How divide / multiply low frequency pulses to create a new frequency

[teliocide]

I need to build a replacement Vehicle Speed Senor. The drive gear in my Subaru gearbox is dead and requires gearbox removal and disassembly to replace it. I intend to set up a hall effect sensor on the drive axle output.
The Engine management system requires approximately 4 pulses per axle rotation so 4 magnets are required. Sadly for some reason the magic number is not exactly 4. So i will need to divide or multiply this signal to get the speedo to read correctly.
So now I am here in search of a circuit to do the required signal frequency modification.
At this point in time i have no idea what X/÷ factor should be.

I am hoping someone can help me with a circuit.

Many thanks

 

[Tony Stewart]

How can you design without specs?

Think again.
https://www.google.ca/search?q=subaru vehicle speed sensor malfunction&ie=UTF-8&oe=UTF-8&hl=en&client=safari


To generate PLL clock X n/m requires 2 loops with counters n & m.

 

[teliocide]

You are absolutely correct.
The problem is I am not an electronics guru. I can read and build circuits but not design them.
So I must ask questions to establish the complexity of the problem.
If people assist me then I can determine if or not the solution to my problem is or not within my capacity to resolve.
My question was very general "
How divide / multiply low frequency pulses to create a new frequency
Yes i did not provide any information on the scale of the division or multiplication because at this point in time I do not know.
I was hoping to get guidance not condemnation.

 

[ronsimpson]

Interesting problem.
Do you want to do this with a micro computer or just hardware.
I think you need to pass every pulse but.....
Every 10 (some number) pulses send a double pulse. (multiply by 1.1)
Every 10 (some number) pulses skip a pulse. (divide)

 

[MikeMl]

This old post has some ideas for you...

Ultimately, the correct ratio will be m/n, where m and n are (hopefully) small integers, like m=5 and n=4.

Is the car drivable? If not, it is going to be very difficult to figure this out...

 

[alec_t]

Every 10 (some number) pulses send a double pulse. (multiply by 1.1). Every 10 (some number) pulses skip a pulse. (divide)

I was thinking along those lines, but the success or otherwise of that will depend on how the car's computer interprets the pulse train. Is it looking for regular pulse intervals, and therefore likely to reject the extra pulse, for example? If so, some means would need to be found to distribute the pulses evenly.

 

[crutschow]

Given the level of your electronics expertise and the unknown value of the frequency change needed, it might be better just to bite the bullet and buy an adjustable pulse converter for that purpose such as this one.

 

[Nigel Goodwin]

Given the level of your electronics expertise and the unknown value of the frequency change needed, it might be better just to bite the bullet and buy an adjustable pulse converter for that purpose such as this one.

Nice - now we want to know what's inside it!

 

[crutschow]

Nice - now we want to know what's inside it!

It's magic!
I would guess a microprocessor of some sort.

 

[teliocide]

Thanks to all for responding,

I got a lot of useful information from www.rjes.com Subaru Powered VW Conversions.
It was Richard that suggested 4 pulses per drive shaft rotation.
He also said that the engine management system would accept this and operate happily but the the speedometer would not show true speed.
Currently the vehicle runs fine, just the Check Engine Light continuously stares me down.
The old girl has had a hard week. 4400 km in 4 days with several hours sitting on 150 kph (legally).


As I stated I need to actually DO IT .... setup the hall effect sensor then measure the speedometer error and decide from there.
Crutschow's magic box maybe the solution if I take the lazy cowards path..... which I may....... and there is always Arduino or Picaxe.

In the end it may be a combination altering the number of magnets to match the simplest division/multiplication method.
So I pick your brains while I wait for the bits to arrive.

 

[bwilliams60]

It would take less time and effort to remove that transmission and repair it than what you are going to get into. Subaru transmissions fairly easy to Re & Re.

 

[teliocide]

Mr bwilliam60 ..... you are barking up the wrong tree. I am 4400km from home. Limited work space and only basic tools. Thanks for the negative vibes.

 

[mirel]

So I pick your brains while I wait for the bits to arrive.

Of course there is always the analogue option. Use LM2907 to convert the pickup pulses to DC voltage, via a pot connect the DC to a VCO (voltage controlled oscillator) and use the output pulses. With this circuit you can have any division of frequencies you want. You can get the basic circuits from the data sheets.

 

[Tony Stewart]

This is one block diagram for a "Fractional N Synthesizer" It could be implemented on 1 chip.... or not.

Your pulse encoder is the Master and fo = N/R * f master

 

[bwilliams60]

Mr bwilliam60 ..... you are barking up the wrong tree. I am 4400km from home. Limited work space and only basic tools. Thanks for the negative vibes.

Never meant to create negative vibes, sorry if you feel that way. I wasn't aware of your circumstances but that doesn't change my answer. I know vehicles pretty well, my boys own three Subarus so I know what you are up against. Carry on with electronic solution and good luck to you.

 

[ronsimpson]

Currently the vehicle runs fine, just the Check Engine Light continuously stares me down.

1) Get home safe!
2) Put some tape over the Check Engine Light. (to get home)
3) Know that if you Light is on then you might miss other warnings.
4) This problem will look better from home. Being many km form home (Engine Light = on) is scary.

 

[picbits]

The LM2917 approach kind of works but response times aren't brilliant and very careful selection of components is required as the accuracy drifts with temperature and we all know the ranges of temperature experienced in a car .......

I used to build and sell a device that did what you were after but due to insurance constraints I had to stop selling them. It worked by sampling an input frequency, doing some maths depending on the frequency ratio you were after then generating an output pulse train in proportion to the input. It worked exceedingly well and didn't worry about temperature drift as everything was proportional anyway.

 

[Tony Stewart]

Thanks to all for responding,

I got a lot of useful information from www.rjes.com Subaru Powered VW Conversions.
It was Richard that suggested 4 pulses per drive shaft rotation.
He also said that the engine management system would accept this and operate happily but the the speedometer would not show true speed.
Currently the vehicle runs fine, just the Check Engine Light continuously stares me down.
The old girl has had a hard week. 4400 km in 4 days with several hours sitting on 150 kph (legally).


As I stated I need to actually DO IT .... setup the hall effect sensor then measure the speedometer error and decide from there.
Crutschow's magic box maybe the solution if I take the lazy cowards path..... which I may....... and there is always Arduino or Picaxe.

In the end it may be a combination altering the number of magnets to match the simplest division/multiplication method.
So I pick your brains while I wait for the bits to arrive.

You could run a variable speed pulse generator to test your theory that it is this problem.

The list of things that can trigger the check engine light is pretty lengthy. For example, anything from a loose gas cap to a faulty fuel injector can be to blame. Some other potential culprits that can cause that malevolent glow include:

• A wet engine
• A blown gasket head
• Faulty oxygen sensors
• Worn-out spark plugs or spark plug wires
• Loose or cracked hoses and manifolds
• Sticky exhaust gas recirculation valves
• Pinched or deteriorated fuel injector O-rings
• etc etc

 

[teliocide]

Error code 33 so i know it is only the VSS

Still waiting for bits from OS
If the DIY electronics fails its only $120 for the Dakotadigital plug and play solution

 

[bwilliams60]

Have you done the tests for this code? Tell me what tests you have done and what the results were.