Question about vehicle tachometer circuitry

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Discussion Overview

The discussion revolves around designing a circuit to read RPM data from an onboard ECU tachometer for a racing car project. The focus is on interpreting a square wave output from the ECU and displaying the RPM using LEDs, with considerations for accuracy and refresh rates.

Discussion Character

  • Technical explanation
  • Debate/contested
  • Homework-related

Main Points Raised

  • One participant describes the need to design a device that reads RPM from a motorcycle engine's ECU, which outputs a square wave signal.
  • Another participant suggests starting with frequency counters and decade counter ICs, but emphasizes that the original poster should do the bulk of the work.
  • Some participants mention that there are various methods to measure RPM, ranging from simple to more complex, but accuracy specifications were not provided initially.
  • One participant notes the need to measure frequencies from 20 Hz to 200 Hz, corresponding to RPMs from 1200 to 12000, and suggests a refresh rate of around 500 ms to avoid LED flickering.
  • There is a clarification that the project is not for school credit, but academic teachers are involved in guiding the students' work.
  • A later reply indicates a decision to implement the solution using Arduino.

Areas of Agreement / Disagreement

Participants express differing views on the appropriateness of providing detailed circuit designs versus guiding the original poster to do their own research. There is no consensus on a specific circuit design or method, but a general agreement on the need for accuracy and the use of counters is noted.

Contextual Notes

Participants have varying levels of electronics training, which may affect their understanding of the proposed solutions. The discussion includes references to external resources that may not fully address the specific needs of the project.

Who May Find This Useful

Students and hobbyists involved in automotive electronics, particularly those working on projects related to engine control and RPM measurement.

berdan
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Hi,dear engineer fellas.

Here is my query :

We are team of students who compete in international FSAE competition-that is,we are making a racing car if you will.The engine is motorcycle engine.
Our team is responsible of the different circuitry . Funny stuff is,we are all mechanical engineers :) .
Anyways:
I have to design device ,that reads the data from onboard ECU (engine control unit) tachometer.The output from the drive circuit is a
square wave with a 30% “on” (Vbat) and 70% “off” (0v) duty cycle.Every pulse means one revolution (that is changable with ECU service program ,anyway,that's what we agreed on).

What circuit can I use to decifer the RPM?The circuit we agreed on will have 9 Leds,each led simbolizes range of 1000 RPM.

http://imageshack.us/f/7/vm4s.jpg/
Anyway,being in distant past practical electronics engineer,I will try my hardest to understand what you will throw at me :) .

Thanks in advance.
 
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berdan said:
Hi,dear engineer fellas.

Here is my query :

We are team of students who compete in international FSAE competition-that is,we are making a racing car if you will.The engine is motorcycle engine.
Our team is responsible of the different circuitry . Funny stuff is,we are all mechanical engineers :) .
Anyways:
I have to design device ,that reads the data from onboard ECU (engine control unit) tachometer.The output from the drive circuit is a
square wave with a 30% “on” (Vbat) and 70% “off” (0v) duty cycle.Every pulse means one revolution (that is changable with ECU service program ,anyway,that's what we agreed on).

What circuit can I use to decifer the RPM?The circuit we agreed on will have 9 Leds,each led simbolizes range of 1000 RPM.

http://imageshack.us/f/7/vm4s.jpg/



Anyway,being in distant past practical electronics engineer,I will try my hardest to understand what you will throw at me :) .

Thanks in advance.

Since this is your schoolwork project, it is not appropriate for us to tell you how to make this circuit. You must do the bulk of the work on it.

Try starting with reading about frequency counters: http://en.wikipedia.org/wiki/Frequency_counter

And also read about decade counter ICs: http://en.wikipedia.org/wiki/4000_series#4017_decade_counter

If you have specific questions after doing that reading, please post them here. You should be able to post a block diagram of your circuit after doing that reading, however...
 
There are a number of ways to go about this. Some much more crude (simple) than others. You haven't stated any accuracy specs. Counters is a decent way to go since they will be as accurate as your timebase. Other methods are simpler and of course less accurate, but probably quite acceptable.
 
Since this is your schoolwork project, it is not appropriate for us to tell you how to make this circuit. You must do the bulk of the work on it.

It's not my schoolwork project,we are team of students who make a car.I don't get any homework credit for solving this problem..More over,our academic teachers tell us to use any information source available.

Anyway,those links do not say much to me,specialy the first one which is very generic (about the frequency counters).I tried to look more detailed circuits overthe web but not much luck.

There are a number of ways to go about this. Some much more crude (simple) than others. You haven't stated any accuracy specs. Counters is a decent way to go since they will be as accurate as your timebase. Other methods are simpler and of course less accurate, but probably quite acceptable.

Well,the only constraints for this problem that I can give,we need to measure from let's say 20 Hz to around 200 Hz (which is from 1200 RPM to 12000 RPM,because ECU onboard tachometer gives one pulse for each revolution),and ,hmm,maybe "refresh rate" sort of speak of around 500 msec (I guess that's enough time not to drive driver insane with led flickering).
Again,I am mechanical eng. student,with only rudementary electronics training and practise.
 
berdan said:
It's not my schoolwork project,we are team of students who make a car.I don't get any homework credit for solving this problem..More over,our academic teachers tell us to use any information source available.

It's not a schoolwork project, but your teachers are guiding your work? If you do not complete this project, do you still graduate?

And there is a difference between "using information sources" and asking others to draw out a schematic for you. Can you sketch how you would use the counter ICs to give you a signal that you can use to drive the LEDs? If not, you should have an EE student helping you on this project, IMO.
 
It's settled ,we going to implement it in arduino.
Thanks guys.