Yet Another Motoduino! Gearhead plays with soldering gun.

Looking to build an all-in-one speedo/tach to replace the chrome dash for my 1993 yamaha cruiser. I have read the other motorcycle threads here and have found some information, but nothing from start to finish. Previous Owner did a number on the stock mechanical speedometer and tachometer as well as the housing for the indicator lights. There are a few aftermarket choices but these options aren’t right for my budget. I am starting from scratch but I am an objective-based learner.
I am in the process of acquiring an oscilloscope to read tachometer signal from the TCI. Planning to use an Uno for this as its power needs are compatible. So far the shopping list is:

  • uno
  • led rope for tachometer
  • servo to drive needle for speedometer
  • gps reciever preferably in the >=5HZ refresh range to drive speedometer and log route
  • Breadboard for prototyping
  • adafruit oled for use as odometer/tripometer and for the dummy lights on dash(Brights, Oil, Left/ Right Turnsigal, Neutral and Fuel
  • light/backlight for speedometer for night driving
  • Weatherproof housing to store all components
  • SDCard to log route/mileage
  • coffee
  • beer

GPS logging is not a must, and I’m open to reed switches or hall effect sensors for speedometer if the GPS latency is too bad. Pretty excited to get started but if you think I missed something or have any input, its all appreciated.

So far the shopping list is

You forgot the whiskey, you idiot! 8)

GPS logging is not a must

I'd just add a commercial GPS which already does the logging and speed calculations and shows maps, etc.

How does the current mangled speedometer get data? Is it mechanical? My Harleys haven't used mechanical means since the 90's.

Hey Paul, good catch on the whiskey! Right now the speedo is a 2:1 mechanical but its been abused to the point where it reads 85mph when I'm going about 40... I hadn't thought about using a dedicated GPS, I will look into it. Looking into adding a usb charging point off the battery (with a relay through the ignition or headlight so its not always on) for my iPhone, is there any reason I couldn't run the Arduino off the same usb plug? My thinking is that it would be a little safer than wiring it directly, but I defer to those with more experience.

is there any reason I couldn't run the Arduino off the same usb plug?

No, and that is safer (and quieter) than running it off 12V.

I looked into some of the commercial GPS applications and saw some possibilities but nothing really awesome for the same price point. However I have been looking into the Venus GPS that claims 20hz on the datasheet but I found a comment saying

The 20Hz feature is of limited use. With 100ms apart, two packets arrive back to back with absolute zero space between. This means the first in each pair is at least 50ms late. If you configure it for 10Hz, packets are properly spaced 100ms apart. This quirk is true for both NMEA and binary.
GGA is the only message that is sent faster than 1Hz. All other NMEA types are sent at 1Hz, regardless what update rate you configure.

However further down another commentator says

The 20Hz positions are accurate in that the position data corresponds to the location at the specific time given, however the messages will be delayed (sometimes over 200mS) from the PPS output. If you need to correlate some other event, use the PPS. (On my motorcycle logger, I reset a millisecond counter using PPS and mS-stamp the engine messages). RMC, GLL, GGA, VTG are all sent at the 20Hz or other value but can be throttled with another setting. The satellite status (GSV/GSA) is sent at 1Hz.

Can somebody make heads or tails of this data sheet and let me know which is correct? I'm not sure there is any virtue in a speedometer that updates 20 times a second or just once a second. Surely there must be a middle ground?

That Venus638FLPx does indeed have 2 consecutive 20Hz NMEA data coming out together in 10 bursts every second. SkyTraq says it's due to some internal scheduling that I couldn't understand. Now they have a new 50Hz capable Venus838FLPx that have NMEA data coming out in 50 bursts every second.

High GPS update rate mostly good for performance logging like RaceLogic's VBOX or for smooth scrolling map display with marine chart plotter on speed boats. For speedometer and to log route, 1Hz should be be good enough.