So now, lets talk about the history of this project...
Like every DeLorean owner, the first time they drive at night after getting the car, I was sorely disappointed. Are you seriously telling me that this car has a nice backlit HVAC panel like modern cars, but then has this crummy overhead lit instrument cluster?
Three months after I got my car it went in for winter storage, but not the cluster. I pulled out the binnacle and brought it home. Then proceeded to disassemble everything about it. I learned much about how it all works. Technology used is direct actuated air-core motors for the temp, fuel, and oil gauges. They read resistance off of each sensor. Volt meter is a D'Arsonval Movement Meter (almost the same as an air-core motor). Tachometer is an air-core motor controlled by a small analog circuit board. The speedometer is a standard cable driven mechanical (Eddy Current) unit. Odometer and trip meter attached via gearing directly to the input, and the needle driven by a rotating magnet.
History lesson - Speedometer - http://en.wikipedia.org/wiki/Speedometer
History Lesson - Air-Core Motors - http://en.wikipedia.org/wiki/Air_core_gaugeThe eddy current speedometer has been used for over a century and is still in widespread use. Until the 1980s and the appearance of electronic speedometers it was the only type commonly used.
Originally patented by a German, Otto Schulze on 7 October 1902,[2] it uses a rotating flexible cable usually driven by gearing linked to the output of the vehicle's transmission. The early Volkswagen Beetle and many motorcycles, however, use a cable driven from a front wheel.
A small permanent magnet affixed to the rotating cable interacts with a small aluminum cup (called a speedcup) attached to the shaft of the pointer on the analogue instrument. As the magnet rotates near the cup, the changing magnetic field produces eddy currents in the cup, which themselves produce another magnetic field. The effect is that the magnet exerts a torque on the cup, "dragging" it, and thus the speedometer pointer, in the direction of its rotation with no mechanical connection between them.[1]
The pointer shaft is held toward zero by a fine torsion spring. The torque on the cup increases with the speed of rotation of the magnet (which is driven by the car's transmission). Thus an increase in the speed of the car will twist the cup and speedometer pointer against the spring. The cup and pointer will turn until the torque of the eddy currents on the cup is balanced by the opposing torque of the spring, and then stop. Since the torque on the cup is exactly proportional to the car's speed, and the spring's deflection is proportional to the torque, the angle of the pointer is also proportional to the speed. At a given speed the pointer will remain motionless and pointing to the appropriate number on the speedometer's dial.
The return spring is calibrated such that a given revolution speed of the cable corresponds to a specific speed indication on the speedometer. This calibration must take into account several factors, including ratios of the tailshaft gears that drive the flexible cable, the final drive ratio in the differential, and the diameter of the driven tires.
History Lesson - D'Arsonval Movement Meter - http://www.engineersedge.com/instrum...l_movement.htmThe air core gauge consists of two independent, perpendicular coils surrounding a hollow chamber. A needle shaft protrudes into the chamber, where a permanent magnet is affixed to the shaft. When current flows through the perpendicular coils, their magnetic fields superimpose and the magnet is free to align with the combined fields.
So back in the winter of 2000/2001...A commonly used sensing mechanism used in DC ammeters, voltmeters, and ohm meters is a current-sensing device called a D’Arsonval meter movement. The D’Arsonval movement is a DC moving coil-type movement in which an electromagnetic core is suspended between the poles of a permanent magnet.
The current measured is directed through the coils of the electromagnet so that the magnetic field produced by the current opposes the field of the permanent magnet and causes rotation of the core. The core is restrained by springs so that the needle will deflect or move in proportion to the current intensity. The more current applied to the core, the stronger the opposing field, and the larger the deflection, up to the limit of the current capacity of the coil. When the current is interrupted, the opposing field collapses, and the needle is returned to zero by the restraining springs. The limit of the current that can be applied to this type movement is usually less than one milliampere.
This is when I first took apart a cluster. Upon removal of each gauge, I discovered that due to their construction there is no open space behind them for any lighting. This goes for EVERY gauge...
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When I first discovered this, I needed to figure out an alternate way to do the backlighting. I was contemplating the idea of re-molding every gauge face in clear acrylic. Lights would then illuminate at the end of it, and carefully placed scores in the plastic would light up the spots under the numbering. I was able to obtain a complete extra set of non-functional gauges I could used for experimenting and prototyping. I had done high-resolution scans of the gauges and started cleaning them up. I had posted feelers out on the DML about the project. Unfortunately by the end of 2002, it started seeming like the concept would not work well enough. It started to require significant modifications to the cluster housing, something I didn't want to do. It also was looking less and less like I would be able to retain a completely stock appearance, which was the #1 requirement. The final nail in this was the cost needed to mold new plastic. So the original project was stopped and all extra parts associated with it were boxed up for later use.
Back in 2008, I got a new idea. Unlike the 2001 project which required significant investment (plastic molding = $$$), this new idea could be a simple one-off job for my own car. The idea came to me as I was throwing out (technically recycling) a bunch of laptops where I work. Disassembling one of the laptop screens revealed a perfect piece of translucent plastic. It was thin, had a slight taper, and had formed grooves to illuminate the LCD's backlight.
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The backlight itself is a really thin cold fluorescent tube. The idea now was to remove the gauge faces, simply glue the newly cutout plastic to the metal housings of each gauge, and attach the backlight to the top of the cluster. Over the next year I collected several old LCD displays. Unfortunately by now, I started having speedometer issues. I figured as long as I would be irreversibly modifying my own cluster to do this, how about I graft an electronic speedometer on as well. So now we're ballooning again. In the junkyard I found the near-perfect replacement. From a mid-late 90's Nissan Maxima, it was 140mph in a 270º sweep, had a 6-digit ODO on top of the needle, and a 4-digit TRIP below the needle. The trip letters were a little extra spaced, and the reset arm was in a different spot, but everything else about it made it seem like a perfect match.
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I had done some experiments with it, hooked it up to its speed sensor. The speed sensor though was going to need a logic box inbetween it and the speedometer though, as it would not turn at the correct speed when attached where the angle drive would be.
While rummaging through cluster after cluster at the junkyard, an entirely new concept came to be realized. All of the new cars I had been taking apart now used completely digitally controlled clusters. Gone were the mechanical speedometers, heck gone even are the electronic speedometers with mechanical rolling numbers. Everything is 100% electronic, all contained on a single circuit board. Needles are now driven by stepper motors, no longer air-core motors. What if, just WHAT IF, I could build a completely new cluster, which would eliminate every problem known on ours. This would solve the problem of backlighting. No longer would I need to deal with light-pipes. I could just illuminate the gauges directly behind them because there would be space now. I can also inexpensively build a new housing to contain it all. I would still need new molded plastic for the front and sides of the gauges. However now I have a product that a LOT of people might be interested in, this could easily cover the investment necessary for that, along with the design and printing of the backlit decals, IC programming, circuit board design, etc. I put a feeler out for it back on DMCTalk.com, shortly before the crash. It generated enough interest that I began the necessary investments to design the project. I have sources for many of the components I'm going to need. The project is moving now, even better than expected. I'll be posting regular updates as I have them, but if a month goes by without a good update to report on then so be it.
Next up will be a detailed photo anatomy of the stock instrument cluster...
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Originally Posted by john 05141
