Digital Car Gauges

[sandybeach]

Hi People - I feel like a dog chasing his tail trying to find instructions/project kits on how to build a digital temperature, oil pressure, voltmeter and tachometer gauge for a car using the existing sending units. Thanking you in advance for your assistance.

 

[stevez]

Let me propose what might be an answer but maybe not the answer to why you can't find much. Think about how many people actually want to do whatever it is that you are trying to do. Don't count the people who simply buy the car equipped that way. From the group of people who want to do it - how many will actually put time/energy into it. Many of those people haven't the time nor the resources (money, skills, etc) to approach it in DIY fashion. Some pay the money for aftermarket equipment - others just give up. What you have left are the few who want to do it and actually can do it. Now that still may not be a small number of people but divide that number by the countless variations that exist in sensors. Note also that of all the people who want to do it - only a portion would take the time to document what they've done and make it available for free.

With all of the above in mind you might be lucky enough to own a vehicle that is popular and/or common - in the sense that there are groups or clubs of people among the DIYers. Maybe those groups or clubs might help lead you to what you need.

One popular misconception is that one can do it themselves less expensively - sometimes it can be done but quite often it's not the case, especially with electronics. Even if you don't count your time (which has to be worth something) gathering all of the right stuff (presuming that kits don't exist) can be costly. The PCB, the parts, the enclosure, etc, etc.

This isn't intended to discourage you or anyone. I tend to do lots of things myself - just like many others. There is a lot of satisfaction to be had in making something yourself. I can't make a simple bookshelf for less money than I can buy one - but the one I made means more to me. I am building a small transmitter that will cost me much more than the cost of a new one - but I am doing it for the experience, the education and to prove to myself that I can do it. If those are your reasons let me encourage you to keep going. You might have to take a step back to learn more so you can apply things that are commonly available to the project of interest - beg, borrow, steal. It may not be pretty in the end and not what you'd design if you were a professional but it's yours.

Good luck.

 

[Oznog]

Dunno why stevez's gotta remind us that building your own stuff is hard- that's one of the reasons why we do it.

Having your own one-of-a-kind gauges certainly has the coolness factor. And you just learn a lot doing it.

All these are easy enough to measure. I am partial to microcontrollers myself- they are a lot to learn but by far the most powerful way to pull it off. A very complicated circuit can be done far simpler. And doing stuff like driving an LCD display can't be done without it.

 

[panic mode]

sandybeach,

what car do you have? why do you think digital is better?
you like to watch RPM numbers scrolling while you are stepping on gas?
i's better to keep your eyes on the road...
if you know what is the signal that drives analog gauges it is not
big deal to make digital one to do the same.

 

[tansis]

Getting a pic to display information on a 7 segment or small LCD display that has come directly from the sensor being observed is fairly straightforward. Newer vehicles with fuel injection have the OBDII interface that connects to the cars engine management computer to play with and kits are around that will allow you to interface a PC to this and display the data. If you are fluent in visual Basic then you can create your own software to display all the engine data in a format that you find most pleasing to the eye. Also if your budget is up to it , have a look at the growing number of small "letterbox" style LCD displays 12" wide 4" high is just the right size to go over existing instrument gauges in many cars :wink:

 

[adown]

sandybeach, The dig rpm gauge can be found by searching LM2907. Its a national chip designed just for that with schematics for an analog gauge. It will convert freq to a linear voltage, then just use the 3914 to drive led's or a 7 seg disp. If you find the press gauge please post as i am looking to do the same thing to 1500 psi for a nitrous oxide gauge.

 

[CRayD]

Auto Digital gauges

Hi all: I've been doing this for while and some of my experiances are: Generally it is easier to design your circuit around new input devices rather than try to use those are ready in the car. Digital speedo/tach is just a clocked counter feeding a multiplexed display driver. I use 74c14 Hex schmidt trigger for clock/latch/reset. The clocked counts feed a 74c925/926 4 digit driver. I only display two digits of data (99mph, 99(00) RPM. Analog intputs pressure (oil,boost,etc), temp, volt, vac. etc. are diplayed with an old intersil chip set (ca3161, ca3162). Liner input devices abound for pressure, temp.

 

[gramo]

Its not too hard to make your own gauges/devices, especailly with PIC's and the such.

You could use a single 4 Line LCD to display everything you needed too, and just throw a wire or two too different signals like the VSS (vehicle speed signal) and GPI (gear position indicator), these differ from car to car, but talk to an electrical auto mechanic, find out what drives what (signal wise) and your away!

Temperature - Probably V per Degree, Find out how much per each degree

Oil Pressure - Probably the same as above, find out max and min volts

Voltmeter - No need to even worry about that one

Tachometer gauge - If you have a coil, then you can run a signal from the -ve of the coil and count the pulses that are your spark plugs firing.

Find those bad boys out, and it will be a lot easier to help you!

 

[picbits]

Did nobody notice that this thread is over 2 years old

On an on-topic note this is what I design and build. The biggest problems are input signal conditioning and power supply consideration to make them robust enough to sit on a cars nasty spiky electrical system.

 

[gramo]

A stable power supply shouldnt be an issue, and as for sampling voltages over 5V, use voltage dividers or zener diodes to protect you I/O pins, eg

**broken link removed**

 

[gramo]

Your power supply should look a little something like this

**broken link removed**

Note that the 0.1uF is a tantalum capacitor, the 22pF are ceramic capacitors and the 10uF are electrolytic capacitors.

 

[picbits]

Dont forget you have to protect against reverse voltage, load dumps, ignition spikes, line noise etc. A standard 7805 just doesn't cut it for commercial applications. Some of the specially designed 5v regulators from National Semiconductor are more robust but you need a pretty tightly specced Low ESR cap on the output or they oscillate quite badly.