Innovate Motorsports ST-12 - Manual (Page 22)

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As one can see, the reference pulse created would have a positive edge.
5.4.1 Making your own optical reference pulse sensor
The device to be used is a Fairchild reflective optical sensor type QRC1133. This device contains a
infrared LED to shine an infrared light beam on a mark on the balancer or flywheel and also contains a
photodiode to detect the reflected light. The device can be ordered from:
www.digikey.com Part Number QRC-1133-ND.
This device looks like this:
To use it you also need two resistors (1/4W). One resistor is 330 Ohm, the other 3.3 kOhm. The hookup
schematic to be used is this: