In the examples of the MQ2 smoke detector that I have seen, the sensor is hooked up to a small board, which is hooked up to the breadboard/Arduino. Is it possible to put the MQ2 sensor directly on the breadboard, without a separate interface board?
Also, I noticed that wires needed to be soldiered to the MQ7. Do wires also need to be soldiered to the MQ2 for it to work properly?