Digital display in fuel meters for cars

[jstuardo]

Hi all..<p>I want to know if there are in the market (as a separate device or already mounted in a car) a digital fuel meter.<p>At the moment, I have only seen those meters using analog displays. That kind of display is very subjective. It is not possible to know certainly how many liters are left in the tank.<p>Thanks
Jaime

[Chris Smith]

Some cars have digital everything, even in a analog format for easy viewing. <p>Some cars calculate the gallons used, galons left, miles traveled, miles to go on the tank, etc., and display all the information to a read out on the dash.

[Engineer1138]

Yes. My car has a display that shows both my average MPG and the estimated # of miles until the tank is empty based on current usage.<p>But that has nothing to do with digital gauge vs analog. The analog gauge could be every bit as accurate: it's only a display device. The problem is that it's difficult (read: expensive) to do accurate, high resolution measurements of the level of a fluid that's moving around all the time.<p>BTW: anyone know how this is usually done? My guess was that the computer calculates fuel consumption by tracking when and how much the injectors are opened along with the known value of fuel pressure.

[ecerfoglio]

It’s not easy to read a digital display in a car’s dashboard while you are driving. With an analog gauge it’s easier to get at a glance a rough idea of the amount of fuel left in the tank.<p>(An analog gauge may be a “real” needle or a bargraph, either a led array or an lcd)<p>As the tank has not a regular shape, the exact amount of fuel left is not a linear function of the float’s height. This may be an issue if you want your display to read accurately in liters (or gallons)<p>If you want a digital display to be accurate, you will have to use a microprocessor with a lookup table to compensate for the tank’s form (starting with an empty tank, add one litter (or gallon) at a time and measure the fuel’s height or the sensor’s output until you have a full tank, and build the lookup table with this data).<p>You can average many readings to compensate for movement of the fuel in the tank.

[Robert Reed]

I agree with eng 1138
The analog or digital read out has nothing to do with system accuracy. Its probably based on the same sending unit for either. Either system would be subject to the tolerance of a 'production line' rheostat. And you want resolution in liters ?
My jet ski has computerized read out for these functions and I think all functions are based on gas level at that point in time. Most of us on this forum have "engineering minds" and once we know are expected gas milage and read the gas gauge, its just quick, simple in the head arithmetic to know how much distance is left in the old tank. How hard is this? We can all calculate this in a flash, so any onboard computer could do this in its sleep. The big error in this picture would be the accuracy of the transducer (the sending unit) as is usually the case, because this is the most difficult and expensive part of these systems. I think the auto manufacturers cut corners here just as my jet ski manufacturer has done.

[Newz2000]

Is anyone else here getting flash backs of that Sienfeld episode where Kramer and the guy from the Saab dealership went on a test-drive to see how far below E the needle on the gas gauge would go before the car died?<p>I always do this; that way I know how far I can push it before making a stop at the gas station. It drives my wife nuts though when she gets in the car and the low fuel warning light is on. I tell her she can easily make it another 30 miles but she just can't handle it.

[EPA III]

Matt,<p>You been going around with my wife? She can't stand if it's below the 3/4 mark. <p>Jamie,<p>I believe I have seen dashboard computerized instrument packages that measure every concievable parameter. Even minute by minute gas mileage. I believe they have additional sensors that must be installed. <p>Go to a good auto parts store to see what is available. <p>Paul A.

[Chris Smith]

Some cars actually have flow sensors in the gas manifold and they calculate the barometric setting in the manifold as well as road speed and tank float settings to "guesstimate" the fuel used, and the fuel remaining, as well as taking the milage and dividing it by the guesstimated fuel that was consumed, and presenting it out in a MPG setting. <p>Also digital designers realized that it is harder to read some displays, so they convert the digital values into a pseudo analog display, showing a moving bar, graph, or needle. Its like loading a windows program, its easy to see the progress meter from left to right.<p>[ September 27, 2005: Message edited by: Chris Smith ]</p>

[Dean Huster]

Matt, don't try that with a diesel unless you enjoy spending lots of time at the side of the road with a tool box, a few gallons of fuel and some extra hoses trying to prime the injector pump.<p>Dean

[dacflyer]

does this help you any? i rember them frommany years ago,, don;t ask me how i rembered,,but here it is,,, http://www.dakotadigital.com
the digital people of the dashboard, for after market guages and conversions for modern and old cars,, they got a lot of neet stuff i'd like to have...

[Dean Huster]

Back in the 1970s or 1980s, Radio-Electronics (before Gernsback renamed it Electronics Now) had an article on making several small digital dashboard replacement blocks using Intersil's ADC-display driver chip pair. They has substitute modules for fuel level, temperature, voltmeter, ammeter, oil pressure, etc. and some used their own sensors vs. the OEM sensors.<p>Dean

[jollyrgr]

An analog guage is much more useful for use in measuring fuel as it gives you a "feel" for how full the tank is. <p>I had a coworker that had run out of gas several times because she trusted the "miles left" measurement on her car's computer. She had the car towed to a shop once because the computer told her she had 50 miles left on the tank. Several of us told her not to trust this. After about her third or forth time getting stranded she finally believed us. The strange thing is the analog guage would show empty but she didn't believe it!

[ecerfoglio]

When you are driving you must do just that: ** drive **.<p>If you want to drive safely, You have only a little "processing power" left (in your brains ) to attend to a digital gauge. <p>Not only does an analog gauge give you an aproximate idea of the fuel left in your tank, you also have a warning light so you don´t need to watch the gauge all the time. <p>When (If) someting red or orange lights up in the dashboard, then you pay attention. <p>Otherwise, while you are driving you are not paying much attention to the fuel gauge, the oil pressure one, thermometer, voltmeter, etc. <p>With analog gauges, you just give them a short glance periodicaly, and you just "know" that it's all OK. <p>With digital readouts you must read each one, interpret the numbers, think if it´s a normat value or a dangerous one, etc. <p>You don't have the time to do all this while driving safely.

[Robert Reed]

What I like about analog gauges is this---Most are designed to read in the middle third of the meter for acceptable operation (gas gauge included). Even in very dim light, just an occasional sweep of the eye and you know your good. For a bench voltmeter, digital readouts can be fine , for example to resolve between 20.3 volts or 20. 4 volts. For an auto oil gauge, I could care less of a reading of 38 PSI or 42 PSI.. The transducer probably isn't that accurate any how.

[mustang]

I have owned 3 Lincoln Town Cars with digital dashes. The first was is a 1981 model. The digital dash computes the miles to empty and warns at 50 miles. It computes the the mpg. All three I have owned have been very accurate. If you are willing to spend the money for a shop manual I am sure you can find out what sensors are needed. There should be plenty of information out there. Maybe a Ford mechanic could chime in here.