RPM reading 12v to 5v

Projects General Guidance
1

Hi All

I’m fairly new to Arduino and I’m currently working on a project where I need to read RPM from my Bike.

Looking at the wiring for my bike the coil is triggered by a ground breaking switch in the CDI unit. I’m hoping to use that pulse for RPM input as it pulses once every revolution.
I want to leave the original circuit as untouched as possible to not interfere with the running of the bike.

The RPM gauge gains a pulse feed by supplying 12v to the gauge and the ground running through the same ground switch as the coil.
I’m thinking I can wire in the same way and use the grounding switch as my pulse, however there seem to be many ways of doing that and converting the 12v to 5v.

The research I’ve done seems to suggest an optocoupler is best, like the H11L1M. I’ve attached a diagram of how I think it could be wired in, would this work or would a mosfet be better?

Basically need some guidance on how best to wire this in, and how to select resistors etc

Thanks in advance!!

IMG_0322
IMG_03221920×1080 226 KB

2

So your bike engine is 2-cycle and you have to add oil to the gasoline for engine lubrication. Right?

3

No it’s a 4 stroke but it has two coils each driving two cylinders, so ends up being one pulse per rotation if using output from one coil

4

Ok, that makes sense. Does the CDI unit not have an unused tachometer connection?

5

Measure speed using weighted, rolling, wheel circumference for distance traveled per revolution.

6

The easiest way would be to use a current clamp on the primary side of the coil. This way there is no modification to the vehicle.

image
image474×266 30.6 KB

7

Unfortunately no spare output, there isn’t even an actual dedicated one for the tach, and measuring speed doesn’t help with rpm measurements unfortunately.

@gilshultz
I like the idea of the induction clamp, however do you know the frequency response? At 12k rpm it’ll need to be registering 200hz

8

Sorry... I was thinking "rpm of wheel" after seeing "bike"... you have a motorcycle.

9

You could first test your optocoupler idea by replacing the optocoupler with an LED and a 1 K resistor.

10

Are you sure it is CDI (Capacitive Discharge Ignition) ?

11

That is dependent on the device you use. I have probes that go well over 100 MHz. You might want to build your own: https://www.edn.com/build-your-own-oscilloscope-probes-for-power-measurements-part-1/ 200Hz. should not be a problem.

12

Yeh I might try the optocoupler with a led first, I also have a spare coil to experiment with.

Yeh pretty sure it is a CDI, it’s a 2003 Suzuki bandit, could be wrong

The last link there has gone straight over my head, not sure what I’m looking at aha

13

Your schematic and written discussion leads me to think you are confusing a CDI system with the old ignition systems that used a cam driven switch to open and close and produce the spark from the coil. You will benefit from asking Google how a CDI actually operates. There are no points/switch that causes the spark from the coil.

14

Hi, a quick check with Google.

The 2003 Suzuki Bandit (both GSF600 and GSF1200 models) uses a digital/transistorized ignition system.

Key details of this system include:

  • CDI/Igniter Unit: The system is controlled by an electronic igniter unit (often referred to as a CDI box).
  • Coils: It utilizes dual ignition coils.
  • Firing Order: The system typically uses a wasted-spark configuration, where coils fire on both the compression and exhaust strokes, often for cylinders 1/4 and 2/3.
  • Components: The system relies on a pulser coil (sensor) located on the right end of the crankshaft to send timing signals to the igniter.

For the 2003 GSF1200S Bandit, the ignition is officially listed as "Digital/Transistorized".

Tom.... :smiley: :+1: :coffee: :australia:

15

CDIs charge up a capacitor to several hundred volts then discharge it through the coil. Watch out.

16

Looking online seems like it’s not a true CDI
It uses a kind mosfet to trigger the coil the same way an older points ignition system would work.
So it has a separate igniter box like a CDI but doesn’t work like one!

17

So, why not copy the schematic you found and post it here so we can see it also.