Making tachometers and speedometers

If you have some basic electronic skills it is easy to make your own speedo and/or tacho. All modern cars and bikes with analog instruments use tiny stepper motors to drive the needle and these are much more robust than the meter movements found in many after market offerings.

I have just made a tacho for my race bike and I wanted something that looked like 1960/70s Italian race tacho. I got my son to 3D print the housing but that could easily be turned out of aluminium bar. I designed the dial in photopaint and printed it onto sticky backed label paper which I stuck to a thin aluminium backing disc, then I sprayed it with clear lacquer.

To process the input pulses to drive the stepper motor I use an Arduino Nano, because of its small size. If you are interested I am quite happy to pass on full details and my software.

Attachment 45450 Attachment 45451

Attachment 45452

That would be nice for a tachometer for machine tool spindles also.

Definitely interested in the speedo details!
I have messed around with steppers for my lathe's cross feed, unfortunately, the steppers were too small for that. they'd be far, far too big for a speedo, but small steppers are readily available, and cheap.
i don't profess to know a lot about electronics, but I'm good with a soldering iron, I made a couple of digital voltmeters from kits many years ago and I have all the hardware for a hall effect ignition system, just haven't found a good schematic, or the time, to look at it.

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Originally Posted by th62

Definitely interested in the speedo details!
I have messed around with steppers for my lathe's cross feed, unfortunately, the steppers were too small for that. they'd be far, far too big for a speedo, but small steppers are readily available, and cheap.
i don't profess to know a lot about electronics, but I'm good with a soldering iron, I made a couple of digital voltmeters from kits many years ago and I have all the hardware for a hall effect ignition system, just haven't found a good schematic, or the time, to look at it.

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I use a stepper motor "the white blob in the middle of the last photo" that is designed for the job and is used by several OEMs. They are readily available and they are surprisingly low cost. When I bought mine they came in a pack of three. I'll put together a PDF with full details and let you know. Fortunately it was only last week when I assembled the current one so it is reasonably fresh in my mind. I originally designed and built some about 10 years ago. The needles come with the motors and are an orange colour as in the first photo. This is from paint on the back side of the needle which can easily be scraped off and repainted with another colour so if you prefer black or white depending on your background colour it is easy to change. I just found a PDF file with data on the motor, with luck I have managed to attach it to this post. The motors have a movement range of 315 degrees but it is not necessary to use it all if it suits the look that you want with a smaller range on the dial. It is just a question of changing a number in my software.

Attachment 45454

I will be keeping my eye on this for for more details. BUT, I will certainly understand if your other projects get in the way of you creating that PDF.

The trouble with knowing how to do lots of different things and enjoying all of those different things is, there is never enough time to do all of them!!!

As TH62 said, electronics it not my strong suit, but I can follow a schematic!!

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Originally Posted by hemmjo

I will be keeping my eye on this for for more details. BUT, I will certainly understand if your other projects get in the way of you creating that PDF.

The trouble with knowing how to do lots of different things and enjoying all of those different things is, there is never enough time to do all of them!!!

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That is a problem that I know well. I am very bad at making records of what I do. e.g. Although it was around 10 years ago that I first made tachs in this manner it was not until last week that I had to trace through one to make a schematic. I find that it is useful for me to put in the effort, to make PDFs etc of projects, for other people because it gives me a permanent record also.

Are either of you familiar with the Arduino?

I have read a lot about Arduino and have plans to get started, but, time is the factor. In the past, 1980's, I built and programmed some devices to interface with early computers to run motors, record temperatures, and respond to other inputs.

No, I've never used Arduino. I'm not interested in a tacho, just a speedo.

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Originally Posted by th62

No, I've never used Arduino. I'm not interested in a tacho, just a speedo.

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Not a problem, but you will have to just follow instructions to load the software, it is quite easy. Speedo or tacho the hardware is the same it is just a matter of setting a number in the software to suit the number of pulses per sec that you will get from your wheel speed sensor.

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Originally Posted by th62

........ I've bought a magnetic sensor speedo so I don't have a great heavy cable running down beside the fork.

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I have just checked the schematic for my tacho and a speedo will be much easier to wire up. Most of the components in the tacho are for conditioning the noisy signals from the ignition system and you will not need that circuitry. A magnetic or optical wheel sensor will feed directly into the Arduino which feeds directly into the stepper.

Please post a link to the speedo that you bought so that I can check out that the sensor is suitable. Also how do you plan on triggering the sensor? You may be able to do that off the bolts that hold the disc, unless they are non-magnetic stainless. You will get a smoother display with multiple pulses per wheel revolution. It is only a setting in the software to accommodate any number of pulses and the maximum speed that you want to display.

Oh my goodness, this sounds very interesting! I have been looking for an excuse to learn Arduino-ese for the past few years. Was even thinking about learning Python from my grandson to see if I could do sumptin useful. And, now Tony, of all things, you have cast away ESP32 tech to tempt us with the Arduino world!

So here is my problem. It is quite difficult to get good resolution on a high revving engine when all the tick marks are crammed into a 270-300 degree clock face. For example, if a shift point is around 9,500-10,000 rpm, usually everything (in my application) below 6,000-7,000 rpm is useless noise. I would love to display only the top 2,500-3,000 rpm in that same 300 degree window with the correspondly wider tick marks giving much better resolution. My apologies to our motorcycle friends for inferring that 10k rpm was a high number. :D

Also, Tony, this tacho thread may take on a new life. Maybe its own thread would be suitable? And, THAN YOU for your always creative and interesting ideas.

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Originally Posted by Saltfever

.... And, now Tony, of all things, you have cast away ESP32 tech to tempt us with the Arduino world!

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I used the Arduino Nano in this project because they are small and I had some. Also it is a task that the Arduino can handle with ease. Any new projects will probably be done with an ESP32, an Arduino on steroids.

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Originally Posted by Saltfever

So here is my problem. It is quite difficult to get good resolution on a high revving engine when all the tick marks are crammed into a 270-300 degree clock face. For example, if a shift point is around 9,500-10,000 rpm, usually everything (in my application) below 6,000-7,000 rpm is useless noise. I would love to display only the top 2,500-3,000 rpm in that same 300 degree window with the correspondly wider tick marks giving much better resolution. My apologies to our motorcycle friends for inferring that 10k rpm was a high number. :D

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Easy-peasy.

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Originally Posted by Saltfever

Also, Tony, this tacho thread may take on a new life. Maybe its own thread would be suitable? And, THAN YOU for your always creative and interesting ideas.

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th62 I do not want to hi-jack your bike building thread so would you prefer that I move any additional content to a new thread or keep it here? It is your call.

I see the Juken X27 is available on Amazon in various quantities. There appears to be a few flavors, like version, serial number, as well. Is there anything we should watch out for? Will you be making a parts list/schematic available? I'll not post again about this until th62 replies.

13 posts split from this thread: https://www.homemadetools.net/forum/...-rebuild-80821

I have finally got around to drawing the schematic and adding some comments to the Arduino code.
This can be used as either a speedometer or ignition driven tachometer. The software is commented with what needs changing for the different applications.

Lets start with the pretty pictures

Attachment 45595 Click for full size

A wheel sensor, probably Hall effect or other magnetic type could feed 0 to 5 V pulses directly to the Arduino Nano pin 3 but for isolation, level shifting and some noise reduction it is best to use an opto-isolator as shown top right. My original tacho application used a capacitive pickup from a spark plug lead and I used the signal conditioning circuit shown bottom right. I have not tried it yet but I think that might work well with the opto-isolator instead.

Now for the code, if anyone wants to follow this but is not familiar with loading code into Arduinos then do not ask here. Much more comprehensive advice is available in tutorials and guides on the Arduino website and forums here arduino.cc

/*----------------------------------------------------------------------
Adruino firmware to drive an X27.168 instrument stepper motor to use as a tacho or speedometer.
For a tacho application you can just wrap a few winds of wire around the spark plug lead, or get a signal
directly from the ignition system. For a speedo you need a wheel revolution sensor such as a Hall effect
device. See the schematic for more info on this.

There are three defines in the software which set the calibration for individual requirements

#define MAXSTEPS 945 // 945 = (315*3)-> 315 deg rotation * 3 steps/deg
This is a function of the stepper motor which is unlikely to need changing

#define myRange 940 //940 leaves 5 steps buffer against over revving
This sets the range that you want to use. Say you only want to have a swing of 270 degrees then
myRange = 945 x 270/315 = 810. It needs to be an integer less than 940

#define rpmFactor 3760000 // 1000000 * myrange * (60/RPM)=3760000 at 15,000 rpm
RPM is the engine or wheel maximum rpm you want. RPM needs to be multiplied by the number of
pulses per revolution. The value shown is for a maximum of 15,000 rpm on a single cylinder 2 stroke.

In void loop() there is an "if" which cuts the power to the motor when the rpm is low. This is
to save battery life when it is powered by a small dedicated battery. When powered by the vehicle
battery this is not necessary and the whole loop() function can be replaced with the following

void loop()
{
int rpm; // This is not the actual rpm, just the calculated motor position

rpm = rpmFactor/duration;
if (rpm > myRange) {rpm = myRange;} //Limits FSD to prevent skipping steps
stepper.setPosition(rpm);
stepper.update(); // the motor only moves when you call update
} /* end of loop() */
----------------------------------------------------------------------*/

#include <SwitecX25.h> //Library to drive X25/27 168 instrument steppers

// standard X27.168 range 315 degrees at 1/3 degree steps
#define MAXSTEPS 945 /* 945 = (315*3)-> 315 deg rotation * 3 steps/deg */
#define myRange 940 //940 leaves 5 steps buffer against over revving
#define rpmFactor 3760000 // 1000000 * myrange * (60/RPM)=3760000 at 15,000 rpm

//Create and connect a motor called "stepper" to digital pins 8,9,10,11
SwitecX25 stepper(MAXSTEPS,8,9,10,11);

volatile unsigned long duration;
volatile unsigned long startTime;

void setup()
{
// setup pin 3 as an external interrupt. Input from ignition
pinMode(3, INPUT) ;
attachInterrupt (digitalPinToInterrupt(3), GetTiming, RISING);

setZero(); // Zero stepper needle
startTime = micros();
} // end of setup

void setZero() //Set stepper motor to zero
{
stepper.maxVel = 40; // Set slow for zeroing against stops
stepper.currentStep = 950 ;
stepper.setPosition(0);
stepper.updateBlocking() ;
delay(500); /* To let it settle at zero for 0.5 sec. */
stepper.maxVel = 2000; // I have no idea how fast it can go, but this is enough
}// End of setZero

void GetTiming () // interrupt service routine
{
unsigned long endTime;

endTime = micros();
duration = endTime - startTime ;
startTime = endTime;
} // end of GetTiming

void loop()
{
static int hasSlept = 0 ;
int rpm; // This is not the actual rpm, just the calculated motor position

if (duration > 250000) // if < 4 Hz or < 240rpm. Increase number for speedometer use
{
hasSlept = 1;
digitalWrite(8, LOW); // Switch off power to motor to save battery
digitalWrite(9, LOW);
digitalWrite(10, LOW);
digitalWrite(11, LOW);
}
else
{
if (hasSlept == 1){
hasSlept = 0;
setZero();
startTime = micros();
}
rpm = rpmFactor/duration;
if (rpm > myRange) {rpm = myRange;} //Limits FSD to prevent skipping steps
stepper.setPosition(rpm);
stepper.update(); // the motor only moves when you call update
}
} // end of loop()

-------------------------------------------------------

Hello Tony - MANY thanks for your ongoing supply of fascinating and informative posts. Been a fan since I wanted (never got :-( ) one of your frames back in the day :-)
I'm a bit of a 'Nano' fan - and I've been trying to put together a program to drive shift lights. There are a number already out there - but the various different approaches only serve to confuse (me).
Having been told in no uncertain terms that my bike racing days are over - these days I amuse myself with little single seaters in hillclimbs and sprints. Never have sufficient time to LOOK at a rev counter - and to be honest can't even see the thing because you're hunkered down so low :-)
Both cars are relatively high revving - based on Suzuki GSX R600 (K7) and GSX R1000 (K6) the former peaking out at 15K.
So - the question is:- do you think the approach you have used measuring the duration between ignition pulses via an interrupt is as good as it gets ? And hence applicable to my project too ?
(600 uses original Suzy electronics, and the 1000 runs a dedicated ECU from MBE)

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Originally Posted by vasquito

Hello Tony - MANY thanks for your ongoing supply of fascinating and informative posts.

So - the question is:- do you think the approach you have used measuring the duration between ignition pulses via an interrupt is as good as it gets?

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As good as it gets? That seems a strange question. It drinks pulses synced to a rotary speed and displays an analog scaled representation of the measured frequency. What more do you want? Are you questioning the accuracy. Well it is digital all the way through to the display but then it relies on the accuracy with which the scale was drawn, the alignment of the pointer and our eye's ability to read it. The interrupt will have some latency and there will be the usual +/- count error, but those are smaller than any display/reading errors. There are basically two methods to measure frequency in this context.
1. Measure the time between pulses, which you question.
2. Count how many pulses you get in a set time. I used this method around 50 years ago because with the discrete components available then it was the easiest way. However, it tends to give a jerky reading. You can smooth it out by using a very short capture period but then accuracy suffers. A long period gives a jerky meter movement and if acceleration takes place during that period, the reading will be the average over that period and not the value now, so accuracy suffers.

Hi Tony - tricky this electronic text communication isn't it?
I think that I simply didn't do a good job of asking the question.
Having reviewed a number of other designs for shift lights, I've seen code written to count pulses and divide by time, to do it twice in order to ignore any spurious results - and several other variations.
The question I was TRYING to ask ( :-) ) was: do you consider the interrupt method to be the most appropriate and accurate method for measuring pulse frequency ?
I was NOT querying the accuracy of your implementation - just looking for "reassurance" that this is, indeed, the way to go.
Obviously the rest of your code doesn't relate to my application, but the two interface suggestions will come in handy as well.
My thanks again.

Quote:

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Originally Posted by vasquito

Hi Tony - tricky this electronic text communication isn't it?
I think that I simply didn't do a good job of asking the question.
Having reviewed a number of other designs for shift lights, I've seen code written to count pulses and divide by time, to do it twice in order to ignore any spurious results - and several other variations.
The question I was TRYING to ask ( :-) ) was: do you consider the interrupt method to be the most appropriate and accurate method for measuring pulse frequency ?
I was NOT querying the accuracy of your implementation - just looking for "reassurance" that this is, indeed, the way to go.
Obviously the rest of your code doesn't relate to my application, but the two interface suggestions will come in handy as well.
My thanks again.

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I think that I answered that with my response labelled "2" in my previous reply. For a shift light you want to know what the RPM is NOW or at least no more than one engine revolution before. Counting pulses in a set time works fine for constant speed or slow acceleration.

I'd be very interested in getting a copy of this PDF and software.
Thank you

Bill Whitney
bwhit5@yahoo.com

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Originally Posted by bwhit5

I'd be very interested in getting a copy of this PDF and software.
Thank you

Bill Whitney
bwhit5@yahoo.com

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The software is in a previous comment.

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Originally Posted by tonyfoale

I use a stepper motor "the white blob in the middle of the last photo" that is designed for the job and is used by several OEMs. They are readily available and they are surprisingly low cost. When I bought mine they came in a pack of three. I'll put together a PDF with full details and let you know. Fortunately it was only last week when I assembled the current one so it is reasonably fresh in my mind. I originally designed and built some about 10 years ago. The needles come with the motors and are an orange colour as in the first photo. This is from paint on the back side of the needle which can easily be scraped off and repainted with another colour so if you prefer black or white depending on your background colour it is easy to change. I just found a PDF file with data on the motor, with luck I have managed to attach it to this post. The motors have a movement range of 315 degrees but it is not necessary to use it all if it suits the look that you want with a smaller range on the dial. It is just a question of changing a number in my software.

Attachment 45454

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I'm definitely interested in making either the tach or speedometer. Waiting for more

Just a quick one - your Nano schematic shows +5V power coming out to sensors etc from pin 28 - which is actually a Reset and 5V out is from the adjacent pin 27 (as actually indicated on your diagram - but not 'connected').

Quote:

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Originally Posted by vasquito

Just a quick one - your Nano schematic shows +5V power coming out to sensors etc from pin 28 - which is actually a Reset and 5V out is from the adjacent pin 27 (as actually indicated on your diagram - but not 'connected').

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You spotted my deliberate mistake. I'll fix it and repost. Thanks for the heads up.

Here's a quick one:

Attachment 45599

Impressive. Does it read electrical pulses from the ignition of does it read some kind of mechanical or magnetic input? I'm asking because I have a 1967 John Deer backhoe with no tach and, since it's a diesel, no electrical pulses to read. This maybe would fit the bill.

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Originally Posted by nhengineer

Impressive. Does it read electrical pulses from the ignition of does it read some kind of mechanical or magnetic input? I'm asking because I have a 1967 John Deer backhoe with no tach and, since it's a diesel, no electrical pulses to read. This maybe would fit the bill.

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This explained in previous posts, particularly #15. I will be making another post soon discussing more detail on input options.

The only post I see are yours and mine. Que pasa?

Count me in for those plans! The speedo in my '96 Mustang Cobra is flaky, so after I do a bunch of other work on it I'll tackle that.

Tony, did you post a link for the code? I have been trying to understand how to use a stepper for a indicator, with out any success.

Ralph

Can you see page 2, post number 15? Tony's code is posted there. At this point in time there are 4 pages to this thread. For those wanting a PDF go to the top of this thread and look for the tab called "thread tools". Select "show printable version" which will change what you see to a text format. (which strips out HTML or any other weird embellishments). Copy and paste into what ever you want.

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Originally Posted by Ralphxyz

Tony, did you post a link for the code? I have been trying to understand how to use a stepper for a indicator, with out any success.

Ralph

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The code is in post #15. That should show you how it's done.
However, that is the code from a few years back and the display starts from zero. I need to prepare another tacho with a range more compressed so last night I modified the code to make its use more flexible and while I was at it I tidied up a few things. The changes are small but I need to test them before posting the new code. I will put that in a PDF for the whole project, that will make it easier for anyone who wants to follow it rather than piecemeal posts. So that will incur a few days delay.

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Originally Posted by Saltfever

Can you see page 2, post number 15? Tony's code is posted there. At this point in time there are 4 pages to this thread. For those wanting a PDF go to the top of this thread and look for the tab called "thread tools". Select "show printable version" which will change what you see to a text format. (which strips out HTML or any other weird embellishments). Copy and paste into what ever you want.

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Or just wait a few days and I'll have a PDF prepared without all the irrelevant content that you get in a long theme.