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.

35 thoughts on “A Digital Tacho For A Harley

  1. “today’s Harley is a very modern machine, and much more capable than the sneering sportsbiker would give it credit for.


    The Sportster’s data bus follows an established but obsolete standard, SAE J1850 VPW. Since driver chips for this bus are out of production”

    Yeah – cutting edge stuff those Harley engines. If you want to pay loads of money for an awful bike that makes you look like an accountant with a midlife crisis, then go ahead.

    If you want to look at American bikes at the opposite end of the technology scale, try Zero. I got a FXS electric supermoto recently and absolutely love it.

  2. Another gadget that is useful but not necessarily following the ethos of what Harley is all about. Harley is all about the feeling, the sensation. Its a mixture of pure power, vibration and pull. You don’t need dials and clocks a seasoned rider knows the bike and feels through the bike when to change. Technology can determine your ride, why? be free, in the sixties they understood this.

    1. In a similar way, I had a good feel for the speed of my Suzuki Sidekick (manual transmission) through the vibration, and noise level at various speeds. But when I would drive my wife’s car, (automatic transmission) I would have to be mindful of the speedometer, for if I drove attempting to reach the same noise/vibration level, I was speeding.

    2. Thanks brother….I’ve ridden nothing but a 1200 Sportster for yrs. Have never rode anything bigger and dont need to. I know my bike and I’ve rode it all over America without a problem. No fuel guage, tach or anything other than stock and I’m happy whistling down twisties, hwys and back country roads.

  3. All bickering about Harleys aside (they make my knuckles bleed..the result of a previous life with a ’72 FLH), the build should get kudos for a couple of reasons, not least because it’s apparently [Xavier Morales] first build and he suffered through all the rookie nonsense to get it all hung together. Also it’s not just a tach but has a rev sweep bar and a fuel gauge – pretty well done all in all.

  4. I ride a Harley, love it. Have just over 30k miles on it. Bought it with 15k. Bought it 3 years ago, and put that 15k on her. No issues at all.
    Each rider likes what they like. I dont see the need to buy a bike that can do 180 mph, when I cannot do 180 mph. What I DO like is the comfort of the bike, the sound, and that I can ride for hours in comfort. If I wanted a fast bike, I certainly wouldnt go Harley.
    But, I wanted reliability, and comfort. I got both of those. Not to mention, EVERYONE can work on a Harley. In the event something breaks, I can call up a dealership, and get it worked on. Chances are, they have the parts available. There are upsides and downsides to any bike choice. Depends on your taste, thats all.

      1. Does seem odd, and in the old days it probably wasn’t true what with oil leaks and numerous problems brought on by excessive vibration but my Harley and been more reliable than any Japanese bike I’ve owned and far more reliable than my BMW.

    1. Not true… Friend of mine broke down on a cross country ride, Harley Dealer would not touch his 1995 UltraGlide because “it is too old”

      he had to find a small one man bike shop to fix it, and had it trailered to the next town to get it fixed. It’s not just harley, ALL motorcycle dealers are refusing to work on older bikes as they like hiring cheap young guys to work for them instead of the Old guys that actually know something about motorcycles but demand $50 an hour. I had to teach a Yamaha Shop’s “lead tech” how to syncronize 4 carbs.

  5. I have a non-contact handheld tachometer for fixing my scooters. Now I’m thinking wouldn’t it be easier to just build a custom 3d printed housing for the digital tachometer, and hook a permanent power supply to digital tacho unit and mount it near the speedo? Wouldn’t that be a much easier route than building a new thing based on an obsolete protocol? Don’t they go obsolete for a reason?

    I have a 16-year-old Triumph that’s probably “outdated” by today’s standards, and even that bike have a pretty comprehensive diagnostic and tuning tool with a fairly sophisticated ECU and Fuel Injection system (with a tachometer)

    I salute Xavier’s efforts but the article sounds a little biased and confusing (modern technology and obsolete standards)

    Cheers & Ride Safe.

    1. According to the article, Harley introduced that data bus in 2001, and it was reasonably current at the time.

      Nicely done – I like the idea of a Sportster, but wouldn’t own one myself because I don’t like how the air cleaner keeps poking me in the leg.

  6. Awww… you can’t talk bikes without the subject wandering… They’re about freedom, not discipline!

    Hacking something together that might give out on the highway isn’t my thing. Bikes need to keep going, so keep it stock. All I’ve added is a well regulated properly fused USB outlet. But a lot of bikes do lack a tach, so this is quite interesting. Also, speedo cables do break, and when they do all you have left is the tach to give clues to your speed. A great mod would be a hidden switch to flip tach to display MPH for the top gear. And charging voltage is HIGHLY important, so an idiot light for that as well, it’s dead simple. I ride winter too and would like to know road surface temp so an IR non-contact idiot light could go on warning of ice possible. Too bad can’t also look ahead and warn of wet manhole covers, they’re slippery! They should carve a traction grid into the surface of them instead of the city name, put city on the bottom side ’cause we already know what city we’re in!

    Grew up trail riding abominations I built. Just hate when the ride ends simply because the road did so got myself a KLR650. 85 mph is the highest speed limit I’ve seen in the US and it does that well with full camping gear plus passenger. Water crossings up to the seat deep and it’s a tall bike. It’s oft used by folks for those around-the-world trips. It’s built like an old tractor, meaning meant for the farmer to be able to fix pretty much everything that goes wrong right on the side of the road. 6.1 gallon tank at 47-55 mpg for 250+ non-stop range. I carry spare fuel tubing and help out those Harley riders that “customized” themselves into a .5 gallon blinding bright chrome tank then ran out of gas. Inexpensive bike too! Can buy 5 of them new for what a typical Harley costs. Not dissing Harley at all… just want to ride and ride and ride, do the woods, desert, without stopping. Look up TAT (Trans American Trail). 14 days in Grand Canyon last year. Saw a sign “Caution- Cougar Crossing”. Colorado, snoozed next to tree and when woke saw sign on other side of tree said “Caution- Grizzly Bear Area”.

    Did used to own a Harley once too… lol… the Street and Trail 125 back in the 70’s. Not even red loctite would keep it together. Lost a passenger footpeg about every 100 miles. After first 3 mo the Harley dealer kept a whole box of them in stock just for me! A quirk of that one model?

    Full respect for any choice of bike. Loved my moped! Be careful with a moped though, it’s a gateway drug to a full bike. Great learning tool though! Taught my son about wet leaves on inside of corners!.

    A GPS that would warn you of unexpected tight corners in the mountains would be great. Guardrails up there are great for keeping the bike on the road, but low enough the rider goes right over!

  7. As another member of the Quad Cam Junkies club, I say thanks!
    I was using an OBDII scanner plugged into the Data Port, but this would give me just the basics, without all the extra information that can wait until I’m back home.

  8. Xavier, you’re just scratching the surface. Lots of motorcycle riders like me are technoheads, otherwise I’d be on a Bergman. I want a line of gauges that gives me speed, odometer, trip meter, engine speed, gear position, oil pressure, oil temperature, oil level, head temperature, amps, volts, ambient air temperature, wind speed, wind direction, altitude, time, and maybe I’ve missed something. Is that too much to ask?

    1. A traffic avoidance radar maybe ?
      While it’s nice to have the dash to look like a jetfighter one, remember airplanes usually allow time to look at the panels because they have nothing on their path. Except when landing. Then you need to focus on the outside, not on the panels !

  9. A cool project, but why on such a bike ?
    HD engines are mostly made for leisure, not performance, so a tachometer seems overkill imho.
    One more word about the display : an LCD display should be more readable in full sunlight and only requires the standard back-light at night.


    1. Back in 1980, I rode my Yamaha RD200 to work along with a cow-orker on his Harley.
      At 50 mph my Yammer was going ZEEEEEEE! and his Harley was going thum-thum-thum.
      At 60 mph my Yammer was going ZEEEEEEE! and his Harley was going thum-thum-thum.

  10. I ride a 2006 Harley Ultra Classic. I ride it because it’s what I want and the style I like. My exhausts are true duals but not terribly loud. I dont need to be doing 100 plus miles an hour or up on the rear wheel. But i can get on it and ride 1500 miles stopping only for gas. Its all preference, but in the wind. If you want a tach, get a tach, but i dont need to be into the rev limiter to enjoy riding.

  11. I once made an electronic analog tacho for my motorcycle out of 3 LM3914 IC’s and 30 LEDs arranged in an arc in the original case.

    After about a month it started giving weird readings around 11,000 RPM.

    After a couple more weeks it basically vibrated itself to death lol.

    Then there was that time that I installed an auto eject cassette player …

  12. Urg. I would not really want a tach on my Harley, and if I did put a tach on it the last thing I would want would be one with a digital readout. A nice analog tach might be acceptable. The other question is why in the world screw around with the bikes data but for something you can get much more brainlessly from the engine itself? All that being said, if it makes the dude who built it happy, power to him. We all have our tastes in things.

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