Cruise control, anyone ever put one in?

[bravekozak]

Doctor, I am impressed. The only part of the Tracer system I am using is the combination switch. I have already finished the electrical wiring. My only problem is the speedometer cable. I phoned Mustangs, etc. today about the Ford part number for the lower cruise cable and got the wrong part per the diagram in the Ford installation guide. Which makes me want to just shorten the stock cable by three inches. Can you say "surgery". Too bad I can't use stem cells to grow the part I need.

[Chobobulous]

Lol, you had THAT much trouble pulling a harness and wiper stalk?! Me and Karl pulled an entire dealer installed cruise control from an aspire in Columbus PnP in about 20 minutes, including the bracket for the brake petal switch, ecu and vacuum resovoir things. I wish I would have had the cash or it would be hooked up to my 5th gen 626 steering wheel buttons.

It didn't appear to be a complex system at all, the ecu was zip tied to the stock ecu, 3 wires, power ground, rpm, throttle linkage and vacuum.

Anybody with a socket set and a pocketknife can (should be able to) remove a wiper stalk in about 3 minutes.

An aspire cruise control works on a festiva?! That sucks. Ive already seen two of them.

[Tim]

Tim, why didn't you use the tach feed for the speedo reed switch? essentially the same signal (though the voltage may be different).

That definitely did not occur to me at the time! Probably would have made things much easier, lol.

I would have to check my shop manuals and see if the reed switch is grounded on one end (my gut says it was, but I can't remember for sure), or if two wires run to the brain box.

Assuming it is grounded, it's highly probable that it's 12 volts. Even if it was less, a resistor could drop it to the correct voltage. From there it would literally be as easy as running a wire from the tach feed to the brain box.

However, the flip side of the coin is that both sides of the reed switch are connected directly to a microprocessor or something, making things a little more difficult. Tapping directly into the tach wire wouldn't be an option, but a workaround could easily be found. By using an independently-powered 12v relay (so as to not overload the ignition coil), connecting the tach wire to one side and the wires to the brain box to the other, this method could theoretically imitate the reed switch. Probably would be best to use a solid state relay for this purpose as I doubt a mechanical one would last long.

One thing that bugs me, though, is why they didn't just skip the reed switch altogether and tap into the tach signal? No doubt it would have been simpler and cheaper, especially on a mass-production scale.

My guess as to why hinges on this: every position on the speedometer provides unique feedback; ie the reeds open/close at a different rate dependent on speed. Whereas with the tach feed, the signal varies with RPMs, which in turn vary depending on the gear you're in. Also, one must assume the frequency of the pulses from both the reed switch and the tach signal are close enough to make the system work. Assuming they are, though, tapping into the tach signal gives rise to the following scenarios:

The difference between the tach wire/reed switch seems trivial if you're driving a stick shift; in overdrive you're going to be cruising in the same gear unless you come to a hill and downshift, at which point the cruise control is disengaged either through the pedal switches or the control stalk. After you're back in overdrive, hit resume and all is good.

But in an automatic, I can envision problems if the cruise control was tied to the tach signal. All would be fine until you get to a hill and the transmission downshifts. The cruise control would be confused by the sudden spike in RPMs and probably wig out. The same thing could occur if you were accelerating, but not in overdrive, and set the cruise control. Once the car upshifts to overdrive, the cruise control will read the drop in RPMs as a decrease in speed and accelerate the car to compromise.

I'm guessing the designers foresaw this, and since the Tracer did come in automatic variants, they chose to use the reed switch setup. It would not surprise me if, in typical Mazda fashion, the same basic setup was used in a variety of different vehicles and applications.

So I guess, after digesting all this and assuming the signals are compatible, tapping into the tach wire is the way to go. The vast majority of us drive manual transmissions, and those with autos could easily adapt to the quirks of using the tach feed, as they're pretty minor. Definitely not worth going through what I went through with the reed switch to achieve the same basic effect.

Wish I still had my Festiva so I could experiment and report my findings....



Regards,

Tim

[TorqueEffect]

That definitely did not occur to me at the time! Probably would have made things much easier, lol.

I would have to check my shop manuals and see if the reed switch is grounded on one end (my gut says it was, but I can't remember for sure), or if two wires run to the brain box.

Assuming it is grounded, it's highly probable that it's 12 volts. Even if it was less, a resistor could drop it to the correct voltage. From there it would literally be as easy as running a wire from the tach feed to the brain box.

However, the flip side of the coin is that both sides of the reed switch are connected directly to a microprocessor or something, making things a little more difficult. Tapping directly into the tach wire wouldn't be an option, but a workaround could easily be found. By using an independently-powered 12v relay (so as to not overload the ignition coil), connecting the tach wire to one side and the wires to the brain box to the other, this method could theoretically imitate the reed switch. Probably would be best to use a solid state relay for this purpose as I doubt a mechanical one would last long.

One thing that bugs me, though, is why they didn't just skip the reed switch altogether and tap into the tach signal? No doubt it would have been simpler and cheaper, especially on a mass-production scale.

My guess as to why hinges on this: every position on the speedometer provides unique feedback; ie the reeds open/close at a different rate dependent on speed. Whereas with the tach feed, the signal varies with RPMs, which in turn vary depending on the gear you're in. Also, one must assume the frequency of the pulses from both the reed switch and the tach signal are close enough to make the system work. Assuming they are, though, tapping into the tach signal gives rise to the following scenarios:

The difference between the tach wire/reed switch seems trivial if you're driving a stick shift; in overdrive you're going to be cruising in the same gear unless you come to a hill and downshift, at which point the cruise control is disengaged either through the pedal switches or the control stalk. After you're back in overdrive, hit resume and all is good.

But in an automatic, I can envision problems if the cruise control was tied to the tach signal. All would be fine until you get to a hill and the transmission downshifts. The cruise control would be confused by the sudden spike in RPMs and probably wig out. The same thing could occur if you were accelerating, but not in overdrive, and set the cruise control. Once the car upshifts to overdrive, the cruise control will read the drop in RPMs as a decrease in speed and accelerate the car to compromise.

I'm guessing the designers foresaw this, and since the Tracer did come in automatic variants, they chose to use the reed switch setup. It would not surprise me if, in typical Mazda fashion, the same basic setup was used in a variety of different vehicles and applications.

So I guess, after digesting all this and assuming the signals are compatible, tapping into the tach wire is the way to go. The vast majority of us drive manual transmissions, and those with autos could easily adapt to the quirks of using the tach feed, as they're pretty minor. Definitely not worth going through what I went through with the reed switch to achieve the same basic effect.

Wish I still had my Festiva so I could experiment and report my findings....



Regards,

Tim

Awesome, now I know what the next project on my car is going to be. Should make my trip to Baltimore later this year more bearable with cruise-control.

Time to keep an eye out for a Tracer CC system.

[crazyrog17]

What about this:

http://dx.com/p/hall-magnetic-sensor-switch-module-for-smart-car-141363

Mounted near a magnet on the inner end of the CV shaft? Epoxy the magnet on and fab a bracket to hold the sensor.

[Tim]

What about this:

http://dx.com/p/hall-magnetic-sensor-switch-module-for-smart-car-141363

Mounted near a magnet on the inner end of the CV shaft? Epoxy the magnet on and fab a bracket to hold the sensor.

If I remember right, a speedometer works off of a rotating magnet generating a force field that moves the needle more or less depending on the speed of the rotation. The reed switch would be mounted close to the magnet. As a result the reed switch closes each time the magnet passes it, at the same speed as the speedometer cable.

So if you're cruising at 70 mph, the tach would be somewhere around 3,000 RPMs. If the speedometer cable at some point between stop and full throttle turns at 3000 RPMs, then 3,000 pulses per minute should be plenty for the cruise control box (even if the car normally goes 30 mph when the speedo cable is going 3000 RPM). The same logic applies to a Hall effect sensor near an axle if the final drive ratio and the speedometer gear ratio are close/overlap enough.


Regards,

-Tim

[Tim]

UPDATE!

Found the wiring diagram for the circuit here: http://www.xsadclan.com/files/323%20...ol-circuit.gif

It's from a 323GTX, but looks exactly as I remember seeing it in the Tracer shop manual.

One side of the reed switch does indeed go to the ground, confirming my suspicions and making FestYboy's suggestion seem even more viable.

The schematic does indicate one wire going to the PCM. If I remember right it was just a 12v "on" signal, which I obtained from the power wire. Probably should double-check that against the schematic though so nothing gets fried...


-Tim

[Tim]

Awesome, now I know what the next project on my car is going to be. Should make my trip to Baltimore later this year more bearable with cruise-control.

Time to keep an eye out for a Tracer CC system.

I would hedge a bet that many Mazdas use the same essential cruise control parts, namely the brain box and control unit. The switches, wiring and control stalk can be found on virtually any late 80s/early 90s Mazda.

Might be worth your while to poke around a few Mazdas next time you're at the junkyard, Tracers are not the most common car. The brain box, if I remember right, is a gold colored box about size of a Coke can (although a lot skinnier) and is likely mounted under the dash somewhere near the driver's side.


-Tim


EDIT:


Another update!

The more I research things, the more doable plugging the tach wire into the cruise control box seems. 4th gear ratio in a manual is .88 and the speedometer gear is .91...very close to each other. So when you're cruising at 70 in 5th, the cruise control thinks you're doing 55, well within its comfort zone. If you have a 4 speed manual, the tach and speedo will be extremely close to each other in terms of signal output.

Only thing to do now is verify that the reed switch signal is 12v to ground, install the cruise control, and cross your fingers...


-Tim