RPM Counter (tachometer) input signal

[dohnjoe]

hi

I have bought a dash panel insert (DPI) from a '96 Felicia GLX with Mono-Motronic engine management system.

I am planning to replace my existing DPI ('97 Felicia LX, carburettor) that has an electro-mechanic clock.

the only problem is that I don't know what voltage and duty cycle must have the input signal for tachometer.

I know that the donor car feeds a signal from ECU.

my guess is:

- amplitude = 5V

- shape: square wave

- duty cycle: 50^

- one pulse for each engine revolution

 

my first question is: am I right so far?

 

I can get a signal only from the ignition coil (pin 1)

but the amplitude is 200V, not square shape, and not 50% duty cycle.

 

 

my second question is: how can I adapt the signal?

[TeflonTom]

Yes that sounds about tight, it's a TTL logic output from the tacho driver in most Bosch ecu's, as far a I can remember the pulse width doesn't affect the operation of the rev counter because it reacts on the trailing edge of the signal.

there's no reason why you couldn't take the signal from the LT side of the ignition coil which would be 12v with a Hall effect type signal which would be perfectly adequate to drive the rev counter. The only thing you would need to solve then is the number of pulses per revolution, there would be 2 pulses per revolution at the ingnition coil, you can buy tacho drivers from people like luminition which are designed for that purpose which has a signal scaler/divider on a small relay sized circuit board.

[dohnjoe]

thanks for reply.

I will check at Luminition

 

in a moment of inspiration I took also the crankshaft sensor from the donor car

it fits into the gearbox bell housing.

can it help me in any way?

[TeflonTom]

Possibly yes, but i'm not sure if the carb version has the timing triggers machined onto the flywheel, so you may need to swap the flywheel for one from an fuel injected model for the sensor to work.

[dohnjoe]

do you have a photo of the flywheel with machined timing triggers?

I don't know what to look for.

[TeflonTom]

No sorry, I've never really played with any of the 1300cc engines, I expect some of the rallyists on here might have a picture though.

[adurer]

@dohnjoe

You can make your own frequency divider by 2 very cheap and easy (see schematic below). CD4027 allows input signals of up to 15V. The output signal is TTL. You can use the 7805 IC to get 5V.

[dohnjoe]

that looks an easy and elegant solution  .

do I need mandatory the 7805 to get 5V?

can't I use a resistive divider?

[adurer]

can't I use a resistive divider?

No, you can not. You need a 5V stabilized voltage.

But on second thought, due to CD4027 very low power consumption (CMOS technology) you can get away with a simple Zener circuit as shown below.

[dohnjoe]

I tested adurer's schematics in Proteus software (http://www.labcenter.com/index.cfm) and it works flawlessly 

first I created the schematics in ISIS like so:

 

then I simulated the circuit using 12V pulses as input.

the output has 5V amplitude and half of the input frequency.

 

I checked also the stability of 5V power source when battery voltage varies in 9-15V interval.

all is OK.

I even tried non-square signals as input; the circuit is unaffected.

[moatz]

@dohnjoe

 

Great work, Could you please re-post the final schematic in a clearer image, as well as a picture of the final assembled circuit if possible.

 

@adurer

 

Brilliant contribution as usual, I wonder if you still have the circuit schematic diagram that you have kindly shared before, unfortunately It's not showing anymore.

[RicardoM]

moatz

Tell us what car you have, or fill in the field in your profile.

Then explain what are you trying to do. There are a few mistakes in this topic.

[moatz]

Hi Ricardo,

Just the person I wished to discuss the idea with him. By the way I am a great fan of your brilliant posts and contributions on this forum, I always learn a lot from every single comment of yours ... Many thanks to you.

Well, I was just thinking of retrofitting an electric power assisted steering column (EPAS) from an Opel Corsa B. While doing some research on the subject, I came to know that I would need a control box to manage sending the speed and RPM signals to this system, replicating the role of the ECU in the Opel original setup, So I started to look how can I get these signals (speed and RPM) in an acceptable digital ready form that could be sent to the control box of the EPAS system.

I came to this post by coincidence while searching on the subject, and I thought this circuit might be a good solution for the first part ... (RPM) signal

Mean while I am still trying to figure out a way to get the speed signal, I was thinking of setting a crank sensor which was standard in the Felicia injection based models, However I am still not sure if the flywheel in my carb based Felicia is ready with the magnetic senders that are needed to operate this crank sensor, I hope if you please can help with a confirmation on this point or not.

 

Sorry for the long reply, I tried to explain things a little bit, and I hope to know your opinion also about the idea itself, do you think it's worthwhile or not.

Edited 2 April, 2016 by moatz

[RicardoM]

Thank you for your kind words. It is nice to hear that my posts are useful.

 

About EPAS on Felicia: before talking about input signals, my first concern would be how much current draws the motor under full load. You need to know the current 1) to assess if the charging system can cope with it and 2) to choose the right fuse for the circuit.

 

Engine speed (ES) and vehicle speed (VS) signals

In order to simulate these input signals, you need to find out exactly how they look like on the donor car. The signals vary from manufacturer to manufacturer (amplitude, frequency, pulse width, duty cycle, phase, etc.)

 

Only then I will be able to tell you what to do next. The good news is there are solutions for both signals.

Edited 3 April, 2016 by RicardoM

[moatz]

Thanks Ricardo for the clarification, Glad to hear that there might be a solution. To be honest with you I am not that knowledgeable when it comes to electronics, So please bear with me and kindly guide me to any missing information you would need me to search for, I am trying to figure out my way through all these details but I promise to be a quick and dedicated learner.
 

Meanwhile here's a summary of the information I've gathered so far. For the EPAS system it has two connectors that need inputs as follows:

1) Power Connector with 2 thick wires:

• Red     (6mm²):  +12v ignition permanent positive [50 Amp Fuse]
• Brown (6mm²):  Earth

2) Signal Connector with 5 thin wires:

• Blue/Red trace (0.5mm²):  Speed Sensor (ABS) Input  [0 - 12v Square wave]
  
  Opel Corsa has 29 notches on its ABS hub and 155/80R13 tires, Information for the generated rate of pulses per Mile is:
  
  Rim Size  Width(mm)   %    Profile(mm)   Profile(in)  Total Diameter(in)   Total Circumference(in)   Revs/Mile    ABS Pulses/Rev   ABS Pulses/Mile
        13          155          80         124             4.88                22.76                           71.5                         886                  29                       25693
   
• Red/White trace (0.5mm²):  Engine Multi-Timer Input [12v signal with 10 sec delay before being turned on; to prevent the power steering motor from being
                                               activated whilst the car is being started] 
   
• Black (0.5mm²):                  +12v ignition switched positive [5 Amp Fuse]
   
• Green (0.5mm²):                 Engine RPM Input  [0 - 12v Square wave signal , 20 - 50 % Duty Cycle , min 55 Hz , max 30 KHz
                                              @max assistance position -- the period of this square wave = 61 mS , Frequency = 16.4 Hz , RPM = 960 , Speed = 2 MPH
   
• Brown/White trace (0.5mm²): Diagnostic Output

Edited 3 April, 2016 by moatz

[RicardoM]

What Opel Corsa does the EPAS coming from? Type, year, motorization.

[moatz]

It's a 1999 Opel Corsa B, 1000 cc engine

[felicia16v]

Just buy a control box ready made they don't cost much money here. I have just wired one up in a mk2 escort and it was basically 50A in line fuse straight from battery + 2 x -ve wires and an ign on signal the control box does the rest.

It doesn't need a correct speed from a sensor just one that tells it it's above a certain speed otherwise it's far too light.

On my felicia rally car I used the skoda power rack and a citereon saxo epas pump to run it with no problems

[RicardoM]

Meanwhile here's a summary of the information I've gathered so far. For the EPAS system it has two connectors that need inputs as follows:

1) Power Connector with 2 thick wires:

• Red     (6mm²):  +12v ignition permanent positive [50 Amp Fuse]
• Brown (6mm²):  Earth

2) Signal Connector with 5 thin wires:

• Blue/Red trace (0.5mm²):  Speed Sensor (ABS) Input  [0 - 12v Square wave]

  Opel Corsa has 29 notches on its ABS hub and 155/80R13 tires, Information for the generated rate of pulses per Mile is:

  Rim Size  Width(mm)   %    Profile(mm)   Profile(in)  Total Diameter(in)   Total Circumference(in)   Revs/Mile    ABS Pulses/Rev   ABS Pulses/Mile

        13          155          80         124             4.88                22.76                           71.5                         886                  29                       25693

   

• Red/White trace (0.5mm²):  Engine Multi-Timer Input [12v signal with 10 sec delay before being turned on; to prevent the power steering motor from being

                                               activated whilst the car is being started] 

   

• Black (0.5mm²):                  +12v ignition switched positive [5 Amp Fuse]

   

• Green (0.5mm²):                 Engine RPM Input  [0 - 12v Square wave signal , 20 - 50 % Duty Cycle , min 55 Hz , max 30 KHz

                                              @max assistance position -- the period of this square wave = 61 mS , Frequency = 16.4 Hz , RPM = 960 , Speed = 2 MPH

   

• Brown/White trace (0.5mm²): Diagnostic Output

Could you share the manual you have quoted from? PM.

[moatz]

Just buy a control box ready made they don't cost much money here. I have just wired one up in a mk2 escort and it was basically 50A in line fuse straight from battery + 2 x -ve wires and an ign on signal the control box does the rest.

It doesn't need a correct speed from a sensor just one that tells it it's above a certain speed otherwise it's far too light.

On my felicia rally car I used the skoda power rack and a citereon saxo epas pump to run it with no problems

Thanks for the suggestion, I'm already aware of those ready made boxes, however its price including international delivery and customs fees + the price for the EPAS system itself here in the local market wouldn't make it a feasible solution at all. Don't judge based on what's available in the UK market, believe me It's a completely different story here.

Another reason for taking the DIY path was critics I've seen posted on many forums, detailing how unsafe it would be to just give the EPAS unit a fake signal simulating a certain fixed speed, and depend on a the driver to use this manual knob to change the level of assistance he gets.

Simply I am just trying to achieve some sort of a smart and feasible implementation as much as I can, If not a wiser decision might be to just drop the whole idea

[moatz]

Could you share the manual you have quoted from? PM.

Done, Please check your inbox

[RicardoM]

I have looked over the article you pointed and I agree that 'faking' input signals as described is indeed a primitive, dangerous 'solution'.

 

Having said that, and before diving into real electronics solutions, please let me have the big picture of the situation you are in now.

 

1. Do you have already the EPAS in your possession?
2. Did you check if it fits in place of existing steering column? Any cover modifications?
3. Do you know exactly how you will fasten it and couple it to existing steering rack?
4. Do you have access to a machining shop (lathe, mill) to fabricate various adaptation parts?

Here is a summary of EPAS for those interested.

Edited 6 April, 2016 by RicardoM

[moatz]

1. Do you have already the EPAS in your possession?

   Not yet, I am still waiting to confirm whether the needed input signals can be secured by a reasonably costing and technical solution. However both EPAS systems for Opel Corsa B & C are available at the used parts store, almost at the same price.

    

2. Did you check if it fits in place of existing steering column? Any cover modifications?

   Not yet, I don't really know if this will need major modifications or not, I can only know after I get the EPAS column.

    

3. Do you know exactly how you will fasten it and couple it to existing steering rack?

   No, Unfortunately I will just wait and see what can be done during the implementation process itself, The EPAS lower spline looks almost similar to the Felicia ones but this is just a visual remark using available online images for both columns.

    

4. Do you have access to a machining shop (lathe, mill) to fabricate various adaptation parts?

   Yes, This can be done no problem.

Edited 6 April, 2016 by moatz

[RicardoM]

OK. I have read all available, relevant documents (Opel Corsa B/C workshop manuals, TIS 2000) to cross check the information found here. Then I looked on various forums to see the feedback from Opel owners. Based on all that information, I will express my (subjective) opinion about EPS on Felicia. Here goes:

 

PRO

• very elegant solution (no messy hydraulics, no whining pump, no maintenance)
• no continuous load on engine
• allows adding power steering to Felicia with air conditioning

AGAINST

• the torque / angle sensor tends to wear out in older cars, causing jerky steering, jams (!) or even self-steering (!!). It is best to buy a second hand EPS from a newer Corsa C (2010-2011)
• it 'breaks' somehow the feedback from wheels and road
• it is more suitable for women (automatic transmission too)

Now the solutions you have been waiting for. As you already know, on Opel Corsa C the EPS wiring looks like so:

 

 

We need 3 signals: vehicle speed, engine speed, and a timer signal.

 

vehicle speed - The most reliable and accurate solution is to replicate the hardware found on Opel Corsa C. The notched disk for ABS press fitted on front left wheel hub, an ABS sensor, and an ABS signal amplifier / converter (found in relay box). When you buy the EPS from a crashed Corsa, take also an ABS sensor and the ABS signal amplifier / converter. Have a look at left front wheel hub too to measure the ABS notched disk. You will have to make a similar one and fit it to Felicia.

engine speed - The easiest solution is to build an oscillator with a fixed frequency (> 55 Hz) using half of an LM556 IC and having 12V pulses from ignition coil firing it.

timer signal - on Opel Corsa the signal (12V) comes from BCM (Body Control Module) 10 seconds after ignition on. It is easy to replicate it using the other half of LM556 IC as monostable.

[moatz]

Many thanks Ricardo for your time, clarifications and the detailed solution, I will check for the availability and the cost of the needed ABS parts and see how it goes then. Hopefully the cost for these parts and modifications would not be prohibitive.