The ECU Is Just A Very Complicated Switch

The first switch to find its way onto a motorcycle was the ignition system’s mechanical contact breaker. Send current into a primary coil to create a magnetic field, then suddenly stop that current. The magnetic field collapses, inducing a high-voltage into a secondary coil of many turns of fine copper wire wound over the primary. Connect that secondary across a spark-plug gap, and you have a source of timed ignition for an internal ­combustion engine.

How do we stop the current at the right time? Place a cam on the engine’s crankshaft or camshaft, arranged so that the cam bumps open a pair of switch contacts just before the piston reaches top dead center.

Racers and others needed a reliable means of stopping a running engine, and the result was the “kill button.” In its most reliable and basic form, this was a short length of springy hacksaw blade, taped to the handlebar and arranged so that when the rider pressed it with his or her left thumb, it shorted the ignition primary coil to ground, causing sparking to cease.

Those who thought fancier switches—it’s Mil-Spec, man!—were cooler were so often rewarded by failure; little switch parts ­vibrated loose and failed, with the hacksaw blade switch never dying out.

Motorcycle electrical systems allowed lighting for night operation and a horn for hazard warning. In the attempt to provide this to the British motorcycle industry, Joseph Lucas Ltd. earned the name “prince of darkness” for the frequency with which its early electrical gear failed from the vibration of motorcycles.

On familiar British magnetos, the contact breaker often spun as a part of the wire-wound armature, operated by a stationary cam that encircled it.

MV Agusta and Benelli ­four-­cylinder roadracing engines through the early 1970s were able to make do with points-and-cam magnetos adapted from US-made Mercury Marine racing outboards, but by the late 1960s, magnetos were falling behind in their ability to supply the necessary number of sparks per second.

Fortunately there was a ready answer: the transistor, a form of switch implemented in the solid state, with no moving parts. Instead of a rotating cam to time the ­ignition sparks, a variety of noncontact timing devices appeared. In a transistor, placing a weak signal on its “gate” was able to switch on or off a much stronger current.

There was more. In 1962, my ­college roommate showed me a 6mm “top hat” with wire leads projecting from it.

“This,” he intoned rather pompously, “is an integrated circuit. What’s in here is not just a transistor like you find in a portable radio. This is a group of transistors, all manufactured on the same little chip of silicon, and connected together to perform a logic function.”

Neither of us knew then that every 18 to 24 months, the number of transistor switches it was possible to photo-etch on a given area of silicon would double. As a result, a common smartphone has roughly 100,000 times more processing power than the onboard ­computer that directed the 1969 Apollo ­landing on the moon.

In 1969, the Spanish Femsa transistor-switched self-generating CDI ignition appeared, to replace the 1940s magnetos and mechanical contact-breaker switches (or “points”) on Japanese racing motorcycles. Poof! Points ignitions disappeared.

All engine tuners knew that a fixed ignition timing, such as 36 ­degrees BTDC, or 2mm BTDC, was a compromise that sacrificed ­power. Much better would be a system holding a complete ignition curve in memory, listing the best-torque timing for each rpm. ­Transistor switches, encoding data in the form of digital on/off states, took new form as computers and electronic data storage to ­implement this and much else.

The first I saw were alternate ignition timing maps for a 1980s Aprilia 250 race bike, selected by dip switches. Then it all came with a rush—whatever control concept you could imagine, there were suddenly ways to implement it. The compromises imposed by analog methods were broken.

With the proliferation of ­devices in vehicles came ever-thicker wire bundles and more-complex ­multipole switches by which to control them. In 1985, Bosch provided a better idea to Mercedes: the ­Controller Area Network bus system. Instead of running power to each device from a central switch, this system connected all devices—lights, window controls, power seats—to a single bus. Each device contained its own tiny computer. Each device recognized its own coded signal, telling it to switch itself on. Each signal is assigned a priority level to eliminate ambiguity. Today, every aspect of a vehicle—touchscreens, navigation, stability control, adaptive cruise control, engine management, tire pressure, semiactive suspension—is processed by a computer.

Given the existence and low cost of microcomputers (which are just orderly arrangements of switches), it’s hard to think of a better way to handle complex controls. No one person can comprehend the onrushing future of digital controls and data management as new ­concepts emerge daily—all ­mediated by switches.