Fullscreen HTML5Med Res (??MB)HTML4

Speed Alarm won’t limit car speed Could the PIC-based Speed Alarm described in the November & December 1999 issues be used to limit a car’s speed in a similar way to the PIC Tachometer described in April 2000, which limits the revs via an immobiliser? I guess my question really is “Can the Speed Alarm be interfaced with the immobiliser circuit with only software revi­sion?” Your help would be appreciated. (S. A., via email). • The Speed Alarm is not suitable to actually control the speed of the car. For this you need a cruise control as it re­quires a means to manipulate the air flow to the engine via the carburettor or throttle body in a fuel injected car. Enhanced plugpack power supply I remember a very useful circuit that I’m sure I saw in SILICON CHIP magazine but I’ve looked all though the circuit list­ings and can’t find it. It was a simple circuit to reduce mains hum when you’re using a “plugpack” power supply with any sort of audio device. I thought it was in the “Circuit Notebook” section. (M. C., Eight Mile Plains, Qld). • The article was in the December 1998 issue, entitled: “A Regulated 12V DC plugpack”. Universal battery charger differences I am trying to find out what the differences are between the original and Mk.2 versions of the Universal Battery Charger. Can you help? (C. S., via email). • The main differences are that the Mk.2 version has facility to charge Notes & Errata PC-Controlled Mains Switch, September 2001: to avoid the possibility of electric shock from contact with the power plug’s pins when it is disconnected, a 100kΩ 0.5W resistor should be connected across the Varistor. This will discharge the 0.1µF 250VAC capacitor. Also, to improve the voltage isolation of the PC tracks around the optocoupler, it is recommended that neutral cure silicone caulking compound be applied to pins 4-6 of OPTO1 and the nearby component pads. Pardy Lites, December 2001: the resistor following D1 should be 820Ω instead of 4.7kΩ. Both the circuit on page 68 and the PC board on page 69 have this error. Audio/Video Distribution Amplifier, November 2001: there is an error in the underside copper pattern for the PC board which causes both audio outputs from the fourth socket pair from the right-hand end (looking from the rear) to deliver the R channel output signal. The problem can be fixed fairly Lithium-Ion batteries and there are more voltage ranges available for charging Nicad and NiMH batteries. Also the tenden­cy for the Mk.1 charger to prematurely terminate charging for older batteries has been corrected. You can upgrade the Mk.1 version to the Mk.2 version by transferring the components from the old board to the new PC board. This PC board is coded 14302982 and is available from RCS Radio Pty Ltd. Phone (02) 9738 0330. Hardware items such as the case, easily. First, remove the PC board assembly from the case and turn it upside down with the output connectors on the top. Then locate the fourth audio output pair from the left and verify that the pads at the lower ends of the two output series resistors (originally 47kΩ, now 1kΩ) both have tracks connecting them to the upper ‘R’ signal line track – unlike all the other output pairs. Cut the track on the right and, using a short length of tinned copper wire, connect the resis­tor pad to the lower ‘L’ signal line track instead. Solar Power Battery Charger, March 2002: the MJE2955 labelling for Q2 and Q3 on the overlay diagram on page 85 is incorrect. They should be labelled MTP2955. (Note that an MTP2955 is a P-channel Mosfet while a MJE2955 is a bipolar power transistor). The circuit and parts list are correct. In addition, the parts list incorrectly specifies a 4011 for IC1; it should in fact be a 4093 quad Schmitt trigger, as shown on the parts overlay diagram. the transformer, mains and battery connection wiring, heatsink and rectifier are unchanged. The front panel is changed slightly to accommodate the extra battery type and ranges. Of course, it is not necessary to in­clude all the extra voltage ranges provided by the Mk.2 version or include the Li-Ion selection. Main parts changes are the addition of a 2-pole 4-position rotary switch in place of the DPDT toggle switch used for S3 and some resistor changes. SC 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. www.siliconchip.com.au April 2002  93