Hello
For IR sensors you may take a look at the tutorial that i wrote on proximity sensors:
**broken link removed**
but this one is made for indoore application, for outdoor applications, i suggest you use one of those IR receiver ICs locked at 38 khz instead. In case you have one of those receiver i have a schematic that may help you.
I am sure this is the best solution for outdoor IR obstacle detection.
The schematic is quite simple if you keep in mind that:
-Rx is the IR receiver,
-there are 2 IR emmiter leds, which are switched on and off, one after the other, very fast. Each led is on one side of the sensor, so this way you can know usefull infos about your obstacle position (middle?, right?, left?) instead of just knowing weather if there is an obstacle or not.
I know it did not elaborate a lot, but am not sure you are interrested in that solution, and i don't like to waste time writing if no one is gonna read! are you interrested?