Camchain and tensioner seen up close in a cutaway bike engine

Home Repair And Restoration

DIY Trip Meter

Post Received 3 June 2020

By Mark Noel

My Honley MTR125 is a faithful recreation of the legendary Honda CG125 and is very well equipped but with the exception of a trip meter. Most folks will, I am sure, agree that such a mileage counter is essential for estimating your remaining fuel range or for calculating miles per gallon. As with a wife, I decided that I could not live without one and so set about designing my very own. A trip meter that is, not a wife.

One option is to fit one of those electronic bicycle gadgets which serve as a speedo and odometer amongst other things. They count wheel revolutions via a fixed Hall sensor and magnet on the wheel but that would require more wiring and bits to fix to the fork, wheel and handlebar. The option I describe here is manual-input and much simpler, being based on a miniature three digit BCD edge switch - a type of encoder switch with up/down buttons for each digit which appear in a small window. The BCD switch used in this project was sourced from ebay and is shown in the picture.

A simple 3 digit display with buttons to set the digits to the number you require
BCD Switch. Buttons to set the number as required.

I designed a mount that clamps to the ignition key stalk and extends to a housing for the BCD switch, with a hinged lid and window to keep out dust and water. An oval recess is included for a label reminding me of the range to reserve (420 km in the case of the Honley). The great thing about 3D computer modelling is that the whole assembly can be viewed from all angles and the lid hinged back and forth to check for fit. Once the model was deemed to be OK then each part was saved as a special file that was sent to my Ultimaker printer for creation in PLA plastic. It took about 3.5 hours for the machine to print the PLA components.

A 3d digital rendering of the housing that mark will print out
3D computer model of the trip meter.

The photograph shows the two 3D printed parts (housing & window frame) and other bits from my scrap box that complete the unit. The redundant 5 pin PCB connectors were cut off before assembly and the finished trip meter is shown mounted on the little Honley.

The printed out housing, the bcd switch and several screws, nuts and bolts
Components of the DIY trip meter.

Each time I fill up with petrol I note the odometer reading (say 1326 km), mentally add the range figure, then use the + and - buttons adjacent to each digit to show the distance when I will next  run down to reserve: 1746 km in this example. Of course it is always prudent to fill up before reaching this terminal value but it is very handy to have a reminder close to the speedometer.

The meter in a 3D printed plastic housing, attached to the key barrel of the motorcycle
Assembled and mounted trip meter

If your bike already has a trip meter then a unit like this could instead be used as a memo for other data, such as distance to the next B&B or filling station.

By now you will be wondering what 'BCD' stands for: it is an abbreviation for 'Binary Coded Decimal', a digital convention whereby a 4 bit number (plus ground) is used encode the numbers 0 to 9, hence the 5 pin connectors. In this convention my birthday in MM-DD format is written as:

[0000 0001]   [0001 0101]

I look forward to receiving your birthday greetings on the relevant day - in binary of course!

Send in your own useful(?) gadgets. Click here.

Reader's Comments

Ren - The Ed¹ said :-
Thing is, I'd need a calculator to work out whatever plus range...
24/06/2020 09:23:37 UTC
Ian Soady said :-
That might be a good idea for the Norton as it doesn't have a trip meter (some previous owner fitted a WD speedo). On the other hand it's easy enough to open the filler and have a quick shufti inside.....
24/06/2020 11:18:16 UTC
Snod said :-
I just remember the three digits you'd put into the new counter, is it really so hard? I'm yet to reset a trip meter, too fiddly/dirty..
24/06/2020 11:26:32 UTC
Ian Soady said :-
Come to think of it, it's like those stitch counters that knitters use. Hmmmm......

They seem to come in only 2 digit versions but I could have 2 in fetching harmonised colours.
24/06/2020 11:26:42 UTC
Ren - The Ed¹ said :-
I just can't see you fitting 2 of those stitch counters to the Norton Ian, that's the sort of bodge that I'd do.

What does "harmonised colours" mean too? Is that like when Sharon talks about cushions that match the curtains? To me the word "match" speaks of a short splinter of wood used as an incendiary so I just see cushions that set fire to curtains. It sounds very dangerous and I certainly would not want to "match" anything on my motorcycle.
25/06/2020 08:15:44 UTC
Bob said :-
I like it, a simple solution that is quick and easy to use - and therefore you will use it.
25/06/2020 01:11:52 UTC
CrazyFrog said :-
I did something very similar, but possibly less elegant on an old MZ. My local 99p shop sold cheap and horrible combination locks for bicycles. I stripped one down and used 3 of the numerical wheels mounted on a bolt with a wing nut to loosen it off for adjustment and a bit of suitably bent wire as a pointer. 99p and bobs you uncle!
29/06/2020 06:53:54 UTC
Ren - The Ed¹ said :-
Now you're talking my kind of language CrazyFrog. Mind you, where would I find 99p from? Not made of money you know (I only sleep on it).
29/06/2020 08:52:25 UTC
Borsuk said :-
In the same vein as the Soviet answer to Americas $1,000,000 pen developed during the space race. Write previous odometer reading on the speedo glass using chinagraph pencil.
03/07/2020 12:49:29 UTC
Ren - The Ed¹ said :-
I had to look up chinagraph pencil. Personally I'd use a permanent marker on the tank and when I've run out of space to write on the tank I'd just repaint it using some quarter-empty tin of matt emulsion in "shades of summer" lime green. I'm stylish like that.
03/07/2020 07:50:47 UTC

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