devilman96

I have a project I am working on and someone suggested that I come by here to see if you guys can help me sort some things out.

I have a 1967 Kaiser Jeep M35A2... Is a big arse military vehicle which I've been building for the past year or so. I've customized everything from the body, frame, engine, down to sound system, electronics, and... well... there isn't much which is not been hacked into, redesigned and put back together... If your interested there is a blog with the build here... but its a 21 page all day read... http://www.steelsoldiers.com/index.p...01a25b0aa34b02

Any who... I've got a pretty complicated stereo build in it as is... but I am fed up with CD's and really prefer to go the computer route which will shore up a lot and integrate a lot of unfinished work into one ordeal... I have the background for computers so installing a computer system into a vehicle is a no brainier but... If I am going to do it I want to do it ALL... If im gonna have a touch screen I might as well run all of the gauges from it, why do something half way... My hang up comes with the sensors as from what I am reading the technology is still some what in its infancy and this is where I need some help / advice...

The computer would need to get data from the following sources...

24V electrical system
12V electrical system
Oil psi 0-120psi
Engine temp 0-260 F (or C, im not we todd did)
EGT (its a multi fuel diesel, turned up a pyro is a must 0-1400 F)
IMP (boost psi) 0-25 psi
Air pressure (air brake system) 0-200 PSI
Fuel tank 1 (I have to stick w/ the current sender, what to convert this?)
Fuel tank 2 (ditto)
Speed (0 - a whopping 75 mph.. down hill with a breeze!)
tach (0-3000 RPM)
-dont NEED it but will prolly install it...
-fuel flow (0-5 gpm)
-trans temp (0-220)
-transfer case temp (0-220)
-power steering temp (0-220)

On the tach and speed... I have to install a set of sensors as is for my cruse control system, basically their inline pulse counters, magnetic) used in some of the older cars back in the day when cruse control was an option which simply screw into the manual cables form the engine and transfer case.. Im thinking those would also work for the speed and tach on the computer system but other wise im at a bit of a loss here...

If you look at the build on the truck its a huge money pit... But I am usually incredibly careful with how I spend it and want to make sure im going in the right direction when Im dropping my hard earned pennies...

Any thoughts?...

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devilman96

Ok... Lets try something more basic...

The FB has 3 pins... 5V Ground and signal... What one would do with those 3 pins is kinda missing from the manual... I am sure the designers and the guys prototyping have this sorted out but Im staring at a board with a really blank look on my face...

If I am guest'a'mating this correctly... on a temp sending unit (one wire) type, Dakota Digital or whomever's, the values might vary between manufactures but the design is the same... You would jump signal and 5V on the board... use the ground pin to run a wire to the sending unit? Oil PSI, Temp, Fuel, etc would all be like this... At that point your measuring signal via resistance and the board is using its ground as a base line for comparison???

Another thought... Voltage drop over distance? Is this an issue?

Under the air psi thread there is a resistor shown but its a two wire sending unit (one of the few as most are single wire), what's up with the resistor, what am I missing?

A posting of a graphical representation would really help the weak minded here....

2k1Toaster

The +5 and GND are just for power. They are what power all of our sensors. If you are using your own sensor, and the ground is connected (in a car all ground is connected), then the only pin you need to actually connect is the voltage input pin. That pin can take 0v to 5v. More than 5v, it blows up. Less than -0.5v it blows up. So you need 0-5v.

Now "1 wire sensors" are usually resistive sensors. That means they dont vary the voltage with the sensory input, instead they vary the resistance. So the 2 resistors you have seen are a "voltage divider". That will take the resistive output and make it a voltage output.

I will see what I can do about graphical representations but I suggest reading the wikipedia article on voltage dividers. That may help a bit with the understanding of how it works. A multimeter and trial & error will work too, but I always like to know how what I am doing works.

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mangus580

So what if you arent using it in a car, but with your own sensor? The signal has to reference a ground somehow.... Wouldnt the GND pin be for that as well?

The way I understand it, is you have:

+5 - Voltage Supply (if needed)
Sensor Input
Common GND (for both the supply and sensor)


Is this not true?

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'Burb-puter - worklog

2k1Toaster

Yes that is correct. In the car though, since most systems have a common ground through the chassis, and the brain uses that ground, they are connected that way.

The grounds need to be connected yes.

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greenman100

it is better from a noise point of view not to use the chassis ground, to use our shielded cables.

mangus580

Right.... but in the instance of the sensors that use chassis ground.... have no choice ;-)

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'Burb-puter - worklog

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