Need Help: Speedometer Signal Converter

[autofanatic31]

Hi to all. Hope you guys could help me solve my problem with regards to speedometer signal.

I just finished an engine swap. I installed a Toyota 1NZ-FE engine in to an Opel Zafira A. The Zafira gets its vehicle speed signal from the wheel sensor and the ABS computer converts it then sends it to the speedometer.

When I tried to tap on to the speedometer signal wire going to the gauge, and connected it to the speedometer that came with the Toyota engine, it reads 8x faster (if Zafira gauge is 10kph, the Toyota gauge is 80kph).

I need to have the signal adjusted, so when the Toyota engine ECU receives the speed signal, it would be correct.

I don't know much about electronics. What kind of circuit do I need? Can you provide a schematic and parts list?

I hope you guys can help. Thanks in advance.

 

[dougy83]

So you want to multiply the signal frequency by 8. Depending on the frequency range, it can be done quite simply using a microcontroller and a little code.

Do you have any information on the signal frequency, duty cycle (on/off time) and voltage characteristics?

 

[alec_t]

Are you saying you want to multiply the wheel signal pulse rate by 8 or divide it by 8

 

[dougy83]

If connected to the old gauge, which should be showing the correct reading, it's 8x higher than the new gauge. Therefore signal is to be multiplied by 8x. I had to reread it a couple of times to follow also.

 

[alec_t]

I've re-read it too, but I thought the OP was saying that the rate is 8 times too high for the ECU (not the gauge), so it needs to be divided by 8 ?? Clarification required. Division by 8 would be a lot simpler then multiplication

 

[autofanatic31]

It should be divided by 8. I only have a simple digital multimeter. Can you give some tips on how I can get the data you need, (frequency, duty cycle, voltage).

 

[alec_t]

You could use a test jig as in the attached to measure the peak voltage coming from the speed sensor, but you need also to find out the voltage which the ECU expects to receive.
A simple divide-by-8 circuit as attached may be all you need (although the sensor signal may need some filtering/shaping for clocking the IC). Its supply voltage should equal the ECU required input voltage.

 

[autofanatic31]

Thanks. I'll ask an electrician to make the circuit and test it.

 

[autofanatic31]

The electrician I asked to build the divided by 8 circuit is very busy, and haven't built it yet. I would like to try and do it myself.
I was able to get a pin-out for the CD4024B chip, but I don't know how to wire it up based on your schematics.
Hope you can give me some instructions. Assign what pins I have to use, and what to connect to them.

I got the voltage reading from the signal wire to the speedometer, its 6 volts. I just used a voltage meter. I wasn't able to use your test circuit coz my electrician wasn't able to build it also.

Thanks.

 

[alec_t]

I got the voltage reading from the signal wire to the speedometer, its 6 volts. I just used a voltage meter

If the voltage is pulsed a voltmeter alone may not give an accurate reading. You need the peak voltage; which is why I suggested the test jig. Also, you have not specified what voltage the ECU input expects. Would it be safe to drive it with a 6V signal? Does it expect a higher (peak) voltage? What power supply will you use for the divider circuit?

 

[dougy83]

The output pulse width of the binary count will high for 8 cycles and low for 8 cycles - is this going to be a problem for the ECU? Does it expect a certain pulse width? You can reduce the width to be equal to the existing pulse by putting a 4-input AND gate on the input signal and the 3 LSb of the counter. The AND gate output is the new pulse signal output.

 

[autofanatic31]

I attached pic of waveform for testing speed signal for the ECU, according to the service manual. You might be able to get the ECU input info from it.

For the supply voltage, the basic power supply I know from the car is 12v. Does it need to be a different voltage?

 

[alec_t]

You might be able to get the ECU input info from it.

From the pic (if it relates to the ECU you will be using the divider with) the speed waveform amplitude is ~13V, and its mark/space ratio isn't far off 50%; so IMO the car's 12V supply, suitably filtered, should be ok for the divider IC supply and the divider output shouldn't need pulse-width reduction using the AND gate as dougy83 suggested. Any dissenters?

 

[autofanatic31]

As I said before, I don't really know much about electronics. Please bear with me.

I don't know what's an AND gate. Will your schematic still remain the same or there will be changes? The only part I'll need is the C4024B chip, or there are other parts?

Can you guide me on the connections, based on the pin-outs.

Thanks.

 

[alec_t]

The only part I'll need is the C4024B chip, or there are other parts?

Other parts are needed for filtering the power supply and possibly the input signal. I'll sketch a circuit. If you build it it's use will be entirely at your own risk. There is a risk of damaging the ECU if 12V is too great a voltage for the speed signal input.

 

[autofanatic31]

I think the input voltage to the ecu should be 5v.

 

[autofanatic31]

I'll try to use the circuit first with the speedometer that came with the Toyota engine if it will show the correct speed. The speed signal goes to the speedometer first then, I think it filters it or something, then sends the signal to the ecu.

 

[alec_t]

I think the input voltage to the ecu should be 5v.

I think that's likely, too, but many processors these days run on 3.3V. It's possible the speedometer requires a 12V input, though (judging from the pic in post #12). Another unknown factor is the ECU input impedance.

The speed signal goes to the speedometer first then, I think it filters it or something, then sends the signal to the ecu.

So perhaps the speedo reduces the 12V signal amplitude to 5V or 3.3V or whatever the ECU expects. It's all guesswork so far. The OP needs to find out for certain what voltage levels should be applied to the ECU, e.g. is the ECU input port TTL-compatible?

 

[autofanatic31]

I checked the wiring diagram of the Toyota engine. The pic in post #12 indicates testing terminals SPD (speed signal input to ECU) and E1 (Ground).

I'll wait for your new schematic. Thanks.

 

[alec_t]

Here it is. The 12V supply input now includes protective components.
The output will be 12V pulses; so only use this circuit if you accept the risk that they may harm the ECU (but from your assurance in post #19 I think that's unlikely). The divider IC, being CMOS, can't provide much current. If the ECU needs greater current then a buffer amplifier stage will have to be added.