Haltech E8 - Manual (Page 152)

Haltech E11/E8 Instruction Manual
Smart Ignitors
Smart ignition modules are less common and control the dwell or charge time for the coils automatically.
They require a different signal from the ECU. Smart ignitors require a constant duty cycle waveform, with
the appropriate edge setup to trigger to module to fire a spark from the coils.
The duty cycle of a square wave is the ratio of its high time to its period. E.g. a 70/30 duty cycle signal is
high for 70% of its period and low for the remaining 30% regardless of frequency, as shown in the diagram
below. Constant duty can also be used on aftermarket capacitive-, inductive- or multiple-spark discharge
systems such as MSD or Jacobs.
Falling edge and Rising edge Ignition Modules
The waveform that the ignition module expects can vary depending on which edge the module fires a
spark.
• Falling Edge Triggered – Most factory ignition modules are falling edge triggered. These modules
expect a 0V input signal when the ignition system is idle. When the voltage rises to 12V, the coil is
being charged. When the input voltage returns to 0V, a spark is fired and the coil sits idle until the
input voltage to the ignition module is again raised to 12V.
•
Page: 152 Copyright © Haltech 2008
GND
+12V
70% on
Time
Voltage
30% off
Spark Edge
GND
+12V
4ms Charge
time
Time
Voltage
Spark Edge
WARNING
Never send a constant duty cycle waveform to a Dumb Ignition Module.
Using a constant duty cycle signal on a dumb ignition module will cause
the ignition coils to be damaged from overcharging. Ignition modules will
be damaged as a consequence.