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Analog Angle Article

Goodbye, my DMM; it’s been fun, but we’re pretty much finished

One secondary effect of the pervasiveness of sophisticated electronics into every application niche is that our traditional hardware tools are no longer very useful. Not too long ago, all you needed to check out most of a car's electrical system was a digital multimeter (DMM) to measure relatively static voltage, current, and resistance. Nearly every circuit was either an on/off loop or a 12-V analog loop. The DMM could tell you just about everything you needed to know.

But today's car is a highly sensored, networked system. Every vehicle since 1996 has built-in ODB II (On Board Diagnostics Version II), so you need a code scanner to find out what the check engine light indicates about immediate or impending problems. Some shops, especially dealers, also have protocol analyzers for the LIN and CAN busses which are becoming the car's nervous system.

This pervasiveness has expanded to truly specialized niches. For example, the typical home alarm system now uses a digital protocol between the control panel and the user keypad, as well as between sensors and control panel, so an analyzer is needed for many problems. Even the modest hobby of model railroading has been affected.(see Model Railroader magazine, www.modelrailroader.com, or The National Model Railroad Association, www.nmra.org) through the industry's adoption of standardized DCC (Digital Command Control).

Since its inception over 100 years ago, these models, like autos, used a simple dc loop for on/off as well as powering the motors, with motor voltage and power literally delivered via the rails (no pun intended). The system had limitations and reliability issues, especially when the locomotive was in low-speed operation with the rail under 1 V. It also required a profusion of independent power blocks and wiring so that multiple engines could run at the same time on the layout. Despite the “cost” in wire and performance, the setup was easy to test and troubleshoot even for non-engineers (the world of most modelers); all it took was a DMM and wiring diagram.

After several false and painful starts, DCC is fast becoming the dominant way of running the (model) railroad, due to the operating advantages it offers. It offers in-field programmability, which lets the user configure locomotives for desired primary and secondary operating characteristics, instead of having them set by the vendor's hardware design (hmmmmthis sounds very familiar!).

But now, the modeler has to have the know-how to set these parameters properly in advance, and there are many options among which to select, before you can get that loco rolling along the track. No longer can you run it right out of the box. A DMM won't do it, either; you may need a unit such as the $179 DCC Protocol Analyzer from Pricom (www.pricom.com) to find the tricky problems: it even measures bit error rate, packet errors, and other communications-link parameters. Things have certainly changed.

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