Analog to Digital Conversion too Slow

[Dave McLaughlin]

We are trying to make a set of shaft encoders for our robot, but we are having some major problems. We are using the vex line tracker set's light sensors, and have made a plate with holes in it that gives us suffiecient change in value for each state. We made an interupt to check the sensors, but the conversion from analog to digital is so slow, we can't read fast enought to get accurate values at high speeds. We have heard about using digital sensors, but wanted more input before investing.

Thanks for the help...

[tseres]

you're using the vex already...why not just buy the vex encoders and modify a drive shaft? i really dont know what to say....nothing personal or anything, i just dont think you'll get it to work properly. if you do, please let me know

Good luck!

[dtengineering]

You might want to consider using a compartor like the LM339 in a custom circuit. The comparator will compare the voltage from your sensor to a voltage that you determine (using a voltage divider... just two resistors... you could even make one a pot to make it even easier for setting up) and give you a digital output when you exceed a the set voltage.

We use an OPB706A reflective IR sensor when building mini-sumo robots. It is capable of detecting the white ring around the sumo ring against the back blackground of the ring using only a couple of resistors. One to protect the IR LED from over current, the other a "high" value to tie the output of the phototransistor to ground. We measure the voltage between the high value resistor and the OPB and find that it works well in that application... but only if the sensor is within 2mm of the surface.

Jason