microcontrollersensortemperature
I am using LM35 temperature sensor to sense temperature of surrounding. I have connected LM35 to Micro-controller through a jumper of about 20 cm. It is working fine.
Now I want to increase distance between Micro-controller and LM35 to about 10m-12m.
Is it possible? If not, how it should be done for such distance and what is maximum separable distance for LM35 and Micro-controller?
Have you 'scoped the output? The LM35 is susceptible to EMI (which you have addressed with shielded cable) and load capacitance - which may be an issue. If there is instability due to load capacitance (>50pF) you can isolate this capacitance with a series resistor. If external EMI is still an issue, an RC damper can be added. Both effects are addressed on p7 (figs 3 & 4) of the datasheeet.
For multiple sensors, an assortment of analog and digital, a simple solution would be to use an Arduino Mega with a "Mega Sensor Shield" (bottom of page) ($11-12) attached to it. DfRobot offers a Mega Sensor Shield with XBee connector on board ($18-20), which might be even more useful:
This combination allows different sensors to be plugged in, as each of the 54 digital and 16 analog IOs of the Arduino Mega are brought out to separate 3-pin headers consisting of signal, ground and Vcc (5 volts). Thus sensors which need power would also receive it from the Sensor Shield.
As the Arduino boards themselves cannot provide more than 200 to 500 mA per board, depending on the board specifics, the Sensor Shield also has a connector to accept power from a wall-wart. The Arduino is then powered off the shield, as are all the sensors.
The reason to recommend the XBee connector is that incorporating remote data logging, via a Bluetooth or WiFi XBee module, becomes easy. This is especially valuable in an environment where long cables from sensor / logger location to a computer for data visualization or long term storage bears risks of damage.
Sensor shields are also available with an SD card module on board, or connectors provided for one. This again might be useful if the data logger needs to store large volumes of data locally.
Best Answer
As always, it depends.
The longer your wires are, the more prone they are to pick up noise and hum from nearby electromagnetic sources like motors etc. You can prevent that by using shielded cables. Those made to route audio signals around are pretty good.
This however will increase the cable capacitance. If you look into the data-sheet of the LM35 you'll see that the maximum capacitance it can drive directly is around 50pF. You will easily exceed this limit with a longer shielded cable. The data-sheet also shows you what to do in this case: Connect a resistor between the sensor output and the cable.
For better performance you could convert the sensor signal into a balanced signal near the sensor and convert it back into a single-ended signal near your micro-controller. Balanced driver chips for audio would likely work well for this. If you do so, driving cables that long won't be a problem, even in noisy environments.