Arduino Throttle Body Syncronization Shield

A TBS tool is rather simple in what it does; it will measure the vacuum that each cylinder is actively producing when the engine is running.  To measure vacuum with an Arduino I needed to build a shield that would contain a vacuum sensor for each cylinder on my engine (4 in my case). 

There are many vacuum sensors available from your favorite electronics parts stores.  The interesting range that I need to measure is around -33 kPa (-4.78 psi).  This is the value that should be measured on my motorcycle on a single cylinder when the engine is warm and at idle.  You should consult a service manual for the specifics for your engine.  So I picked one that measured a range between 0 kPa to -50 kPa.

Then I needed to understand how to connect this to my engine.  The service manual helps here also, but I also found many great write ups on the web.  I just needed some standard engine vacuum hose with an inner diameter of 1/8th inch which will push onto a service nipple already present on the throttle body.  This same hose will directly push onto the vacuum sensor.  I found this in bulk at my local automotive store.  I needed four hoses each with at least 3 feet length so I could put the Arduino and sensors in a safe place.

The sensor I picked required a pretty simple schematic.  It just needed three capacitors.  Further, providing that it got 5v to run on it would provide an analog voltage that represented the vacuum reading in the range of 4.6v ( at 0 kPa) to 0.1v (-50 kPa).  This is great for connecting directly to the Arduino analog input pins.

I used the free version of Eagle to design the first sensor schematic.  Eagle is a PCB design software that is commonly used by many hobbyist to design schematics and layouts for circuit boards. There are many videos and instructions on how to use Eagle, and like all moderately complex software it just takes a little time using it to become familiar with how it works. 

Then all I had to do was replicate the schematic for a single sensor four times and add the connector for pushing the shield onto the Arduino.

With the schematic complete, I switched to board layout mode and followed some other shield layouts to build an outline that would simply press onto an Arduino like all shields do.  I finished it by then placing all the parts and running all the trace lines.

Once I had the completed design and layout, I did research and found a company that did PCB prototype creation.  They accepted Eagle files directly, making it easy to upload, pick the number I wanted, and submit my order.  I then just needed to wait for my boards to be shipped to me.

My software came in two parts.  One part ran on the Arduino and collected the ADC values, filtered them, and sent the summary out the serial port.  The second part ran on the PC and listened for the data from Arduino and provided a nice UI to visualize the results.

On the Arduino, I just needed to read the ADC pins to get values, and then convert these into kPa.

    Int Sample1 = analogRead(A0);
    Int Sample2 = analogRead(A1);
    Int Sample3 = analogRead(A2);
    Int Sample3 = analogRead(A3);

Since the ADC reads as 0-1023 for 0v-5v, the sensors will read 0.1v as 50 kPa and 4.6v as 0 kPa; I can then use the following snippet of code to convert them.  Note that I am using integer math (no decimals) so I treat the actual values as the number * 1000 (thus the addition to the name with kPa1000).

    const static long kPa1000PerAdcUnit = 54; // 0.05425347 per ADC unit;
    const static long adcValueFor0Kpa = 942; // 4.6v
    long kPa1000Value = ((adcValueFor0Kpa  - adcValue) * kPa1000PerAdcUnit);

I applied some filtering, collected min and max values over a period, and a few other things with the primary goal of reducing the amount of information that gets collected.

The values can then be sent to the PC using the serial feature where the second part of the software comes in.

On the PC, I wrote a Windows WPF application in C# that listened to the serial port for data coming from the Arduino, and then had it draw four bar graphs to display the data along with useful values. I added a few buttons and serial commands between the Arduino and PC to control calibration and when to start and stop sampling and spewing all the data.

Once I thought I had everything working, it was time to attach my new tool to my motorcycle and sync the throttle bodies.

For my motorcycle this required that I lift the gas tank to get the maintenance vacuum ports. Once I had access, I just needed to spot them in all the complexity. They were pretty simple, they were little rubber nipples with a wire clip to help retain them. I had to remove these rubber covers and attach my hoses to all four of the ports.

Then I started my software, requested a calibration, started the engine and let it warm up. The PC software will update real-time graphing the results and showing the readings. I then use the idle adjustment screws to adjust the values per service manual instructions and I am done.

In the image, the red box is one of my hoses connected to the maintenance ports. The red circle shows the adjustment screw for the idle setting for that cylinder. There are four of each of these.

I have shared all the project files on GitHub so that that this project can evolve and grow with contributions from others.

Schematics for the Shield: Git Hub Eagle Files

Arduino Library for the Shield: Git Hub Arduino Shield Library

Arduino Sketch for the tool: GitHub Arduino Sketch

Windows C# Application for the tool: GitHub Windows Project