Help connecting an electronic speedo to a Link G4

[Adoom]

I originally posted some of this on Toyspeed.

But maybe someone on here can help.

Basically, I have a KP starlet. The drivetrain is all sorts of toyota/nissan frankenstein.

The original speedo is mechanical and it reads 20% too fast.

Recently I got a Link G4.

I'd like to use a gearbox speed sensor and connect it to the Link so I can log my speed(mainly for track days).

I got a speed sensor from an S14, it fits in my S12(CA18ET) gearbox.

I have wired the speed sensor to digital-in #4 on the link and worked out the calibration. So the Link knows how fast I am going.

BUT, the car is road legal. I have to have a working speedo! I can't use the mechanical one and the speed sensor at the same time.

So now I have a Nissan speedo(this one happens to be from an N15 pulsar).

This is where my problems start.

I can wire the speedo directly to the speed sensor and it works, but the speedo reads about double the actual speed.

Meanwhile, the Link is also still wired to the speed sensor, and showing the correct speed.

I should be able to take the signal wire from the speedo and connect it to Auxiliary output #7 on the link. Then the link can drive the speedo. The Link gives me lots of calibration options in this configuration.

But I cannot get the speedo to do anything.

Here is how it went down:

Okay, so now I have a nissan speedo. (I initially had a toyota speedo)

I wired the speed sensor directly to the speedo.

One wire to ground and the other to the signal terminal on the speedo. Then connected the positive and ground terminals on the speedo.

I used the drill to turn the speed sensor.

Using the drill, I could get the speedo needle to sweep from 0-180kmh.

(I tried the same thing on the Toyota speedo, nothing happened.)

Okay, so I moved it to the car. (It's on axle stands with no wheels on the back.)

Speed sensor is in gearbox.

Speedo connected to power and ground.

Speed sensor is connected to ground and to the signal terminal on on the speedo.

Start car and put it in 2nd gear.

Speedo goes up to 30kmh when idling. Seems too fast.

Rev engine, speedo goes up and down as expected.

Connect the digital-in wire on the Link to the signal wire from the sensor(the speedo is still attached).

Speedo says 30kmh. Link says 1654kmh.....

Forgot to calibrate the digital input(number of pulses per 100m).

NEK MINIT!

I worked out it is about 1018 pulses per 100m.

Now the speedo reads 30kmh, the link reads 14kmh(which is about right).

Rev engine, speedo goes up, Link speed reading goes up.

Put gearbox in 5th, rev to 3000rpm. Link reads 100kmh(which is about right). Speedo goes well past 180kmh.

Connect Speedo signal wire to Link Aux 7(set to speedo out).

It is set to "sweep" the needle to 200Hz on key on. This doesn't happen.

Engine running at idle. 2nd gear. Link reads 14kmh. Speedo reads 0kmh.

Aux 7 can only produce a PWM signal up to 300Hz.

What is the difference between the signal from the speed sensor and the pwm signal from Aux 7?

I don't have anything as fancy as an oscilloscope(or know how to use one) to look at the two signals.

Would the speed sensor signal be analog?

If anyone can answer this, is there a circuit I can use that will convert the pwm output from the link into the same kind of signal from the speed sensor? This would be the preferred solution.

If there are 1018 pulses per 100m. Then does that make it 2.8Hz per kmh?

If I can only produce 300Hz, doesn't that mean the Link can only make the speedo go up to 107kmh?

It works if I have the link and the speedo both attached to the speed sensor. But, the speedo reads WAAAAAAAY too fast. WOF guy won't like this.

Is there a circuit I can use that will manipulate the signal from the speed sensor to the speedo that will reduce it?

I drew some AWESOME diagrams of the two configurations.

[Adoom]

I think I can use this http://www.jaycar.co.nz/productView.asp?ID=KC5435&form=CAT2&SUBCATID=965#11

to correct the speedo when both the speedo and the link and connected to the speed sensor!

[DJZ]

I very vaguely remember when I had my car tuned they had to move the speedo from one output to another (maybe output 1 or 2?) as the one I had picked would only display up to like 90K on the speedo.

[Adoom]

I very vaguely remember when I had my car tuned they had to move the speedo from one output to another (maybe output 1 or 2?) as the one I had picked would only display up to like 90K on the speedo.

I have mine on Aux 7, which can only do pwm up to 300Hz, which would explain your speedo issue.

I do happen to have Aux 2 free(which is not limited to 300Hz), which I did not realise earlier, as it was wired to my old idle control valve and the wire is cut short....

But I should be able to at least move the needle a tiny bit if my problem was the same as yours was.