A helping hand: 64-bit counter design pays off, slowly

Early in my career, I designed several kinds of signal demodulators, including AM, FM, and PM devices. Two of our standard building blocks were analog multipliers and discrete integrators. My boss was moving, albeit slowly, from analog to digital techniques, so he and I looked at simple ways to make a digital equivalent of these two blocks.

After four months’ effort on what we thought was a simple design, my boss called it quits. I used most of the parts from our attempts in other projects and threw away the rest—except for a pair of MAC (multiplier-accumulator) ICs.

In those days, we designed with 74XXX and 74LSXXX MSI counters, registers, and gates. The MACs were TTL (transistor-to-transistor logic), 838-bit-multiply, 64-bit-output devices, specially ordered for this application. In power consumption, they made the 74XXX stuff look like CMOS, so my boss didn’t see where we’d use them in any other projects. I kept them, however, thinking of various ways they might be useful. One day, while looking at their data sheet, I realized one would make a fast 64-bit up/down counter.

I presented the idea to my boss. His first reaction was to stare at me. Then he warned, “It’s too big. It uses too much power. It’s too expensive.” Finally, he asked, “Don’t you have something useful to do?”

Intimidated, but not defeated, I further developed my idea and ran a few tests. The design worked beautifully. However, when I showed it to my co-workers, reactions varied from loud yawns to inquiries of “Is that all it does?” Lacking other encouragement, I submitted it to EDN as a Design Idea. The magazine accepted it.

I put the matter aside and forgot about it. Then, almost a year later, I received a call from an engineer who had questions about the circuit’s operation. He needed a 64-bit counter for a box he was designing for a NASA (National Aeronautics and Space Administration) satellite. My idea not only saved board space, using one 100-pin IC rather than 16 16-pin ICs plus wiring, but also simplified the board layout, which meant easier testing and lower cost.

I didn’t receive any awards or pats on the back, but my idea did help another engineer; that kind of satisfaction goes a long way. I’d like to believe that my other published Design Ideas have helped others, just as those I’ve read have helped me—especially when six cups of black coffee lose their effect on the meetings and paperwork, and I need something new to perk me up.

Steve Lubs has been an engineer in a variety of roles at the Defense Department for 30 years and has always argued with his bosses. Like Steve, you can share your Tales from the Cube and receive $200. Contact Maury Wright at mgwright@edn.com.