[Newbie] Analog In and Phototransistor output

[JavaLaurence]

Hi electronics dudes! I wonder if you can help out a software dude who knows (too) little about your subject.

 

I bought the Analog In bricklet and some Vishay CNY70 "Reflective Optical Sensor with Transistor Output" sensors with the goal of tracking some utility meters.

 

I'd like to "hook up" the CNY70 to the Analog In by sending the +5V and GND to the emitter's two pins, and +5 to the detector side, and reading the detector's output via the Analog In.

 

I can hardly read electronics schematics, but judging by lots of example circuits (like the one attached), you electronics guys like to hang a 10k resistor between the transistor and GND.

 

I don't have an electronics lab, so I don't have a resistor 

nor a soldering gun  , so my question is: what would happen if I "forget" this resistor? 

 

I'm hoping to obtain a configuration whereby the Analog In values "live" just enough for me to track a gas/electricity meter's unit digits moving past the sensor.

[batti]

Hi,

 

in your case the phototransistor creates a current (I) flow through the resistor based on the received light. U=R*I following, the resistor R converts this current I into a voltage U. This voltage can be measured (e.g. by Analog IN Bricklet). So this resistor is necessary to create a voltage you can measure.