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Converting Cars Displays To Digital

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Hasan

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I am a final year student of bachelor of Computer Engineering. As my final year project i am required to digitize all the displays present on the dashboard.that include the tachometer the speedometer the fuel and temprature guageand other realted items. Before converting them to digital i must firat know how they work. So can u please explain me their workin. I think that regarding tachometer when we step on the accelerator the current increases and the rpm needle moves . I wana know how the current varies.Also plz tell me how can i covert all these items to digital. Would i be requiring analog to digital converters. I fu have answers to any of my question plz reply and also plz send me if u have some useful links. Ill be refering to u from time to time as my project progresses
Thanking you in anticipation.
 

Nigel Goodwin

Super Moderator
Most Helpful Member
Hasan said:
I am a final year student of bachelor of Computer Engineering. As my final year project i am required to digitize all the displays present on the dashboard.that include the tachometer the speedometer the fuel and temprature guageand other realted items. Before converting them to digital i must firat know how they work. So can u please explain me their workin. I think that regarding tachometer when we step on the accelerator the current increases and the rpm needle moves . I wana know how the current varies.Also plz tell me how can i covert all these items to digital. Would i be requiring analog to digital converters. I fu have answers to any of my question plz reply and also plz send me if u have some useful links. Ill be refering to u from time to time as my project progresses
Thanking you in anticipation.

A lot depends on the age of the car, older cars used mechanical speedometer and tachometer displays, where a mechanical drive cable rotates a magnet (or a metal plate) inside the meter, the needle is connected to a metal plate (or a magnet) and is moved against a spring depending on the speed of the rotating part.

Your biggest problem is probably getting an electrical signal from the mechanical rotation. Car computers have been popular addons over the years, you can possibly still buy interface components?.

More modern cars may well just generate a pulse from the engine (tachometer) and gearbox (speedometer) and process them electronically. A common way of adding a tachometer is to pickup the ignition pulses, in older days coming from the points, now coupling off the input to the distributor.

The other instruments will probably be fairly easy to do, they are just crude meters fed from various transducers.
 

Hasan

New Member
Nigel Goodwin said:
Hasan said:
I am a final year student of bachelor of Computer Engineering. As my final year project i am required to digitize all the displays present on the dashboard.that include the tachometer the speedometer the fuel and temprature guageand other realted items. Before converting them to digital i must firat know how they work. So can u please explain me their workin. I think that regarding tachometer when we step on the accelerator the current increases and the rpm needle moves . I wana know how the current varies.Also plz tell me how can i covert all these items to digital. Would i be requiring analog to digital converters. I fu have answers to any of my question plz reply and also plz send me if u have some useful links. Ill be refering to u from time to time as my project progresses
Thanking you in anticipation.

A lot depends on the age of the car, older cars used mechanical speedometer and tachometer displays, where a mechanical drive cable rotates a magnet (or a metal plate) inside the meter, the needle is connected to a metal plate (or a magnet) and is moved against a spring depending on the speed of the rotating part.

Your biggest problem is probably getting an electrical signal from the mechanical rotation. Car computers have been popular addons over the years, you can possibly still buy interface components?.

More modern cars may well just generate a pulse from the engine (tachometer) and gearbox (speedometer) and process them electronically. A common way of adding a tachometer is to pickup the ignition pulses, in older days coming from the points, now coupling off the input to the distributor.

The other instruments will probably be fairly easy to do, they are just crude meters fed from various transducers.


thanx for the reply actually we are dealing with pulses as signals from the tachometer..u talked of ignition pulses to add up the tachometer would u polzzz explain that...and how should i procss them electronically what i mean to ask is that where should i get started ..should i open up my cars dashboard to work with the pulses or can i get some dummy inputs to work with..how should i count these puilses ..which microcontrller would be best.soory for soo many question but i hav to start somewhere
 

Dialtone

New Member
If you can access the coil, you can take a wire off the trigger input and count the pulses. From this, you can determine how many RPM'S (revolutions per minute), the engine is turning. To calculate this consider the following.
As each cylinder is fired, 1 pulse to the coil is required, so for example, a 4 cylinder engine will fire the coil 4 times. But all 4 cycle engines take 2 revolutions of the crank shaft for a complete cycle. Therefor each set of 4 pulses calculates to 2 rpm's. If the engine is six cylinders, then 6 pulses per 2 revolutions, 8 cylinders, 8 pulses per 2 revolutions and so on.

Where you take your signal depends on the ignition system of the automobile. If an analog tach is already present, you can use it's supply lead as your source.

Temperature sensors are fairly easy. Most operate as nothing more than tempreature sensative variable resistors. Same is true for (most) oil pressure sensors (variable resistors).

As for a speedometer input, most newer vehicles with computer control systems have a vehicle speed sensor transducer that feeds the computer for control of the automatic transmission shift points. If this is not available, another possible source of speed related info can be had from the cruise control unit if so equipped.

Dialtone
 
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