Haltech IG5 - Manual (Page 73)

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APPENDIX C TRIGGER INPUTS
Interfacing the IG5 with your particular trigger system is may be straightforward or
complicated. The most likely complication to arise is from the variety of trigger types still in
use. This appendix contains a lot of useful information about the different trigger types and is
essential information to anyone installing an IG5.
C.1 The Input Trigger
The IG5 ECU has been designed to trigger from a square signal that varies from a ‘low’ of
zero volts (ground) to a high of between 5 and 15 volts. The actual value of this ‘high’
voltage is not important because it is the transition from ‘low’ to ‘high’, or ‘high’ to ‘low’,
that is used to trigger the IG5 ECU. This transition is referred to as the Trigger Edge and
will be shown in the following illustrations as an upward or downward facing arrow. An
upward facing arrow would indicate that the trigger edge is the transition from low to high and
this is called a Rising Edge trigger. If the trigger edge occurs on the transition from high to
low, it will be shown as a downward facing arrow, and would be called a falling edge trigger.
See Figure C.1.
Figure C.1
In order for the IG5 to operate correctly a trigger input signal is needed for each spark event.
This signal must occur a fixed number of degrees before top dead centre (BTDC) of the
cylinder to be fired and must not change. The position of the trigger is given in crankshaft
degrees and is called Trigger Angle. In addition there should not be any variation in the
trigger angle between cylinders. The IG5 can be set by the user to have its trigger edge occur
between 50° and 100° BTDC.
In the example shown in figure C.2 the trigger occurs on a rising edge at 70° BTDC. The
falling edge could occur any time after the rising edge and has no effect on timing. In the
example shown on figure C.2 (2b) the trigger occurs at 70° BTDC but on the falling edge.