... concentration using a simple circuit.MQ-2 gas sensor for liquefied petroleum gas, propane, high sensitivity ... applications.Module applications:Gas leak monitoring means, suitable for liquefied petroleum gas, butane, propane, methane, ... (TTL) output, and AO analog signal output;3, TTL output valid signal is low. (When ... and 5V)AO output :0.1-0 .3 V (relative pollution), and maximum concentration voltage ...