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post #1 of 55 (permalink) Old 10-06-2013, 07:01 PM Thread Starter
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Speedometer amplifier

I have decided to understand the Milano speedometer system and I am starting this thread so that I can share knowledge with other interested Alfisti.

I no longer own a Milano. I sold my two Verdes a few years ago but I now have a platinum transaxle in my GTV6 and I want the speedometer to work. Mark Toro and others have posted some useful information on using a Dakota Digital box to convert the signal from the Milano "amplifier" box to make it compatible with the GTV6 speedometer. I bought a used amplifier and a sensor and they appeared not to work but I only had a test meter to work with and that turned out to be inadequate. So I took the plunge and bought an oscilloscope and here is what I have learned so far.

The heart of the "amplifier" is an SAF1091 chip. This chip is obsolete. You can still find them but they are expensive and that is fine with me as I am a free market guy. The spec sheet says that the inductive sensor forms part of an oscillator circuit that drops out of oscillation when a gear tooth is present at the sensor. I found it to be a little different. With the sensor connected and no tooth present the oscillator runs at about 500KHz. That is the picture on the scope which is connected to pin 7 of the chip. When a gear tooth is present at the sensor (I used the end of a chisel) the oscillator still runs but at a frequency of about 450KHz.

The output of the chip is on pin 6. With no gear tooth at the sensor pin 6 is at about zero volts. It stays at zero when the gear tooth is placed next to the sensor but it jumps to 12 volts when the gear tooth is removed and then it returns to zero. Moving the gear tooth repeatedly produces a 12 volt square wave pulse train. This is fed to the base of the transistor which provide current gain so that the pulses can drive a low impedance meter.

I am getting another "amplifier" and I will test it to verify that it works the same as the one that I have. I also bought a couple of SAF1091 chips that I will use when I get my hands on an amplifier that does not work.

I may build a jig with a gear driven by a drill motor and a stand to hold the sensor next to it. Then I will be able to see the high speed pulse train and I will be able to check out sensors and amplifiers to verify that they work and maybe troubleshoot non-working amplifiers.
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Ed Prytherch
79 Spider
85 GTV6 3L
76 Suzuki GT500

A little government and a little luck are necessary in life, but only a fool trusts either of them. - P.J. O'Rourke

Last edited by alfaparticle; 10-06-2013 at 07:10 PM.
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post #2 of 55 (permalink) Old 10-06-2013, 09:12 PM
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Subscribed. Maybe someday I'll have a functional speedo in my GTV6 with a Milano transaxle..

Carry on!

bs
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post #3 of 55 (permalink) Old 10-06-2013, 09:19 PM
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Ed

Not only will it be accurate, but it will be good for 2 seconds a lap.


Bob,
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post #4 of 55 (permalink) Old 10-07-2013, 06:25 AM
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I have this setup in my 85 GTV-6. It’s pretty simple. Here it goes. Place the sender in the gear box. Plug into Milano box under seat. Cut the 3 wire plug from old sender. 3 wires, Ground Black, +12v ING. Pink, Speedo input White or Yellow.
Box has 3 prong plug. Gnd, 12v, Speedo out. I grounded the box and ground wire
under the seat as well for noise suppression. Your done!!
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post #5 of 55 (permalink) Old 10-07-2013, 06:34 AM Thread Starter
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I have this setup in my 85 GTV-6. It’s pretty simple
It sounds like to have a late 85 GTV6. I think that they and the 86 models produce the same speedometer signal as the Milano. I think that you need a converter box if you want to use a speedometer from an earlier GTV6 with a Milano sender/amplifier.

Ed Prytherch
79 Spider
85 GTV6 3L
76 Suzuki GT500

A little government and a little luck are necessary in life, but only a fool trusts either of them. - P.J. O'Rourke
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post #6 of 55 (permalink) Old 10-07-2013, 07:16 AM Thread Starter
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Today I hooked up the amplifier and scope to the sender in my platinum transaxle and I ran the car with the wheels off the ground. The good news for me is that it is obviously working. Here is the oscilloscope trace of the out put from the amplifier that will go to the converter box. The pulse height is 12 volts and the frequency varies with wheel speed.
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Ed Prytherch
79 Spider
85 GTV6 3L
76 Suzuki GT500

A little government and a little luck are necessary in life, but only a fool trusts either of them. - P.J. O'Rourke
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post #7 of 55 (permalink) Old 10-07-2013, 07:26 AM
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No the box is the converter. The only thing in the Milano sender is the Pickup. The box is all the other stuff that was in the GTV-6 sender. I have a verde gear box in the car. If the Milano sender fits in the hole of the Old GTV-6 sender your in business.
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post #8 of 55 (permalink) Old 10-07-2013, 09:03 AM Thread Starter
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No the box is the converter. The only thing in the Milano sender is the Pickup. The box is all the other stuff that was in the GTV-6 sender.
That is true if you have a late 85/86 GTV6. The earlier cars had Alfetta type senders with just two wires going to them. That is what I have.

Ed Prytherch
79 Spider
85 GTV6 3L
76 Suzuki GT500

A little government and a little luck are necessary in life, but only a fool trusts either of them. - P.J. O'Rourke
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post #9 of 55 (permalink) Old 10-07-2013, 11:04 AM
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This is cool, wish I knew how to use an oscilloscope! I've got a Dakota Digital in my '86 GTV6 that is using a Milano sender, works great. Have another one to drop into my Verde with a platinum box in it when I get the time.

Kevin

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post #10 of 55 (permalink) Old 10-07-2013, 11:38 AM Thread Starter
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wish I knew how to use an oscilloscope
A long time ago, when I was an electrical engineering student, we split into groups of 3 or 4 for labs. One of the keys to success was to get into a group with someone who knew how to drive a 'scope.

Ed Prytherch
79 Spider
85 GTV6 3L
76 Suzuki GT500

A little government and a little luck are necessary in life, but only a fool trusts either of them. - P.J. O'Rourke
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post #11 of 55 (permalink) Old 10-08-2013, 03:46 PM Thread Starter
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I now have a test rig so that I can check out sensors and amplifiers without installing the sensor into a transmission. I plan to hook it up to my new Dakota Digital SGI-5 box tomorrow so that I can debug it on the bench before installing into the car.
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Ed Prytherch
79 Spider
85 GTV6 3L
76 Suzuki GT500

A little government and a little luck are necessary in life, but only a fool trusts either of them. - P.J. O'Rourke
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post #12 of 55 (permalink) Old 10-08-2013, 06:04 PM Thread Starter
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Dakota Digital SGI-5 hooked up

I now have the complete system except for a speedometer head wired up on the bench. I connected the SGI-5 box as follows:

PWR to the red wire of the amplifier connector and also to 12 volts.
GND to the braided wire of the amplifier connector and also to 0 volts (ground)
IN to the white wire of the amplifier connector and to the upper scope trace
OUT to the lower scope trace

I had to set the DIP switches as follows:
1 ON
2 OFF
3 does not matter
4 ON

This is a little different from mark Toro's settings.

The picture is of the input (upper) and output (lower) outputs of the SGI-5. The output waveform could be seen to compress and expand as I held down the UP and DOWN buttons respectively.

I would like to buy the connector from the Milano harness that connects to the output connector of the amplifier. Please contact me if you have one.
Thanks.
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Ed Prytherch
79 Spider
85 GTV6 3L
76 Suzuki GT500

A little government and a little luck are necessary in life, but only a fool trusts either of them. - P.J. O'Rourke
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post #13 of 55 (permalink) Old 10-08-2013, 08:02 PM
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Been watching/stalking

So the $64 question is other than doing a great job of geeking out on the tech, do you have a goal for a specific speedo to drop in or just use the old OE ones from Veglia, Jaeger or whatever other junk was on the parts shelf at Alfa any given day? I ask with a specific desire in mind to redo entire dash (more race car than purdy) and the speedo is the one tricky gauge.

The gauges I am likely going to get are for racing. So they are great and make everything but speedo. It sure would be nice to know my speed on the street since it is a dual purpose car.

Currently I run one of these at the track for laps and it helped me find out where my speedo was off for my Platinum box (40=30 and 80=65) Not something I want to leave in my car permanently though.

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post #14 of 55 (permalink) Old 10-09-2013, 05:22 AM Thread Starter
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Quote:
do you have a goal for a specific speedo to drop in or just use the old OE ones from Veglia, Jaeger or whatever other junk was on the parts shelf at Alfa any given day?
I plan to use the original one that is in my GTV6. It appears that the Dakota Digital box will interface the Milano amp to a variety of speedometers.

Ed Prytherch
79 Spider
85 GTV6 3L
76 Suzuki GT500

A little government and a little luck are necessary in life, but only a fool trusts either of them. - P.J. O'Rourke
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post #15 of 55 (permalink) Old 10-10-2013, 08:52 AM Thread Starter
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I got my Speedometer calibrated today. As was suggested in some other threads, I drove on the interstate with a GPS and found that my car goes 24 mph per 1000 rpm in 5th gear. I have 205/50-16 tires.
I then got the rear wheels off the ground with jack stands, ran it at 3000 rpm in 5th and adjusted the Dakota Digital box until my speedometer read 72 mph. To achieve that I had to use OUT3 of the Dakota box to the speedometer and the DIP switch settings were
1 ON
2 OFF
3 OFF
4 OFF

I then tested it out on the bench with my drill motor and gear to generate pulses while I monitored the pulses with the oscilloscope. It appears that the Veglia speedometer requires 100 pulses per minute per indicated mph. In other words, a pulse rate of 5500ppm will make the speedometer read 55 mph.
The pulse rate from the Jaeger amplifier box was 17500 ppm for 55 mph indicated. So the SGI-5 is reducing the pulse frequency by a factor of 3.18.

Ed Prytherch
79 Spider
85 GTV6 3L
76 Suzuki GT500

A little government and a little luck are necessary in life, but only a fool trusts either of them. - P.J. O'Rourke

Last edited by alfaparticle; 10-10-2013 at 07:42 PM. Reason: Additional information.
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