Hello all,

I am a new member here so I hope no one minds if I jump in quickly and get my feet wet.

I have an Alfa 90 with a transplanted gear box that contains a 2 contact magnetic speed sensor instead of the usual 3 contact hall effect sensor originally supplied with the car.

I have read all the previous posts on how to get different sensors talking to different speedometers but could not find the answer to my question.

I am trying to check if the speedometer sensor works correctly. My question is this:

When testing the output of the sensor on an oscilloscope, does
anyone know if 12V needs to be applied to the sensor?

If so, which contact is the + supply or conversely which contact is the ground connection.

Any help would be greatly appreciated.

The part number of the sensor is 68102763


Cheers,


Marco

Problem solved!

The polarity is marked inside where the contacts are right on the plastic insulation housing.

Dooh!

Admitidly, it is not easy to see as the housing is white and does not contrast the + and - very well.

Well I applied 12VDC to the sensor and capacitivly coupled the + terminal to measure the output. Rotating the spindle with a drill, I get a sinusodal output of approximately 70 mV Pk-PK, which to me is somewhat low.

Anybody know what the expected pk-pk or rms output of these sensors are supposed to be?

Marco

just to conclude this topic so that it may help others I determined that my speedometer sensor was fine. The sensor is configured as an open collector which means that a load resistor ( 1-2K was used here) must be placed in series with the 12V supply. The speedometer pulse signal can then be measured with an oscilloscope right at (+) blade connector. My signal showed aproximately an 8V pk, which is sufficient. The signal can the be capacitively coupled to the input of the pulse amplifier by a 1uF capacitor.

i.e.

(pulse generator + terminal)--------/\/\/\/\/\/--------(+ supplyl)
|
_____ 1 uF capacitor
_____
|
|
input to amplifier or speedometer

To calibrate the signal dakota digital make a handy universal speedometer interface (SGI-5)


http://www.dakotadigital.com/

This goes for about $80.00 U.S.

Marco

wow.

I just use the tach to see how fast im going

Marco,

Thanks a lot for your in-depth research in the speedo technology!

So, what type of gearbox-sensor do you have installed in your 90? A gtv6 or a 75 box?

I have also read the old topics but I cannot recall a PROPER solution to the incombatibility of the GTV6-75 senders-speedos. Some people seemed to find some solutions but they were not readily available.

So if I am correct, with this dakota device the problem is easily solved (?). I Really do want to keep the existing speedo in my GTV6 and it is important to show the correct miles (damn those speed cameras!). And also important (maybe more) is the accuracy of the odometer.

Since you are keen on electrical/electronic stuff do you think that a DIY dakota-like device is possible to be done by you? (or anybody else who is reading and can help). Maybe an in-line rehostat type of thing...

Come on all you that you have done the LSD conversion... what have you done with the speedo problem...???

Please share!

Thaks again Marco!

Hippo58,

I have a 75 twin spark box with the two wire speedometer sensor.

The dakota device SHOULD solve all speedometer calibration issues. It simply takes a pulse train input, and depending on the switch settings on the unit will either produce more pulses per second or less.

There are some issues however that could arrise and these deal only with the amplitude of the signal. The two wire speedometer sensor produces a healthy 8V pk-pk (as measured) signal which can be directly applied to the input to the dakota digital SGI-5. If I'm not mistaken, the output of the SGI-5 is almost 12V pk-pk, which is sufficient for most speedometer inputs.

However, if the amplitude of speedometer sensor is too low (I don't know what the threshold value is for the SGI-5 unit) it is possible that you will not be able to drive sufficiently this speed converter unit.

I know from previous posts that some of the 3 wire sensors were interfaced to an amplifier unit (most likely a Schmitt triger) to provide the best signal possible for the speedometer, but this does not present a problem with the SGI-5 as it can be connected after the amplifier to perform the speed conversion.

Either way the SGI-5 is a great solution and will allow virtually any speedometer / sensor combination to be used.

So yes, in short with the dakota device the speedometer / sensor problem is easily solved.




I have ordered my SGI-5 unit, and will post some detailed instalation instructions when I have finished (hopefully successfully) the instalation.

Marco

I've ordered one of those too, the spec reads like it should do the trick.

Personally I'm quite happy knowing my speed from rpm & gear, but the wife hates it especially when I drive past a speed camera at "X" rpm & she's all "Did it go off? did it?, ah OK"

I see this device as a piece & quiet option for the passengers really

Sorry guys,but what the heck is a dakota device when its at home????


Nice info there Marco,One to put in the archive methinks....

I fitted the 75 box to my Giulietta and simply used all the 75 speedo parraphenalia to get it all working.

Barry

Sorry Marco.found the link you posted,thanks

Barry

Thanks Barry.

All,

I've just installed the SGI-5 and it works beautifully. Now my speedometer works perfectly.

My configuration consists of a three wire speedometer unit interfaced to a two wire speedometer sensor.


The hook up is fairly straight forward and simple. but is best explained with some diagrams and schematics which I will provide shortly.

The SGI-5 is a brilliant little unit that can provide calibration as well for a 3-wire speedometer sensor connecting to a two wire speedometer and naturally will calibrated a three wire speedometer connected to a three wire sensor.

As expected the SGI-5 will do the trick for any speedometer / sensor combination an Alfa user will encounter.

Details to follow.


Marco

All, here are my instruction interfacing my two wire sensor.


Interfacing Alfa Romeo Three Wire Speedometer to 2 Wire Pulse Generator
1. Turn the ignition key to OFF


2. Construct a short jumper (~5 cm) using a standard male bullet connector and female spade terminal. Connect (-) terminal from pulse generator directly to Black Gnd. terminal on the three wire interface. The three-wire terminal is located underneath the car close to the gear box.

3. Construct a second jumper with a 1.1K series resistor using a standard male bullet connector and a female spade terminal as shown in the diagram. Before crimping the female spade terminal, attach a second Signal lead as shown. Connect a standard female bullet connector to the other end of the Signal lead. (Note a 1.1k resistor was used here, but any value up to 10k should be suitable)

4. Connect the spade terminals to the speedometer pulse generator. Please pay attention to polarity. The (-) and (+) terminals are marked but are difficult to see. The diagram shows the correct orientation of the (-) and (+) terminals.

5. Connect the Gnd., +12V and signal leads. Be sure not to connect the Gnd. Lead to the (+) terminal. The Gnd. Lead from the automobile is a separate black wire with a female bullet connector.

6. Determine where the the 1-Grey, 2-Pink/Black and 3- Black leads enter the automobile (in my case directly beneath the rear seats. Note: electrical wiring colours may be different than described here.

7. Remove the rear passenger seat and lift the sound proofing insulation to uncover the the Grey, Pink/Black and Black leads.

8. Cut all three leads and make short jumper cables on all of them so that they can be inserted into SGI-5 calibration unit.

9. Insert both jumpered Pink-Black leads into the +12V terminal block of the SGI-5 unit.

10. Insert both jumpered Black leads into the Gnd. Terminal block of the SGI-5 unit.

11. Insert the jumpered grey lead coming from the speedometer pulse generator into the Sig. In. terminal of the SGI-5

12. Insert the other jumpered grey lead going to the speedometer to the the OUT1 terminal block of the SGI-5.

13. Mount the SGI-5 in a suitable location. (I mounted mine on some blue tack, which not only provides vibration isolation, but also holds the unit firmly in place with out having to drill mounting holes)

14. Cut a small hole in the insulation so that you have access to the adjustment swtiches of the SGI-5

15. Follow the calibration instructions that come with the unit to calibrate your speedometer

Note:

Make sure that electrical tape or heat shrink tubing is to insulate any exposed portions of electral wiring to not only prevent shorts circuits but to guard against oxidation. This is particularly true for the speedometer pulse generator and three wire terminal which are exposed to the elements.

As ever with Alfa's there's various different versions of this !

Mine has three wire gearbox sender (75 box) and 2 wire speedo (orig GTV6).

Using the SGI 5 was dead easy:


1/ Colouring of wiring on 3 wire sender is:
grey = signal out, black = ground, pink/black = 12v input.

2/ Colouring of wires from 2wire speedo is:
pink = 12v power, red/white = signal in.

3/ Connect three separate wires to bullet connectors, your female lead goes to signal, males to each of 12v & ground. Don't need a resistor.

4/ Run these through the rubber gromet in the floor under rear seat, where the factory wiring goes, and connect to the gearbox sender.

5/ Make up another short lead with a ring connector at one end for earthing.

6/ Connect the leads to the SGI 5 in very obvious fashion:
Both Pink from speedo and pink/black to sender both wired to the "12v" pin
Both your short new ground lead that ends in a ring and the ground from the gearbox sender to "ground" pin
Grey from sender to "in" pin
Red/white to speedo to "OUT1" pin.

7/ Mount the SGI 5 to the car, slip the ring connector for ground over one of the screws. Having the seat removed for access anyway I mounted it to the short upright metal piece under the front of the rear seat bottom so that all "drilled" metal is entirely inside the car in the dry. (With the back seat out make sure you can reach back to the SGI 5 when driving to fine tune on the road)

8/ Set the switches on the SGI 5: Set switch 1 to "on", set the other 3 to "off". Speedo will now work.

9/ Fine tune, don't worry about the host of instructions that came with the SGI 5, the above points will make it work, then just use the "fine tune" buttons to adjust the reading accurately. I just put it on axle stands and ran at lowish speeds in 5th whilst sat in garage to get it about right, then went for a drive to get it spot on at 3000 rpm. Now apparently accurate at all speeds.

Easy job done !


Also did you all know that you can adjust the speed reading at the speedo end in the standard GTV6 speedo arrangement ?
There's a small "pot" in the speedo circuitry that allows you to adjust the reading by about +- 30% with a small flat screwdriver.... I'll post a pick of exactly where to drill a hole in the top of the speedo casing to access the adjuster. This is handy if your sender or speedo still works but has got "tired" and started to under read.

a stupid question from me...but before that, my speedo now is well and truly not working (alfa 75 2.0TS) after a period of behaving erratically.

ok, back to the stupid question...

for the alfa 75, the speedo sensor/sender will actually go to an intermediate box (somebody suggested it's an amplifier) before going to the speedometer itself. i'm suspecting that most likely this intermediate box is gone.

question: can this device from dakota be used to replace this intermediate box totally? the speedo sender i have is the 3 wire type, and there are 3 wires coming from the speedometer as well.

thanks for bearing with me.

coach123

The Dakota unit has an amplifier built in. It has provisions to accept relatively low level inputs, however I don't know what that low level threshold is. The friendly people at Dakota will have that answer.

In answer to your question, YES, the Dakota unit should very well be able to replace or act as a substitute for the previous amplitier.

Unless your speedometer is faulty the SGI-5 unit should work fantastically well.

Marco