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Midnight programming
July 17, 2006
Midnight programming alerts homeowner of potential theft
Robert Reavis needed to build a ramp for his home's front entrance over a weekend. After measuring and cutting wood until 11:00 pm on Saturday night, Reavis was too tired to go on. He was also too tired to move the unused wood to his backyard, but feared that thieves might take the wood from his front yard if he left it out overnight. What does a test engineer do after playing carpenter all day but wants to protect his valuable redwood? Build a burglar alarm, of course.
Reavis used a DMM, a computer with a modem, some lamp cord, and a resistor to call his cell phone if anyone attempted to steal his wood. "I clamped the wood together with a pipe clamp into a single object too heavy to carry and ran the lamp cord wire from my lab to the wood," he explained. "I looped the wire around and through the pipe clamp so that it can't be removed without cutting, and soldered in a 1500-ohm, half-watt resistor at the end of the wire." He then connected the wire loop to the inputs of a DMM and connected its IEEE 488 port to a computer in his lab.
Using Agilent Vee, Reavis wrote a program to monitor the resistance. If the value remained between 800 ohms and 3000 ohms, he knew the wire was intact. If the DMM measured a value outside of that range (indicating a short or open circuit), the modem could dial his cell phone and hang up after 30 seconds. He quickly found the modem commands online and wrote his program in about 20 minutes. Reavis completed the deck the following day. See photo.
Reavis also supplied his Vee source code and a PDF document containing a screen image. Download a zip file contianing both. --Martin Rowe, Senior Technical Editor.
Robert Reavis is a daytime Fare Collection Engineer at the San Francisco Bay Area Rapid Transit District and a nighttime test engineer at his company, Warm Springs Computer Works. In between, he's a carpenter, plumber, electrician, and roofer (a homeowner).
Posted by Martin Rowe on July 17, 2006 | Comments (3)
