*** UPDATE: v3.6 includes fixes to time and RTC time to display before GPS signal lock ***

*** NEXT: hook up and calibrate the outside temp sensor ***

This Arduino project uses a 20x4 LCD I installed in place of my stock speedometer to display useful information similar to this:

▀▀█ ▀▀█       12:34am
█▀▀ ▀▀█ 12.3v    NNE
█▄▄ ▄▄█ 200°F   86°F
123,456mi    Trip:123.4

-  The speed, time, and heading are all updated by the GPS module.
-  The battery voltage is taken directly from the car battery using a voltage divider to convert 0-15VDC in to 0-5VDC out.
-  The engine temperature is calculated from a 0-5VDC input from the stock ECT (engine coolant temperature) sensor. This information is also used to cycle the electric cooling fan on at 200 deg F and off at 190 deg F using a 5V coil relay controlling a heavy-duty solenoid under the hood.
-  The outside temperature is taken from a DS18B20 serial temp probe mounted at the front of the vehicle behind the bumper cover.
-  The odometer and tripmeter values are stored in the (NV)RAM of an RTC module. A momentary pushbutton reset switch is mounted in the stock location to reset the trip meter.

Portions of this program were copied from or inspired by the following:

Big LCD number font:

Overall program structure and odometer/tripmeter coding:
Kurt Schulz' Scooterputer

Tom Torfs' 8 bit converter macro:


Arduino UNO R3

SainSmart GPS Module

Antenna GPS 3V Magnetic Mount SMA

Seeed STR104B2P Protoshield

SainSmart 4-Channel 5V Relay Module

Real-time Clock (RTC)
What do you think it will take to switch over to the better screen? I'm interested in that for my vette as well as mustang. Good job btw!
<p>Hi, can you please provide specific libraries that you used? I use IDE 1.6.7 and i have errors in the compilation. Excuse my Google English .</p><p>Thanks Jiř&iacute;</p>
<p>I am currently working on a digital instrument cluster for my 1993 Mustang GT. I will be using 3 Arduinos with 3 4D Systems 3.2&quot; screens. I am using GPS for the speedo but have noticed that the speed only updates once a second. This makes the needle jump around instead of a more fluid movement. I need to see if its the screen refresh that is causing this or the GPS data. Its still a work in progess, I'll make a post once complete.</p>
<p>The 93 Mustang GT that I am making a digital instrument cluster.</p>
That's ridiculously awesome. I love it! Unfortunately, the GPS modules pretty much all update once/sec. I'm no programmer (obviously), but the only way to smooth out the display is through programming. I never bothered since I was just looking for functional. Sorry I can't really help. My old 90 GT is just sitting in the driveway now, waiting for a new home. It will be a long time before I can drive a stick again since I was in a motorcycle crash last November. My leg bones are almost completely metal now.
<p>What screen did you use?</p>

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