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Advertising Index Altronics....................loose insert,111 Amateur Scientist CD..................... 77 Cleverscope................................... 10 Dyne Industries................................ 6 Embedded Logic Solutions............ 25 Emona Instruments........................ 13 Geoff Coppa................................. 111 Grantronics.................................. 111 Hare & Forbes............................ OBC Circuit Ideas Wanted High Profile Communications....... 111 We pay up to $100 for contributions to Circuit Notebook, or you could win a$150 gift voucher. Silicon Chip Publications, PO Box 139, Collaroy, NSW 2097. Instant PCBs................................ 111 the motor noise can be reduced. You set it to the frequency where the motor makes the least noise associated with the PWM switching. The June 1997 controller would require the oscillator components to be altered to adjust the frequency. We recommend using a 100nF capacitor at pin 5 of IC1 and a resistance value ranging from 10kΩ up to 100kΩ at pin 6; a 100kΩ trimpot could be used. While noise will never be completely eliminated with such a pulse width modulated controller, the noise can be reduced by selecting the optimum frequency. The frequency can be adjusted from 100Hz to 1kHz or thereabouts. Note that the higher frequencies may not provide a linear speed control but SC this depends on the motor. LED Sales.................................... 111 DOWNLOAD OUR CATALOG at www.iinet.net.au/~worcom WORLDWIDE ELECTRONIC COMPONENTS PO Box 631, Hillarys, WA 6923 Ph: (08) 9307 7305 Fax: (08) 9307 7309 Email: worcom<at>iinet.net.au Ask SILICON CHIP . . . continued from p110 immobiliser, your idea may well be feasible but we have not produced any suitable circuitry. Motor is noisy with PWM speed control I built the 12V 10A speed control kit. It works fine but there is a very loud 2kHz tone coming from the motor. It is just a 12V fan but the tone is louder than the motor! Can you give me some advice please? (G. F., via email). • We are not sure if you are referring to the controller from June 1997 or from June 2011. The June 2011 controller has frequency adjustment so that Issues Getting Dog-Eared? Keep your copies safe with these handy binders Available Aust. only. Price: $A14.95 plus $10 p&p per order (includes GST). Just fill in and mail the handy order form in this issue; or fax (02) 9939 2648; or call (02) 9939 3295 and quote your credit card number. Buy five and get them postage free! 112  Silicon Chip Jaycar ................................ IFC,53-60 Keith Rippon................................. 111 Kitstop.............................................. 8 LHP.NET.AU................................. IBC Microchip Technology....................... 7 Mikroelektronika............................. 11 Ocean Controls.............................. 12 Quest Electronics......................... 111 Radio & Hobbies DVD.................. 109 RF Modules.................................. 112 Roc-Solid......................................... 5 Sesame Electronics..................... 111 Sethna Electronics....................... 111 Silicon Chip Binders..................... 112 Silicon Chip Bookshop................. 103 Silicon Chip Order Form.............. 105 Silicon Chip Partshop................... 104 Silicon Chip Subscriptions............. 52 REAL VALUE AT Siomar Battery Engineering...... 3,111 P&P Switchmode Power Supplies.......... 65 $14.95 PLUS Splat Controls.............................. 111 Tekmark......................................... 29 Truscotts Electronic World............ 111 Verbatim Lights.............................. 51 Wiltronics......................................... 9 Worldwide Elect. Components..... 112 siliconchip.com.au