With winter approaching again, give yourself extra warning of treacherous road conditions

When the author first saw the Vehicle Frost Box by Steve Dellow in the Jan 2000 EPE, he was immediately taken with it, and soon knocked one up and installed it in his car.

Steve’s Frost Box was designed to indicate the external temperature by means of a dual colour red/green l.e.d., and warn when black ice on the road was likely. The l.e.d. was designed to show green above 4ºC (when ice formation is presumably unlikely), red between 0ºC and 4ºC, and flash alternately green and red below 0ºC. The temperature sensor was nothing more complicated than a simple signal diode.

Several things about the project seemed interesting: the economy of the temperature sensor (components don’t come much cheaper than 1N4148 diodes!), the simplicity and effectiveness of the red/green diode display, and the cleverness of the design in contriving three different display patterns corresponding to different temperatures, were all factors. Plus the author’s ageing car was not equipped with a thermometer, so it was a useful project anyway.