using an encoder without a b source

[sparkydp]

I was just wondering if anyone had successfully used the WPI encoder VI without a B source. (yes, we'd no longer be able to know direction, but for something like a shooter wheel we're only driving in one direction, that's okay). Our hopes that simply leaving the B phase unhooked leading to speed only results from the encoder VIs didn't pan out.

We're currently looking into creating an up/down counter inside periodic tasks similar to the up/down example that ships with Labview and just sampling over a given period to calculate RPM.

Just curious if anybody else had faced a similar challenge, and what they came up with. (The reason we only have one phase, is we're not using a traditional encoder, but something more like an IR tachometer, reflective spot on our shaft/wheel, with an IR LED transmitter, and a phototransistor counting pulses. In the old days, we'd write an interrupt routine to increment a counter every time the pulse was detected, and just read the counter every 40ms cycle, and divide by time elapsed)

Other ideas discussed included: generating a fake B source using some sort of transform on the A source, or mounting a second phototransistor 90 degrees off the first to get a true b source.

Open to any thoughts or suggestions,
Thanks!
-David