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LED Causes Car Computer False Alarm I’m hoping you can help me with a small problem I have. I recently had installed an after-market radio in my BMW X5 and this included a rear-view camera. The camera replaces one of the number-plate lights and has a LED for lighting the number plate. The problem is that because of the lower power consumption of the LED, the car computer thinks the number-plate light is blown and constantly brings up a warning of “check number plate light” on the dashboard. I’m guessing I would need to put a resistor either in series or parallel with the LED to get the car computer to stop nagging me. Can you suggest a suitable resistor value and should it be wired in series or parallel? (B. A., Margate, Tas). • A 100Ω 5W resistor should be suitable and should be wired across the original number plate light connection (not across the camera LED). Presumably this would also be the power connection for the camera. What’s probably happening is that the current drawn by the camera that includes the LED is insufficient for the car computer to accept that the bulb is not blown. If a 100Ω 5W resistor doesn’t solve the problem, use a 47Ω 10W resistor. The resistor should be mounted so that its heat can be dissipated without burning any plastic parts. Mounting it in a small diecast box would be best and you should ensure that the leads are insulated from the case. The resistor should be secured against the box to heatsink it. Some heat resistant epoxy such as JB Weld can be used to affix it to the case or you could attach it using suitable brackets. Advertising Index Altronics......................................... 3 Aust. Exhibitions & Events............ 57 Blamey & Saunders Hearing.......... 5 Core Electronics........................... 33 element14.................................... 69 Embedded Logic Solutions.......... 66 Emona Instruments...................... 67 Front Panel Express....................... 9 Futurlec.......................................... 6 Gless Audio................................ 103 Hammond Manufacturing............... 9 Hare & Forbes.......................... OBC HK Wentworth (Electrolube)......... 65 Icom Australia.............................. 11 Iconic PCB................................... 60 Jaycar .............................. IFC,49-56 Keith Rippon .............................. 103 Keysight Technologies.................. 73 period. An LM3909 can flash a LED while drawing low current. You can purchase the IC and get a data sheet from www.futurlec.com/Linear/LM3909Npr.shtml BFO wanted for shortwave listening Did SILICON CHIP or “Electronics Australia” ever do a project for an external BFO to use with a shortwave receiver? This would resolve amateur SSB transmissions for listeners. A useful addition to your web page would be the ability to search for projects, using supplied keywords. Of course, someone has to index the lot. (D. H., via email). • We have a very comprehensive search facility on our website. Just go to the home page, hover over “Articles” and you will get a choice of searches: contents, word etc. If you type “BFO” into the word search you will get nine results at www.siliconchip.com.au/Articles/ WordSearch and the relevant one is at November 2010 at www.siliconchip. com.au/Issue/2010/November/Highperformance+shortwave+converter This takes you to a preview of the November 2010 issue. The relevant item is in the Circuit Notebook pages of that issue under the title “High Performance Shortwave Converter”. This is suitable for AM and SSB reception from 6MHz to 17MHz. Note that to access this article, you SC need to buy the full issue. KitStop............................................ 6 LD Electronics............................ 103 LEDsales.................................... 103 Lintek Pty Ltd............................... 63 Master Instruments.................... 103 Mastercut Technologies................ 68 Microchip Technology................... 19 Mikroelektronika......................... IBC Ocean Controls.............................. 8 QualiEco Circuits Pty Ltd............. 59 Quest Electronics....................... 103 Rohde & Schwarz........................ 71 Satcam......................................... 70 Sesame Electronics................... 103 Silicon Chip Binders..................... 84 Notes & Errata Playing USB-Stick & SD/MMC Card Music Without a PC, January 2012: on page 86, the article states that the Tenda TD896 requires two 2-pin JST leads for the audio outputs and a 3-pin JST lead for the earphone/ speaker outputs. However, the two 2-pin JST headers/leads are for the earphone/speaker outputs while the 104  Silicon Chip 3-pin header/lead is for the audio (line level) outputs. 40V Switchmode/Linear Bench Supply, April-June 2014: the parts list swaps the part numbers for Q6 and Q7. Q6 is the BC327 and Q7 is the BC337. This is shown correctly on the circuit and parts layout diagrams and on the PCBs we supply. Silicon Chip Online Shop........... 102 Silicon Chip Subscriptions........... 31 Silvertone Electronics.................. 83 Soltronico Pty Ltd......................... 70 Tronixlabs Pty Ltd....................... 103 Virtins Technology.......................... 7 Wiltronics...................................... 10 Worldwide Elect. Components... 103 siliconchip.com.au