I have an Arduino Uno R3 that I need to connect several (3-4) SRF05 ultrasonic sensors to, as well as a TMP36 temperature sensor, from across a room. The wire length probably needs to be about 10-20 meters, though it'll differ for each one. How can this be accomplished on a small budget?
The ultrasonic sensors should be no problem at all on 10-20m of cable. You will get glitches as a cable that long will pick up lots of interferences, such as a spike every time your fridge motor switches on. You will need to apply filtering, such as only using a value if you get the same reading 10 times in a row, within some +/- tolerance. You should also put protection diodes close to the Arduino so the spikes can never go lower than 0v or higher than 5v.
The temperature sensor is different. The interference picked up on long cables will distort the analog voltage and you can't 'filter' that. Can you put the Arduino in the same place as the thermometer and then run long wires to the digital sensors?