BASIC Programmable Ignition and Fuel Injection Starlet Computer

This page details the building of a very basic programmable computer for the starlet.

Theory

This is an off shoot of the igntion monitor design to measure the ignition timing of the starlet. The built in functionality of the greedy

emanage is design to measure Ignition. However timing changes as much as 5 degrees can be seen in fraction of a second.This has been explained as being caused by the MAP senor piping up pressure oscillations.

The ignition monitor has a capablility to filter changes in ignition timing to produce an average.

If you recall the first NE after a g1/g2 is 10 degree before TDC. The objective is to fire the spark BTDC.

At tooth #22 The piston will be 70 degrees BTDC. As each NE tooth represents 30 degrees.

To simply fire the spark at 30 degrees before TDC a timer is started at 70 BTDC. This timer will count down to zero and interrupt at 30 BTDC.

This can be achieved by knowing the RPM. The Timer is a 16 bit timer operating at 1mhz. One tick represent 1us. At 1000rpm there are 1000rev in 60s.

There will be 1 rev in 60ms. There are 360 degrees for one rev so 1 degree will occur in 60/360 =167us.

Therefore if I am 70btdc..and I need the spark to fire at 30 BTDC I have to make the counter count  for 70-30/40 degrees.

40 degrees is equivalent to 40 * 167us =6680us or 6680 ticks. A look up table is required which when correctly loaded with ticks can fire the spark

at the correct time for every combination of speed and boost.

Once Ignition is sorted out it is quite easy to implement batch injection of fuel. Another  map is used but it contains a value to be loaded to another timer. G2 will be used to start another time which outputs a pulse dependent on the values programmed.G1 or 12 tooth after g2 will be used to fire the injector again. g1 and g2 are 360 degrees apart. The injectors will fire every 360 degrees of crankshaft rotation.

The spark is fired every 180 degrees of crank rotation.This is equivalent to 6 ne teeth. I have rigged up a test circuit using an igniter from the toyota. I connected a battery and an MSD master blaster 2 to the system and some very hot sparks can be seen jumping across the spark plug as the distributor is rotated .

So who would believe that the ciruit contained in that perspex box can keep a toyota engine idling??????