A Digital Tacho For A Harley

If you are a lover of motorcycling, you’ll probably fit into one or other of the distinct groups of riders. Maybe you’re a sportsbike lover always trying to get your knee down, a supermotard who gets their knee down without trying, a trailie rider for whom tarmac is an annoyance between real rides, or a classic bike enthusiast who spends more time in the workshop than riding.

[Xavier Morales] is none of these, for he cruises the roads of his native Catalonia on a Harley-Davidson Sportster. If you’re familiar with Harleys only from popular culture, or you’re a sportsbike rider who derides them for anachronistic handling and brakes, it’s worth taking a look at a modern Harley from a technical standpoint. Despite styling and brand ethos that evokes another era with the trademark large V-twin engine that looks to the untrained eye the same as it did decades ago, today’s Harley is a very modern machine, and much more capable than the sneering sportsbiker would give it credit for.

There is one area though in which [Xavier]’s Harley was sorely lacking. Its single instrument was a speedometer, it had no rev counter. You might think this would be less of an issue with the lower-revving Harley engine than it would be with a Japanese sportsbike that exists in a hail of revs, but it was annoying enough to him that he built his own tachometer. His write-up of the project is both lengthy and fascinating, and well worth a read.

The Sportster’s data bus follows an established but obsolete standard, SAE J1850 VPW. Since driver chips for this bus are out of production, he had to create his own using a transistor and a couple of resistors. Once he has the data he feeds it to a PIC 18F2553 which in turn runs a display driver chip controlling a brace of 7-segment LEDs. There are also a set of LEDs to indicate gear changes. The whole is installed in a 3D-printed housing alongside the original speedometer, behind the glass from another dial. As a result it looks as though the bike was always meant to be a two-clock design, with a professional appearance.

If you’d like to see it in action, he’s posted a few videos, and we’ve put one below the break. The beautiful Catalan scenery and the mountain twisties look very inviting.

If bikes are your thing then we’ve featured quite a few over the years. Memorable though are this gas-turbine monster, and this disastrous first attempt at frame building.

Filed under: transportation hacks