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December 23, 2012
about 2 years ago
My application is simple object detection (a ball passing through a chute), and I was initially very dissatisfied with the range of this circuit.
In my case, my ADC Vref was hardwired to 3.3V, and I finally figured out why this limited range to about 1 centimeter. Running at 3.3V and 5V were both limited, the former because the IR output was too dim, the latter because the top of my Vout range was clipped by the ADC VREF.
I ended up powering with 5V and adding a 10K resistor between OUT and GND. This allowed full-power IR led and cut my max Vout in half (2.5V), bringing the full range below my ADC Vref, which increased the sensing range of this unit to a full inch (2.5 CM).
In the same way, you can hook this directly to a microprocessor’s digital input by matching the value of this added OUT/GND resistor to your digital input characteristics (you’d want your IR Vout max just above the digital input’s Vmax for a low signal).
Also note that incandescent light (from standard tungsten bulbs) will throw the sensor way off as it’s much stronger than the reflected IR light. I haven’t tested sunlight, but I assume it’ll have a similar effect. I’m using my microcontroller to calibrate the analog input to account for ambient light, which should work in low/indirect indoor light.
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