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Motorbike Gear Displayer Help and Ideas

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Hi all, for my electronics project this year i have considered to design and make a gear displayer for my Honda CG 125 motorbike. Since my bike doesn't indicate what gear i'm in, it will also come in handy for myself to use after my electronics course has finished. My first ideas on how to go about things are as follows...

Input - My foot triggering moving some sort of switching device to be attached to the gear peg.

Process - not to sure on this. Maybe a closed loop system that checks what gear im currently in, and if its changed to change the output displayed

Output - LCD display.

I have considered using just LED's for the output, but since this is a project for A2 I need more 'active conponents'

These are just my initial ideas so please comment all you want. As i need as much research/help as possible. I think the main problem will be with finding a method that works to use as my input. (dectecting the gear change)

Implementing an up/down counter triggered by micro-switches or reed relays is simple enough.
However finding the actual position of the gear selector shaft is a bit more tricky, its buried in the gearbox and the only way in is to split the crankases.There may be a way to fit some kind of feedback position sensor but without a service manual it is imposibble to say.

If memory serves me correct , is there a neutral position switch ? that could be used as a reset/reference for an external counter.

LCD might be a bit difficult to read under certain conditions
A seven segment LED display would be better 1 n 2 3 4

Pay particular attention to your power supply, those little Hondas use a horrible flywheel magneto arrangement , single diode rectifier and a relay voltage regulator.... :idea:
If the problems Tansis mentioned are insurmountable, here's a harebrained idea:
Use a microcontroller (you probably need one anyway). Take the ratio of engine RPM to rear wheel RPM and convert to gear number using an algorithm and/or a look up table. During and shortly after shifting, you would want to inhibit changes in the display, probably controlled by the position of the clutch actuator.
I think you are on to something there Ron H
The use of a micro-controller to compare the engine RPM to wheel speed is a brilliant idea .
The instrument cluster could be replaced with a digital display giving RPM , MPH , selected gear and Odometer reading. Time clock etc
It's fairly common on engine dataloggers too use this method. Engine rpm compared to wheel speed. It would not be hard to adapt a wheel speed sensor from a car to the motorcycle, on all cars with ABS, there is a seperate sensor for each wheel, which is easily picked from a junkyard.
hey guys thanks for the feedback so far! Some great ideas! I'm kinda noobish so i need some help explaining the help i got so far :oops:

First answer is: Yeh the bike has a netural position.

Second answer: My project is flexiable so i could just make it into a Tacho.

My first query: Could you possibly explain how the micro-controller would get the engine RPM and the Wheel spin? I have never used micro-controllers before.

Second: Where would I connect it?

Third: Is the setup described like a bike speedo. Where i attach a magnet thing to a spoke on my wheel rim?

I need help :( hehe
L3wis said:
My first query: Could you possibly explain how the micro-controller would get the engine RPM and the Wheel spin? I have never used micro-controllers before.

Second: Where would I connect it?

Third: Is the setup described like a bike speedo. Where i attach a magnet thing to a spoke on my wheel rim?

I need help :( hehe
I'm new to this too, so don't take anything I say as gospel or the best way to do this.

To get very basic, a microcontroller is like a small computer on a single chip. It allows digital (and sometimes analog) inputs. You can program it, like any computer, in assembly and sometimes C or BASIC, and output signals from it. The PIC, and Atmel lines are popular.

You can use two LM2907 chips which convert signal frequency to a voltage level, that's easily read by the microcontroller with an analog to digital input. If you do a google search you can find the lm2907 datasheet and application sheet, which does a good job of describing it's function, and how you might implement it.

One LM2907 would be used to convert the signal going to the ignitor or points system into an RPM signal (I assume the bike is not new enough to have a electronic ignition with crankshaft trigger inputs).

The other LM2907 could be used to determine wheel speed (or final output speed). The type of wheel speed sensor you use, is up to you. Like I said, you can pull these sensors out of late model cars at junkyards. The ABS ones are usually small incased sensors and trigger wheels. The Honda ones I work with have a 5volt input, ground, and signal output. You just have to find some way of turning the trigger wheel.

Your microntroller would be programmed to read these two inputs and you can decide on an output type. LEDs that light up on gear position, LCD display that actually displays RPM and gear, anything you can figure out. My own Tacho that I'm working on for my racecar will be using an RC servo controlled by the microcontroller to turn an indicator needle and reproduce an analog RPM gauge.

With the microcontroller you can also implement other features pretty easily, like an over rev warning indicator. Read other sensors like temperature sensors, and even do some type of security start, or anti-theft system.
wow thanks for your help. If u had said the word pic i would have understood :D I'm understanding it all a lot more! And its starting to sound possible :) On the Electric start of things im not to sure. Some pointers that might help:

- My bike doesnt have a electric ignition switch, like on mopeds. My Honda only has a kickstart.

- On my honda one the honda sticker there is a mentioning of electronic start or something. I'll check this tommorow morning. Could this create problems?

Thanks so far!
I think using LM2907s is unnecessary. All you need is a rear wheel once-around pulse as a gate for counting the engine ignition pulses. In other words, count the engine pulses, and each time the rear wheel pulse arrives, read the count with the PIC (or whatever) and then reset the counter and start counting again. You could do this with the PIC unless it ties up its resources too much, in which case you could do it with a CMOS counter or another PIC.
The rear wheel pulse can be derived with a magnet on the wheel (you might want to counterbalance it if you put it out near the tire) and a Hall-effect device or reed relay. It could also possibly be done optically, although I would worry about dirt and ambient light. The ignition pulse you can get from the points, if it has them, or possibly from the magneto or capacitively coupled from the spark plug wire (I have no idea what sort of ignition system your bike has).
Yeh sounds like good ideas. After reading the last post a few times makes sense. Once i have all the counts, would i have them all going into another pic that i can then calculate different things using different formulars. Like the gear i am in, MPH, Distance travelled?
Could be a real money-spinner of project , motorcycle electrics are long overdue for bringing into the 21st centuary. Digital instrument clusters are still rare on motorbikes as tou progress you might begin to use your aging CG125 for fuel injection (indirect) and engine management experiments. :idea:
Or perhaps in the meantime LED brake and indicator lamp conversions 8) coded keypad alarm/ignition would be VERY usefull............... :wink:
[see manual for how ignition switch ACTUALLY functions] Handy to know if you should ever lose the keys. Tis why bikers invest in heavy chain and large padlock.(D type rigid bar type locks a waste of money)
I build V-8 powered trikes as a hobby,(obsession my wife says) , and one of the first units I had was for a trike built around a Harley. I used a hall sensor at the neutral position to sense the shift lever displacement, (missing event detection), and a hall sensor above and below the normal at rest shifter position to sense direction of shift. By adding or subtracting a count for each shift change, and by using the direction of shift to control the operation (+/-), you can keep a running count of where you are. This allows simple logice to detect, determine and light an appropriate led to show gear position.
MC Project

Hi Lewis - If you decide to use the shifter as a means of detecting position you would be best to attach your position sensor to the shaft itself. The lever vibrates quite a bit. Also you will find that there is very little radial movement between gears in the shaft..... There are forks, detents and rods inside the case but that would make your project more mechanical than electrical. I am by no means an electronics wizz but I have worked as a MC mechanic. Let me know if I can help. Good Luck. You might just invent something that is marketable. -Stick
Cool ideas ppl trikebuilder Thanks for the info on using sensors. I think i might advance on the pic idea thought because using pic's for my project is part of the syllabus and should gain me high marks. Once i get going this should be a really good project! If successful how would i market it?
From what you're saying, it sounds like you want to use multiple PICs. A single PIC would be able to do everything you need here, including frequency counting.

I think you should still stick with the Freq to Voltage conversion chips. Even though they aren't necessary, it will simplify implementation for you. The programming will be pretty simple, a loop comparing the 2 Analog signals and turning on the specific output pins based on the speed inputs. Making a frequency counter, though not all that difficult, would require more programming knowledge.

There's enough amateur PIC articles out there that you should be able to get through it on your own.
Cool thxs for your response. Where can i buy Freq to Voltage conversion chips and how much are they usually. And can you get them programable in most languages. I think i can only gain access to assembly software. So i think it will have to be wrote in assembly also.
You can get the lm2907 and lm2917 from for less the $2.50 each. The datasheets with sample circuits are on the national semiconductor site. These are not programmable chips. They simply convert a frequency to a voltage level that can be read by an analog to digital input. To make it easier, I would choose a PIC with built in A2D.

Hi all again... I've decided to change my project into just a tacho for my RPMS. I've been experimenting in crocodile technology with microcontrollers and stuff. What i can't work out is how to get a output from the microcontroller. And how to then display that value in 5 7 segment displays? As for the input side of things i seem to be ok.

Thanks in advance.
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