Fullscreen HTML5Med Res (??MB)HTML4

• A subwoofer controller with auto power on was published in the December 1995 issue of SILICON CHIP and it was available as a kit from Altronics in Perth. The MiniVox could also be modified as you suggest but the relay must have adequate ratings to switch the motor current. Kit availability for FM Radio Intercom I am interested in the FM Radio Intercom for motorbikes, published in about 1990 I think. Just wondering would you still know if this kit is available or another is made to replace it? (J. E., via email). • The kit is no longer available and the LM381 stereo output stage chip is now obsolete. If you wanted to substitute another output stage you can still get all the other bits. It was de­scribed in October and November 1989. We can supply the relevant back issues at $7 each, including postage. Charging a 4.8V NiCd battery I recently constructed the Fast Battery Charger which ap­peared in the February and March 1998 issues of SILICON CHIP from a kit. The charger project provides for five nicad battery types to be charged. In a modification published in SILICON CHIP in June 1998, you suggested using a 12kΩ and an 18kΩ resistor in parallel to provide for a 4.8V battery. It was suggested that this replace the 14.4V provision. As switch S5 has six positions I would like to add the 4.8V modifi­cation as an extra value to other five. However, when I added the two resistors between the switch and the PC board the output voltage appears too high and the “Fast” charge Notes & Errata Line Dancer, May 1999: diode D10 on the circuit diagram on page 18 is shown the wrong way around. Its cathode should connect to pin 2 of IC2. and the 0V rail. Alternatively, wire a switch in series with the output so that the track is not connected when power is first applied to the controller. Model Train Controller, April 1997: to avoid a problem with the loco moving backwards for a short distance when power is first applied, the 4700µF capacitor connected between switch S1 and the -12V rail needs to be modified. Instead, two back-to-back 4700µF 25VW capacitors should be connected between the common terminal of switch S1 FM Radio Tuner Card, June 1999: the board numbers and “SC” logo on the PC artworks (page 26) will short out unused pins in the ISA slot on the motherboard if left intact. To avoid this prob­lem, remove the board numbers and logo from the artwork before etching the board. Suitably modified patterns have been posted on our web site. LED lights instead of the “No Battery” LED as with the other values. Could you please advise whether the 18kΩ and 12kΩ resistors are correct for 4.8V and whether any additional modification needs to be done. (D. M., Auckland, NZ). • Unfortunately, the modification published in June 1998 to use 12kΩ and 18kΩ resistors in parallel to allow charging of 4.8V batteries is incorrect. In order to charge 4.8V batteries a resistance of 28kΩ should be used for the extra switch position. This value can be obtained using two 56kΩ resistors in parallel, a 27kΩ resistor in series with a 1kΩ or an 18kΩ resistor in series with 10kΩ. SINAD measurements explained I would like to know if there has been an article that explains the difference between S/N (signal-to-noise) and SINAD measurements? (R. S., via email). • SINAD stands for “signal plus noise and distortion” and is a measure of signal quality in a communications receiver or link. We published an article on the subject in the November 1988 issue. We can supply a photocopy of this article for $7 including postage. Engine immobiliser transistor needed Where can I buy the MJH10012 transistor used in the Engine Immobiliser Mk.2 featured in the December 1998 issue. I can only find the metal version. (D. L., via email). • If you have built a kit and the transistor has failed, you should be able to buy it as spare part from the retailer who sold you the kit. Failing that, Oatley Electronics has a plastic TV line output transistor which will probably do the job. It is the 2SD1554 and they have them at around $3. Phone them on (02) 9584 SC 3563. WARNING! SILICON CHIP magazine regularly describes projects which employ a mains power supply or produce high voltage. All such projects should be considered dangerous or even lethal if not used safely. Readers are warned that high voltage wiring should be carried out according to the instructions in the articles. When working on these projects use extreme care to ensure that you do not accidentally come into contact with mains AC voltages or high voltage DC. If you are not confident about working with projects employing mains voltages or other high voltages, you are advised not to attempt work on them. Silicon Chip Publications Pty Ltd disclaims any liability for damages should anyone be killed or injured while working on a project or circuit described in any issue of SILICON CHIP magazine. Devices or circuits described in SILICON CHIP may be covered by patents. SILICON CHIP disclaims any liability for the infringement of such patents by the manufacturing or selling of any such equipment. SILICON CHIP also disclaims any liability for projects which are used in such a way as to infringe relevant government regulations and by-laws. Advertisers are warned that they are responsible for the content of all advertisements and that they must conform to the Trade Practices Act 1974 or as subsequently amended and to any governmental regulations which are applicable. AUGUST 1999  93