Category Archives: Stellaris Launchpad

Video Explanation

I’ve made a video of the whole system explaining all of the sensors, actuators and interfaces, and some of the more advanced indicating equipment that I’m using.

A more detailed explanation of the closed loop ignition timing control is given here: http://scottsnowden.co.uk/?p=341

Closed Loop Ignition Timing Control

I have been busy over the last few weeks with various things, but have now completed most of the practical work on my project and am now at the stage of writing up the report/dissertation. I have successfully managed to achieve closed loop ignition timing control by using the Stellaris Launchpad development board to directly interface with the optical encoder on the engine and the pressure sensor charge amplifier (this replaces the AVL IndiSet 620 in my system).

ECU in black on left, angle of peak pressure and optical encoder interface on right. Connected together via serial

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High Speed ADCs and Interfacing with Texas Instruments ADS8321

I needed a high speed ADC for sampling in cylinder pressure for my ECU, and settled on trying a few from Texas Instruments. I am using an optical encoder on the engine which provides 720 pulses per revolution . If I took a sample every pulse, then at 6000 RPM (100 Hz) then I would be looking at about 720 * 100 Hz = 72,000 Samples per Second (SPS) or 72kHz ( although I realise now that I could take a sample on each edge, resulting in 1440 samples per revolution, or 144,000 SPS). That’s pretty high speed, considering most ADCs built into microcontrollers take a few microseconds to perform their conversion which results in a sampling rate of perhaps up to 50,000 SPS max for the Arduino for example. DSP chips or higher end micros probably have better performance, but for the sake of learning, I fancied trying to use an external ADC anyway.

8 MSOP breakout


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Fuel injection map and closed loop lambda feedback

I have now managed to successfully map my engine simulator for the fuel injection timings across all loads and engine speeds. I have set up a two dimensional array, of speed and throttle position, and inside each element is the time in microseconds (us) that the fuel injector should be open for. I’ve also added closed loop lambda feedback.
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Ignition Timing, Engine and Fuel Map

I have now implemented more accurate ignition timing control which is based on degrees before top dead centre rather than a fixed time period.

I’ve also implemented a simple fuel map with the ability to store new values, display the map and save the map over serial from the Arduino.

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How Torque varies with Air to Fuel Ratio

For my Stellaris Launchpad engine simulator, I wished to add a calculation of the Air to Fuel Ratio (AFR) or lambda/equivalence ratio for the current engine conditions. I did this crudely by using the throttle position, engine speed (this->s) and current fuel pulse width (this->F) as factors in calculating the AFR:

this->AFR = (0.32666 * this->s * this->throttle)/(this->F);

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