Adding a digital pushbike speedo to a motorbike

[mike-s]

Two months ago i bought a generic pushbike speedo, but i've already come across 5 severe limitations
1) it can only show speed or time at once, not both.
2) you have to push a button to cycle between the modes to alternate
3) theres a couple of other modes such as trip distance and total odometer distance that you have to cycle through to get to the above, a good way of being distracted.
4) no backlight.
5) it only goes up to 99kmh (or mph)

In order to fix this i've had to go and buy a new one, but new ones run the light off the battery, an effective way of killing your button battery quickly. So i bought the following one off ebay.


I bought it a month or so ago, it shows your speed all the time, and you can alternate between total distance, trip distance and time (it would be rare that i would need to do so, so it'd stay on the time/speed setting 99% of the time), it goes up to 199km/h and has just enough room that i can fit some silicon & micro LED's in there to wire it up to the bike power supply.

This trip meter can do any wheel size from 10cm to 4m diameter, and i'm going to use it with twin low profile rare earth magnets (from a hard drive) glued to the front wheel for accurate speed resolution (I find only one magnet goes you a delay of about 1 to 1.5 seconds on speed readout).

Anyway last week i bought a bunch of red green & amber surface mount LED's (4mm long 1.5mm wide, 3mm tall) to try out different colours, a (N4004 1Amp/150v) diode and 2x 1.2k resistors (running in parallel to get it to 510 ohm), and basically i hooked them up yesterday to the bike speedo & gave it a dummy run.

Quick tests show it's looking quite promising, it looks bright enough and illuminates the screen rather well in even the daytime. I now need to hook it up to a detatchable switchblock (if i ever decide to unplug it etc) and mount it on the dash of my bike.

to be continued....

[mike-s]

incidentally i went with the Amber LED's as of the Surface mount LED's available (green, red or amber) they seemed to be the best colour for visibility.

[Johnnie5]

what made you choose this one over say a sigma unit ?

[mike-s]

I was half doing this for fun, and couldnt find a "reasonably priced" unit that had backlighting (and considering i was planning from the outset to modify the unit to allow permenant backlighting it allowed for more fun in experimentation

I initially bought a second hand sigma unit, but it turns out that it was a sealed unit, and i screwed it up in the process of attempting to split it, and as it turns out there wasn't really any provision for a place to put the LED's as things were so tightly packed in the unit. Whereas this one was a cheap buy on ebay ($18 shipped from hong kong), also has a lot of room on the sides, has 4 small phillips heas screws on the back of it and it takes no more than 30 seconds to take it apart.

I figured that at the worst if i screwed this up, with the ebay sale i was going through, i'd still get a pushbike headlamp and taillight out of the deal if i fucked it up a second time.

oh and the fact that the plastic was clear made it a bit of an easier choice in buying as i knew the light placement wasn't as critical as the plastic would allow the light to to pass through.

as a side note, I have ended up painting the outside plastic with a couple coats of black enamel paint to make sure the LED's themselves don't distract from the light illuminating the screen.

[mike-s]

Here's an approximate schematic of how i connected it together, also this is the calculator i used to figure out the correct value resistors. Remember to plug in 14.5v as the voltage used to account for the higher voltage with the motor running.

n.b. the closest "correct" rating resistor to the required 500ohm is a 560, but i couldnt get hold of a 0.35 watt rated one, only 0.25 watt ones. so i got two 1.2k ohm 0.25 watt resistors and ran them in parallel to double the wattage and get a reasonably close resistance.

[Rossi]

Can I ask why ?

[mike-s]

One simple reason "because". That and the speedo's aren't 100% correct and i wanted to improve on that if i could. That and i wanted to add light to it so it would be useful at night.

[Yankee]

GREAT IDEA!!

Love to see the actual finished product pics! I did the "cat-eye" on my bike some years ago and it's been great (magnet on my rear tyre). Found the same limitations as you (display annoyances, lighting, time lapse in measurement, etc.)
few Q's:
The two magnets? Do you then have to divide the wheel circumference by two only? or some sort of derivative of pi and the C?!?!?!
Took me forever to find a bloody unit that would go over 110kph!
can't wait to see the lighting set up and detachable plug-in to the dash!

good job!

[mike-s]

in order, yes, just devide by two. measure it up to make sure they are exactly opposite, i'd hate to think what kind of speed "jitter" you'd get if they were over 3mm out, 110, wait 109, 110, 109 (id go mad myself).

its not so much a detachable plug, but moreso a plug so that i can remove the power to the LED's on a whim.

more to come soon, im going to bed now, was up all night for work and frankly im shattered.

[photomike666]

Can't you buy a speedo healer for about $130, does basically the same thing with a sensor on the wheel and another on the gearbox somewhere? Then you dash speedo is accurate, and you don't need to bugger around with the bikes electrics.

I like the idea though. I got the kids speedos for their BMXs, they read upto 199kph, and have a function where you can enter the circumference of the wheel to get an accurate reading.

[javaman]

Brilliant! But how hard do you have to pedal

[Johnnie5]

Can't you buy a speedo healer for about $130, does basically the same thing with a sensor on the wheel and another on the gearbox somewhere? Then you dash speedo is accurate, and you don't need to bugger around with the bikes electrics.

I like the idea though. I got the kids speedos for their BMXs, they read upto 199kph, and have a function where you can enter the circumference of the wheel to get an accurate reading.

well thats $130 and can only be fitted to an electronic driven speedo , so if you have a cable driven speedo you are outta luck

Sigma speedos have been around forever and available for sub $40 a couyple of rare earth magnets from Jaycar so sub $50 and they go 300+ KPH

imho who needs the light, i dont ride at night and even if i didonce you have installed the speedo you can easily know how much your original speedo is out or of course use the tacho

the side benefit of having a pushbike speedo us the various different functions they come with, max speed etc

[plane]

I've been running a Sigma BC1200 on my bike for 2 uears now (still on the same battery).

No back light, but for $25 plus a rare earth magnet, a cheap little toy!

Cheers,
Pete

[Wattie]

i had one on my Xr600, the cable speedo was a fair way out when you went from a knobby to a road tyre on the front.

i wasnt as high tech as mike, i juts battled seeing it at night.
as i did with the road anyway, (trailbike headlights suck)

it went up to like 300k also, the xr only saw 165 but.

dad and i stuck one on his buell, and it saw 240K.

no backlight but

[mike-s]

well to be honest, the significant reason i want it there is so that i've got a clock. The other half is just to be able to know specifically as the speed increments on my speedo are bloody close together (goes to the better part of 300km/h). and why add a backlight? simply "because i know im able to do it".