Question about vehicle tachometer circuitry

In summary, a team of mechanical engineering students are competing in an international car racing competition and need to design a device that reads data from an onboard tachometer. They have agreed on a circuit with 9 LEDs to represent the RPM range, and are seeking advice on what circuit to use to decipher the RPM from the square wave output of the drive circuit. The circuit needs to measure from 20 Hz to 200 Hz and have a refresh rate of around 500 msec. After researching frequency counters and decade counter ICs, they have decided to implement their solution with an Arduino. Their academic teachers have encouraged them to use various information sources for their project.
  • #1
berdan
32
0
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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  • #2
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...
 
  • #3
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.
 
  • #4
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.
 
  • #5
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.
 
  • #6
It's settled ,we going to implement it in arduino.
Thanks guys.
 

FAQ: Question about vehicle tachometer circuitry

1. What is a tachometer and what does it measure?

A tachometer is a device used to measure the rotational speed of an engine or other rotating machinery. It measures the number of revolutions per minute (RPM) of the rotating object.

2. How does a tachometer work?

A tachometer works by using a sensor or probe to detect the rotational speed of the object. The sensor sends a signal to the tachometer, which then converts it into a digital or analog reading displaying the RPM.

3. What is the purpose of a tachometer in a vehicle?

A tachometer in a vehicle is used to monitor the engine's speed and detect any potential issues. It also helps the driver maintain a consistent speed and shift gears at the appropriate time for optimal performance and fuel efficiency.

4. Can a tachometer be inaccurate?

Yes, a tachometer can be inaccurate due to factors such as a faulty sensor, incorrect wiring, or a malfunctioning tachometer unit. It is important to regularly calibrate and maintain the tachometer to ensure accurate readings.

5. Are there different types of tachometers?

Yes, there are different types of tachometers, including analog, digital, and combination (analog and digital) tachometers. They can also vary in their features and capabilities, such as the number of engine cylinders they can measure and the type of display.

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