i need ideas for building a speedmeter ....

[nassus]

i want it to have 3 digits...
the input is the output of a opto-reader and the ratio i think is 1:1 but i'm not sure (i don't think the wheels are turning at the same speed as my opto-reader...because the signal comes form my shifting gear box)
i'll need every help i can get ... thanx








you have to excuse my english... :shock:

 

[DirtyLude]

A speedometer is functionaly equivelant to a tachometer. Instead of the frequency of the engine turning, you're reading the frequency of the wheels turning. The calculation to change it from frequency to speed is the only difference, but still pretty basic.

You're right, the 'output frequency' to 'wheel turns' ratio is most probably not 1:1, unfortunately it's different on most cars. The only way you will be able to find out the exact ratio is by experimentation, or if you have a shop manual with the information.

There are planty of threads on this board about tachometers. If you look them up, you'll have the basis for your speedometer.

 

[nassus]

i've done this but i'm not able to find a schematic for a digital way to display the signal, i can't just use my multimeter
and another thing, it is known that an analog tachometer uses the display to integrate the signal...so what circuit should i use? (i'm thinking to use operational amp)

 

[jbeng]

You might be able to use a frequency-to-voltage converter chip like the LM2917. Convert your freq to an appropriately scaled voltage (like .1VDC=10 miles or kilometers per hour), then display it on a multimeter or digital panel meter. Unless, of course, you're wanting to directly count the frequency digitally ...

 

[gerty]

Maybe this'll help: https://www.hobby-elec.org/e_speed2.htm
The designer of the circuit is using it for different purposes (locking doors) but it may give you a few ideas...

 

[adell]

speedo

Hi why no use a pushbike speedo. The last one I purchased would do 100kmh or 100mph. One magnet and a sensor, and different programing for all the different size wheels 8)

 

[nassus]

first of all i don't have a pushbike speedo...
say that i get one, how can i integrate that in my dashboard? and iluminate it
I've had one once and the minute i toke it apart , it didn't work anymore...so i'm not going to try that again...

 

[adell]

speedo

sorry I thought you want a speedo to use. You could illuminate it from an outside source. There are other digital speedoes available and I bought one about 14 years ago in backward New Zealand but there was no need to pull it to bits. So it suited me. You can buy cheap digital milliampmeters its the magnets and sensor that is hard to sort I guess. What is this for if its top secret, you may find more answers if you shed a little light on the subject. Good luck :wink:

 

[kybert]

This problem could be easily solved using a micro-controller.

Simply interface your sensor to a digital input, measure the spacing of the pulse gaps (duty cycle), then calculate the speed from the known (preset) wheel size.

Then set outputs connected to 3 * 7-seg display driver chips.

You could also be cleaver and add a "setup" function that allows calibration, wheel size selection, precision setting, etc...

 

[nassus]

a microcontroler could solve all my problems but unfortunately a have litle knowlege about how to programe them. and that's why i choose to build this project with clasical IC's....
i need an idea on how to quantify the input signal..i've tryed using a AND gate with 2 inputs, on one input i'll have the signal from the weels and on the other input the quantifying signal (a signal with a very precise freq.) and then a simple counter....but that did not work...because i could not set the resolution right ...
so i need more ideas...

 

[kybert]

wheel sensor (pulses)
|
schmitt trigger (to tidy up signal)
|
freq. to voltage converter (signal is now analog ramp)
|
amplify/attenuator to boost/cut signal voltage (for different wheel sizes)
|
8-bit (256 state) ADC to convert to serial data, with shift register/latch
|
3* 7-seg display driver ICs



Description:

The wheel sensor produces a pulse train whos frequency is proportional to the speed of the wheel.
Sharpen the signal by using a schmitt trigger. This will produce nice square waves at logic levels.

Now convert the pulses to a DC voltage. This will be linear voltage against speed -- as speed increases, the voltage rises.

Amplify/attenuate this voltage (via a adjustable gain op-amp based non-inverting amplifier). This will allow for calibration and adjustment for different wheel sizes.

Now this voltage represents the speed, the faster the wheel turns, the higher the voltage will be. Convert the DC voltage into a digital signal using a serial 8-bit ADC chip.

The output of the ADC will be in the range of 0-->255, and be in a serial format.

Clock the serial ADC reading into a SIPO chip, so the data appears in parrellel format at the SIPO output terminals.

Now figure out a way to convert an 8-bit word to 3* 7-seg displays (there may already be a device that can do this, im not sure)


This will allow display of speed from "0" to "255" in "1" increments.



Can you see why i prefer micro-controllers! :wink:

 

[Nigel Goodwin]

For microcontroller use there's a project by EPE magazine, you can download the software from **broken link removed**, this is the text file from that location:

PIC-Agoras by John Becker

Everyday Practical Electronics, April and May 1997
--------------------------------------------------

PIC-Agoras is a PIC16C84 microcontroller-based project
which will compute and display on an l.c.d., the distance
travelled by any wheeled object, from golf trolley to
bicycle wheel and beyond! Wheel diameters of some 3 metres
can be catered for! Multi-function display of time, distance
and speed travelled/ elapsed.

Uses a magnetic flux gate sensor. Simple to build and install.


Last updated 3rd April 1997.

 

[kybert]

Indeed Why make life complex when we have micro-controllers to do all the work for us!

 

[nassus]

i've decided to use a microcontroler but i need lots of help, i need info on what is the optimal microcontroler to use...
and now that i'm going to use a microcontroler i want to integrate more than a spedo...i want it to record the Km/h and oil presure, water temp, batery charging status, remaining fuel...and i want it all displayed on a alfanumeric display...
so enyone who is willing to help, please do so...

10X

 

[kybert]

wooooooooo....

Slow down, your getting ahead of yourself a bit!! -- Using a micro-controller isnt just picking one up and plugging in into a circuit!

The task your setting yourself is (for a beginner) very complex indeed... I suggest you slow down a bit.

To start with, you need to make some choices:

What micro is best for you?
What programming language are you going to use?
What compiler are you going to use?
What chip-programmer are you going to use?
What development enviroment are you going to use?

Possibly the simpliest to use micros i have used is the Microchip PIC (www.microchip.com). There is a very wide range of devices that can do almost any task you could imagine.

I tend to use these devices for alot of applications, coupled with MPLAB (also from microchip) or PicAnt (www.picant.com) for the development enviroment and compiler. - I program in "C" for all my embedded applications (erm, and assembly where required, but we wont get into that).


I use a old programmer that i bought about 5 years ago to program the devices.

My first suggestion would be to go to the libary or look around the internet for some projects that do simple things like flash LEDs or drive 7-segment displays.

Use a chip that is "flash programmable" as these are cheep and can be re-programmed when you make a change to your software.

Once you have mastered programming a simple application, then we can move on to the big application.

Carfull software planning will be needed for a project of this size, so dont forget to flow-chart all your code!

 

[dean_c38]

I have designed and built a digital speedometer for my car a few months ago.

It uses an opto sensor to detect rotations on the mechanical speedo dragcap, an LM2917 for freq-to-voltage conversion, an ICL7107 and finally a 3 digit 7segment display which is projected on my windshield as a HUD. Works fine and fits a 2.5 by 3 inch PCB (without the display of course).

I coulda used a micro if I wanted to but those 7107s on my junk box are very hard to resist. :lol:

 

[absolution]

i was looking at one of kyberts ideas and if using an 8 bit a/d might i suggest a CA3162, that will give you ur 8 bit resolution. use this chip in conjunction with a CA3161 and you can drive 3*7 segment displays from just 2 chips. if you do decide to go this way might i suggest also just using the 4 hz option instead of the 96 hz the a/d is capable of producing due to the fact that you may end up with a semi blurred output at the higher test rate. :twisted:

 

[nassus]

dean_c38 could you give me the schematic, i want to determine what idea is the quickest (the microchip idea or the clasic idea)...
i went on www.microchip and www.picant.com and i got scared because i don't know how to program in C or C++ ...and until i got more free time i think i'm gona do things in the old fashon way gate by gate counter by counter....

 

[dean_c38]

nassus,

I'll look for the schems on my old HD. I just had my disk replaced due to a boot failure last week and haven't extracted the old files yet. I'll post it as soon as get it.

At any rate, the circuit works by just converting the sensor pulses into a proportional voltage using an LM2917 chip then measuring the voltage with a 7107.

You can get a head start by looking at the datasheet for the LM2917 and search the threads for the circuit of an DPM using the 7107 or 7106.

 

[kybert]

If you dont have time to learn C and uProcessors, use the descrite solution.

wheel sensor (pulses)
|
schmitt trigger (to tidy up signal)
|
LM2917 - freq. to voltage converter (signal is now analog ramp)
|
amplify/attenuator to boost/cut signal voltage (for different wheel sizes)
|
CA3162 - 8-bit (256 state) ADC to convert to serial data
|
CA3161 - 3* 7-seg display driver ICs


Humm, i might have a bash at designing this if i can think of an application for it.