Innovate Motorsports ST-12 - Manual (Page 23)

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Paint the balancer or flywheel surface flat black so as not to reflect any light. Then paint a ¼” (6 mm)
white stripe on the balancer or flywheel at 90 degrees after TDC. The edge of the stripe in rotation
direction should be at the 90 degree mark. The sensor should be mounted at TDC where the TDC mark
is when the engine is at TDC.
The device will output a pulse with the NEGATIVE edge at the 90 degree mark.
Mount the device so that it’s front edge is about 0.15” (3.8 mm) from the flywheel/balancer.
The LED shines infrared light on the flywheel balancer, but the light is absorbed by the black surface. So
the photodetector in the device is off and the CH3+ connection should be between 3 and 5V. If the
voltage is lower, replace the 3.3 kOhm resistor with a lower value, but don’t go below 1 kOhm.
When the LED shines on the white stripe, light is reflected and the photodetector is on, drawing current
through the 3.3 kOhm resistor. The voltage at the CH3+ connection should be less than 1 Volt. If the
voltage is higher, replace the 3.3 kOhm resistor with a higher value.
5.5 Measuring Frequencies, custom RPM, or speed
The ST-12 has the capability to measure frequencies on any input except input 2. It converts a frequency
signal (pulses per second) into a voltage (0..5V) to be logged in the LM-1 or a number between 0 and
1023 to be logged directly by LogWorks. This is useful for measuring custom RPM ranges, signals from
speed sensors or the frequency of MAF sensors with frequency output (as opposed to voltage output
MAF sensors).