speedometer cable to electronic sensor what do i need?

leezymk3

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#2
I think you have to change out your gage cluster,and get one of them display unit,($1k) and get
The speed sensor
 

hvyman

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#5
IIrc there is a clip to hold it in at the bottom of the firewall and its supposed to go behind a heat shield right there as well. Should have 3 places its held against the body iirc.
 

Satan

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#13
Not sure which tranny you have, but the 2JZ W58 tranny has a digital sending untit that can be used on the R154 (slight mod needed) and Driftmotion has a sender also. You would just use these to drive a signal to your ECU. You would need a digital speedo/display or what-not, but should be easy enough.
 

grimreaper

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#14
actually wouldnt be too difficult on paper. A small stepper/servo motor to turn the cable end on the stock gauge cluster and an 8 bit mcu would suffice quite easily. The ABS speed sensor may offer the desired input to the mcu A/D ports and your set. A clean and protected power source will be your biggest hurdle.

Been thinking about this for some time now. Never had the cluster out so not sure on the space limitations back there. You could drive the stock speedo cable from many locations though if there isnt enough room. May be a bit power hungry though..
 

1986.5supra_kid

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#17
GRIMREAPER-id pay good money for setup that works and is a digital driven speedo. plug on the back of the cluster that the cable passes throught to the gauge could be retrofitted with a stepper motor and i still have the abs sensor on my r154, its not used since i have a non abs car. If you could come up with schematic of how to build the circuit ill buy and build the board. so what is special about the power source?

The exhaust is sound. no leaks. i thought about trying to route the next cable down the firewall on the LH side of the car and across the transmission to the fitting for cable. to avoid exhaust at all costs.

like i said i drove 100 miles and it was fine. but when i parked it after this drive the heat must of saturated the plastic
 

grimreaper

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#18
the 12v from the car will have unwanted noise and substantial transients that can wipe out an IC and other items. A usb cig power plug might be a good start but dont rely on it being a clean output.
I would use a switching regulator over a linear. My last circuit used two linear regulators in series to reduce the heat dissipation from voltage drop but still ran hot. Combine the heat from the car being left in the sun, limited airflow under the dash and load and thermal runaway occurred.

The switcher will need to be protected by a TVS diode, re-settable fuse and reverse voltage protection diode. Filtering will need to be addressed both in and out of the switcher. Careful on the output side, some switchers are picky about the capacitor ESR of the TOTAL output circuit. They make ICs that combine the TVS and reverse voltage protection but through hole was hard to find when I looked. The other thing to keep in mind is that everything in front of the tvs needs to be able to handle 60V+ spikes. I would look for a TVS that clamps at 16-17v, just above the max the alt should put out when healthy. What ever your TVS lets through, will be seen by the switcher. Make sure this voltage is kept within its specs. I used this after some helpful advice from a mind with more wisdom then mine:
http://www.mouser.com/Search/ProductDetail.aspx?qs=uJpRT2lXVNXJP%252bo08dQqJQ%3d%3d

I would us an atmel 8 bit mcu for this. Tap the output of the abs sensor, HZ, into an A/D channel. Tap into the gauge to ecu speed signal, hz, to another A/D channel. A resistor in series and catcher diodes should be used to protect the A/D ports.
Use a transistor (your choosing) with flyback diodes for motor control. Control this via a digital output with a resistor in series. Make sure to match the resistor to the output pins current limits and the gain of the transistor. Also make sure the transistor can handle the motors current adequately.
My current thoughts are to use a standard 12v DC motor with enough tq to spin the original speedo cable. Havent looked into this and don’t know to much about proper ways to select a motor. Most just grab what they can from the hobby shop. Keep in mind that the motor will need to spin the cables shaft to the same rpms as stock. Havent figured out the math on that yet. The motor will need to be solidly mounted and may introduce unwanted noise and vibration at high rpms. Insulated mounts may be required.
From the tsrm, the abs sensor should output 333.3hz for every 12.4mph. Roughly 26.9hz per MPH.
Have the atmel read the abs sensor, power the dc motor via PWM and fine tune the output based on the feedback from the gauge to ecu speed signal. There are some good examples of freq counting and interrupt usage on the arduino boards. A few have also shared their digital speedo designs too. The ecu speed signal will avoid the need for a servo and a stepper wouldn’t be needed as I previously mentioned because there’s no point to holding a position. It may be easier to use a freq to volt IC to feed the speed signals to the A/D ports. Im not sure how dual freq counting will play out with the timing on the mcu.
That’s all I have so far. Just been bouncing around in the grey matter so haven’t put it to paper and calculated component values yet. Always open to critiques, not an expert by any means. Just time spent tinkering between work and class.
 

grimreaper

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#19
The power supply for the motor may need careful consideration. A lower voltage motor might be located to use the boards 5v supply but you dont want to pull to much current and drag the mcu into a brownout situation. Lots of variables to keep in mind. Have fun!
 

gtsfirefighter

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#21
The elbow off the tranny keeps breaking on my car. Those bitches aren't cheap either. That last brand new one I put in lasted 91 miles before it broke and I installed all new cables with it also. I suspect the heat off the downpipe from the gt35r is killing it.
 

Orion ZyGarian

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#22
I'm wondering about a solution for this as well. All said and done, an MPH reading shouldnt be too hard to set up, but I'd really like to still have a working odometer, and really dont want to destroy a perfectly good cluster to make space for stuff like this.

I'm tempted to just start something from scratch with a series of gauges. Again, I'd like a working odometer though, preferably a working trip odometer as well. I'm not scared of a fancy setup like an iQ3, but I dont care for how it looks personally.

How does the digidash keep track of that stuff? I'd love an all digital dash (minus a digital tach), but not crazy about converting a rare RHD piece over with the "wrong" gauge placement comparatively.
 

Enraged

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#23
if you are cooking them with heat from the downpipe, maybe you should consider using some sort of heat protection. You can get "cool tube" in various sizes to cover the speedo cable, or you could wrap your downpipe with a variety of materials. Not sure why you would continually replace the speedo cable rather that fix the cause...
 

gtsfirefighter

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#24
Replaced the first elbow with a used one and it lasted a couple of days. Was told if both cable were bad it could be putting too much tension on the cable inside the elbow. That's when I replaced everything, both cables and the elbow and wrapped that section of the downpipe and cable with a heat wrap. That elbow lasted 91 miles. I have not since bought another and will not until I resolve the heat issue so I'm not continuously buying parts.
 

1986.5supra_kid

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#29
Well it was all used. They felt good too. No needle bounce. But when they were removed and the plastic housing is melted and drooping its obvious that it was heat problem not worn out. The long part was getting cooked by the down pipe and then it would lock up and the short one would try twisting it and tear up.

Now it is routed down the intake side,by the slave,then over the transmission by the shifter to the tail housing.
 

destrux

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#32
There's a really simple solution to this.... get the marlin crawler electronic adapter that fits the trans to give the ECU a speed signal. Then buy an Autometer GPS speedometer and fit it into the stock cluster. They're pretty cool. Gearing and tire changes won't screw up your speed calibration anymore, since it actually uses satellites to read your speed.
 

Backlash2032

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#36
Can you post up some pictures of how you routed it? I'm interested to see how you did it without kinking the cable too much...
 

1986.5supra_kid

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#37
Its would be hard to get picture s of but the best I can explain it that it runs down the firewall on the intake side of the engine/trans then over the trans in the middle and into the trans. Its not kinked. After 3 speedocables that's the least of things I want to work on again
 

Backlash2032

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#38
The only places I'd be worried about would be where it comes out of thr firewall, and then where it goes into the trans. I'm honestly thinking of routing it down the transmission side of the exhaust, since I've only had issues with the short cable melting..

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