of the PC board. Fig.3: here is the full-size etching pattern for the PC board. MAY1992 37 TABLE 2 Brand Plug Size Sanyo 1mm Sony & Aiwa 1.3mm Casio 1.6mm JVC 3.1mm Others: generally 2.1 mm or 2.5mm Note: there is no fixed convention as to which terminal is positive & which is negative. Check the socket of your player - there is usually a small diagram next to it to indicate the wiring polarity The PC board is mounted on the base of the metal case & secured using machine screws, nuts & spacers. Take care with the polarity of the external leads. nal if the output is short circuited. Finally, LED 1 and its associated 3300 current limiting resistor provide power on indication. Construction All the parts are mounted on a small PC board coded SC04104921 - see Fig.3. Begin the assembly by installing PC stakes at the six external wiring points, then install the wire link. You now have to select RZ from Table 1 to obtain the required output voltage. We wanted an output voltage of 3V, so we used a value of 1800 as shown in Fig.3. If you want an output voltage of 6V, for example, just substitute a 4800 resistor instead. The remaining resistors can now be installed, followed by the diodes and the capacitors. Make sure that the diodes and capacitors are oriented ex- actly as shown in the diagram. Finally, the LM317 regulator can be installed. Mount it with its metal tab towards the edge of the board and leave its leads at full length. The completed board assembly is housed in a small metal case which also acts as a heatsink for the LM317 regulator. Mark out and drill the three mounting holes in the base to accept the PC board, then mount the board using 5mm spacers, machine screws and nuts. When the board is in place, mark the mounting hole for the LM317 on the side of the case, then remove the PC board and drill the hole to 3mm. Carefully deburr this hole so that you get a perfectly smooth surface, then reinstall the PC board in the case. Fig.5 shows the mounting details for the LM317. As shown, its metal tab must be isolated from the case using a mica washer and insulating bush. Smear both sides of the mica washer with heatsink compound before bolting the assembly together. When this has been done, use your multimeter (set to a high resistance range) to confirm that there is no connection between the tab and the case. If the meter indicates a short, remove the assembly immediately and locate the source of the problem (eg, a piece of metal swarfmay have punched through the mica washer). Next, attach the adhesive label to the lid and drill a hole to accept the LED bezel. This done, mount the LED in position and connect it to the PC board using short lengths of hook-up wire. Take care with the LED polarity INSULATING MICA WASHER ·"·~)I SCREW r Dllilill(3 ----CASE t T0220 DEVICE The Eliminator Fig.4: this is the full-size artwork for the front panel. 38 SILICON CHIP Fig.5: the LM317 3-terminal regulator must be isolated from the case using a mica washer & insulating bush. Smear all mating surfaces with heatsink compound before bolting the assembly together, then use your multimeter to confirm that the metal tab has been correctly isolated from the case. correct - the polarity indication will usually be moulded into the plastic adjacent to the socket. For in-car use, the input lead is simply a length of figure-8 cable attached to a cigarette lighter plug. Again, make sure that you get the polarity correct. If a plugpack supply is used, tbe input lead will come directly from the plugpack itself. You can either connect the plugpack supply to The Eliminator via a DC socket mounted on the side of the case or you can solder the wires directly to the PC board. The LM317 regulator uses the case as a heatsink. Make sure that it is electrically isolated from the case as shown in Fig.5 . MARK ONE COMMUNICATIONS Specialising in: Mitsubishi , Motorola & NEC mobile phones INSTALLATION & SERVICE 7DAYS . Testing Double check all wiring and component orientation before you assemble the case. All OK? If so, screw the two halves of the case together and connect the unit to your 12V power supply. If everything is working OK, the LED will come on. Check the output voltage and polarity with your multimeter- it should be very close to the selected value. Alternatively, if you substituted a lkQ trimpot for R2 , you simply adjust the pot until you get the desired output voltage. SC - the cathode lead is the shorter of the two (see Fig.1). The assembly can now be completed by installing the input and output leads. These are fed through holes in the ends of the case and secured by cordgrip grommets. You will have to fit the output lead with a DC plug to suit your particular player (see Table 2) . Make sure that you get the polarity obile Phone 18) 29 5888 18) 21 4555 275 Ryedale Rd, Eastwood, NSW2122. Motorola Micro-T•A•C Cellular Telephone Phone (02) 489 7777 Fax (02) 489 7774 Introducing the Protel advantage. Prate({or Windows: Protelfor Windows is an entirely new Printed Circuit Board design system created f or Windows 3. Protelfor Windows brings the professionalism of Protel's proven PCB design sofware to the highly productive Windows 3 environment. 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