In photoacoustic spectroscopy, periodic modulation of light sources is one of the necessary conditions for generating photoacoustic signals. The modulation can only be realized using mechanical choppers for some light sources, such as infrared radiation sources applied in broadband photoacoustic spectroscopy. However, a commercial chopper is unsuitable for miniaturized photoacoustic spectroscopy instruments due to its large size and high cost. In this paper, we carried out the design and development of a homemade chopper and its application to carbon dioxide (CO₂) detection by photoacoustic spectroscopy. The chopper control circuit was designed based on the STM32 microcontroller technology, and a comparison experiment between the homemade chopper and the commercial chopper was conducted. The experimental results showed that the photoacoustic signals produced by both had a good consistency, verifying the feasibility and reliability of the homemade chopper, which can satisfy the application requirements of photoacoustic spectroscopy. Then, the research of photoacoustic spectroscopy for measuring CO₂ was carried out based on the homemade chopper, and the effect of humidity on the CO₂ photoacoustic signal was analyzed. It has been shown that water vapor significantly accelerates the molecular relaxation rate of CO₂, thus improving the amplitude of the photoacoustic signal of CO₂. The Allan deviation result showed that the detection sensitivity for CO₂ of the photoacoustic spectroscopy system was found to be 5 μL·L^-1 at an average time of 200 s. Compared with the CO₂ before humidification, the minimum detection limit of CO₂ was improved by a factor of 2.4 after humidification. The homemade chopper is characterized by easy integration and has reference or application value for developing high-sensitivity photoacoustic spectroscopy instruments.