Haltech E6A - Manual (Page 112)

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Appendix E
Trigger Interface
Interfacing the E6A with your particular trigger system may be fairly straightforward or it may
be complicated. The variety of trigger designs available is the primary source of complication.
This appendix contains a lot of useful information about the different approaches to trigger
design and is essential information to anyone installing an E6A.
E.1 The Input Trigger
The E6A ECU has been designed to trigger from a square signal that varies from a ‘low’ of
zero volts (ground) to a voltage 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 E6A 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 E.1.
Figure E.1
In order for the E6A to operate correctly a trigger edge must be generated for each spark. This
edge must occur a fixed number of degrees before top dead centre (BTDC) 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 E6A
can be set by the user to have its trigger edge occur between 60° and 100° BTDC.
In the example shown in figure E.2a the trigger occurs on a rising edge at 70° BTDC. The
second transition, from high to low, could occur any time after the rising edge. In some
installations the second transition will coincide with 10° BTDC or TDC itself, or it could
happen as close as a few degrees after the trigger edge. This second edge will have no effect
on the correct operation of the E6A ECU. It is only the position of the triggering edge that is
of importance.