One of the impediments for aspiring engineers (students and others) is that so many of the projects they might want to build are “too much.” They require special, often hard-to-obtain components, they are physically difficult to build (too much complexity, plus those tiny components), they have critical layout and placement issues, troubleshooting requires relatively costly tools and test equipment, observations are nearly impossible. . . . I could go on, but you know the problems as well as I do. And when all is built and tested, it's not clear what the project does, there is no satisfying, tangible “clunk” or real-world application for many of them, other than drawing nice pictures on the PC screen, typically.
That's why I was pleased to see a great basic project in the August 2009 issue of QST , the primary publication of the Amateur Radio Relay League (ARRL). The article, “The Ignition Switch” solves a problem when using the car's 12-V system to power external electronics: the turn-on and turn-off transients of the supply rail can fry ordinary electronics (amateur radios, power converters, small TVs, and similar). The circuit provides a 10-second delay after the ignition is turned “on” which allows the supply rail to stabilize, and equally important, a 5-minute power-off delay after the ignition is turned off, so you can finish what you were doing and also avoid load-dump transients. [Note: the article is not available online except to subscribers, so you'll have to find a coworker who belongs to the ARRL, or go to the local public library; many of them subscribe to QST .]
I liked everything about this project. The BOM is basic: it uses two CMOS 555 timers, two 2N3904 transistors, and a 12-V relay, plus some passive components, all easy to obtain. Layout is not critical. It implements an understandable and useful function. Perhaps best of all, you can observe what it does internally, and at its input and output, simply by using a voltmeter, since the timing is so broad–and you can hear the satisfying clunk of the relay pulling in or dropping out.
So, if you have a potential EE in your circle, or you want to re-discover the joy of a basic, tangible, satisfying project that requires no software, no development system, no fancy “tools”, and no extreme or frustrating contortions, check this one out. ♦