Category Archives: Programming

Computer and micro controller programming in a variety of different languages utilising many frameworks including Kohana, jQuery and CodeIgnitor

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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Getting High Tech

Just a quick one on what I’ve been up to the last few days. I now have the engine set up inside so that I don’t have to keep pushing it outside or waiting for the rain to stop. I’ve also set up an optical encoder, in-cylinder pressure sensor, and AVL IndiSet high speed data acquisition unit to capture data on a 0.25 degree crank angle resolution.

Extended exhaust manifold for indoor running

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Adding a load

More progress made today, I connected up the alternator to the engine to begin testing it under load. This was pretty successful, and the ECU all performed as expected, with only a few tweaks to the PID controller parameters to improve the AFR control. I restricted the range of fuelling down to as restricted as possible to prevent the system setting wildly large or small fuelling amounts under certain conditions. I finally managed to get the PID to maintain the AFR slightly rich within a few percent under steady state conditions.

Belt drive to alternator

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Arduino Controlled Electronic Ignition

Success! I have started and run the engine on my own electronic ignition. The problem was in the end quite simple, it turns out that the missing tooth wheel on the crank was aligned differently to what I expected. I thought that the missing tooth occurred 240 degrees after TDC, but in fact it appears to be aligned almost exactly at TDC. This meant that my spark was happening around Bottom Dead Centre, which is no use at all!

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Updates and Ignition problems

From my couple of brief tests, I’ve identified a few problems which are preventing the engine from starting up and running for more than a few seconds.

  • The ignition timing at very low speeds < 500 RPM is very erratic, and not at all on time.
  • Under heavy acceleration the ignition timing is erratic, for example when pull starting the engine
  • There are some occasional misfires
  • The ignition timing is generally not massively stable – sometimes varying as much as 10 degrees(!) Continue reading

First Test

Today was the first test of the engine with the control unit and it worked! Albeit only for a short time and a bit roughly (only had about 10 minutes to test). Initially I just needed to check that the ECU was triggering the ignition and fuel injection, and find a roughly suitable ignition angle.

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