Hydrogen sulfide (H2S) is a toxic air pollutant generated in the extraction and burning of fossil fuels and by other industrial and natural processes. Recently, there have been calls by environmental advocacy groups for new methods that citizens can use to monitor air borne H2S. In response, we have developed a method based on reaction of H2S with aqueous Cu2+ ions. The reaction is followed electrochemically using equipment that can be built by a person with limited electronics experience. We will describe the design and construction of the potentiostat and electrodes. We will also provide information on where to download the code that runs the instrument and a functional graphic user interface.