DIY Digital Gauges

@Rabid Stang:

While not exactly what I'm looking for, that is helpful! Thanks! Now I know what should be possible to get out of the car.

The crucial piece of information missing from that site is the hex addresses of the PIDs (or did I miss it?). Sadly, the ECU doesn't allow you to request parameters in a textual format. You have to send a series of hex values, then the ECU responds with hex values. The problem is I don't know what hex values to send for all the various parameters. So if anyone knows the hex values for PIDs specific to Ford vehicles (odometer, fuel level, etc...), please let me know!

Due to popular demand (gofastralph), here is how you request info from OBD-II.

First, you need a chip that is able to communicate with the car's ECU over the OBD-II port. As far as I can tell, the two most popular chips for this are the ELM327 (about $35) and the STN1110 (about $10), with the STN1110 being generally regarded as faster and more stable. You build a circuit for this chip (circuit diagrams are on the datasheets for each chip) and plug it in to both the OBD-II port and either 1) a computer or 2) a microcontroller such as an Arduino. Then you send simple commands to the chip in hex format, it sends it to the ECU and gets the response, and the chip outputs hex values for the results you asked for. You can check out the wiki page I linked to in the first post for a list of general PIDs (many of which won't work). The list does not have the ford specific stuff, so in reality if you knew all the PIDs unique to ford you could get info about what gear you were in, whether or not your seatbelt was unbuckled, if the door was shut or not, and like Rabid Stang said you can do math using a combination of different values to calculate stuff such as MPG and instantaneous fuel comsumption. Noteworthy is the fact you could store all the different error codes and descriptions on a microcontroller, so when the check engine light went off you could throw the error code up onto an LCD along with the full description of what the problem is. There is so much that could be done, the only limit is your imagination.

Anyway, as an example, to request the speed of the vehicle you would send:
01 0D
01 is the mode, and 0D is the parameter you want for that particular mode. Again, see the wiki page for more examples of modes and parameters you can request. An example of the resulting output would be something like:
41 0D 78
41 is the ECU saying it is responding to a request, 0D is letting you know exactly what value it is responding to, and 78 is the actual value you wanted (in hex). 78 in hex = 120 in decimal, and the vehicle speed PID happens to be in km/h. You just convert 120 km/h to mph (unless youre weird and like metric :dunno) to get your value!

To do a full set of digital gauges, you just request a PID, convert the results into a useable format, throw it up on an LCD screen, and repeat over and over for each parameter.

Update time!

So, I got myself an Arduino Mega 2560 ($65), a 16X2 lcd screen ($15), an STN1110 ($10), and all the components to wire up the circuit for the STN1110 ($15).

The first breakthrough was that I found a list of the Ford PIDs on the internet! There was no verification that the list was correct when I found it. It was just a list on some random website. One of my friends who has access to a bunch of technical info about our cars was able to verify that many things on the list were correct. We didn't check everything, but it seems that the list I found is accurate. I will be getting a complete list of Ford specific PIDs from him soon, so that I can compare it to the list I found!

I built the circuit for the STN1110 over the course of about 2 weeks (I had to reorder parts I forgot), and many of the components are available in surface mount chips only. These chips are about the size of the presidents ear on a dime, and there are 5 connection points on some of the chips! Soldering wires directly to them is impossible, so I had to etch my own circuit boards using hydrochloric acid + hydrogen peroxide to use as an adpater for the chip so I could run wires to it. The tiny surface mount chips are soldered to the adapter board, and wires are then connected to the board so that it can be hooked in to the circuit. Its quite a pain, but it finally got finished.

Last night I was up until about 6:30 am with one of my friends coding the program for the Arduino. We gave up because it was just not working properly. When I woke up this...uh, afternoon, I realized what we were doing wrong. I forgot to tell the STN1110 to begin communicating with the car! I had originally started communication between the Arduino and the STN1110, but forgot to then tell the STN1110 to start talking with the car lol. So after that was fixed, I tested it out, and IT WORKED!!!

So now I have an lcd sticking out of this huge mess of circuits and wires over my cupholders, and it displays the RPMs and the vehicle speed in MPH. Its completely uselesss right now because the circuits go sliding around whenever I go around a corner, so the next step is to order more LCDs and make a custom instrument cluster with them.

Stay tuned, more to come as I make further progress.

Thanks FortyThree!

Here is a pic of one of the super tiny chips I had to deal with. This one has 3 connections, some other ones that were the same size had 5 connections:


A pic of the SNT1110 circuit. Its in a breadboard and looks extremely messy. I will have to make a proper circuit board for it at some point:


Another pic of the STN1110 circuit:


A pic of the lcd displaying the RPMs at idle. MPH works too, but I was just sitting in my garage. It doesn't look nearly as green in real life, its more of a greenish yellow. Also, when under the sun or other bright light source the background becomes a very deep blue and the characters become very yellow.


And finally, a pic of the entire setup. The blue looking circuit board thing is the Arduino Mega 2560. To the right is (obviously) the STN1110 circuit. To the left partly hidden behind the LCD is another breadboard just for connecting the LCD to the arduino.


I have heard of people putting iPads in their cars, but I dont know of a way to interface them to anything. Its just an iPad that is permenantly attached to your car lol. A touchscreen is definitely possible though. They require using a lot of connection points to connect them to an arduino, so you would probably need a second arduino to handle the touchscreen display. Arduinos can be wired up to talk to eachother though, so you would be able to set them up to share data or have one controll the other.

And finally, I'm using a character lcd display in these pics, but I plan to order a graphic lcd or 2 to make a digital tach and speedo. I figured that it would be better to use character lcds for the numerical readouts because they are readable in direct sunlight, the font is fairly large, you can connect 40+ of these to a single arduino, and theyre about half the price of a graphic lcd.