Gas detection plays an important role in many fields. Due to its advantages of high sensitivity and fast response, photoacoustic spectroscopy readily meets various gas detection needs. Based on the photoacoustic spectroscopy, this paper uses a mid-infrared LED with a central wavelength of 4300 nm instead of using a laser as the excitation light source of carbon dioxide gas. The technologies of long optical paths and acoustic resonance are exploited to develop a T-type photoacoustic cell that has an absorption cell with a gold-plated inner wall and an acoustic resonance tube coupled to its body. The first-order longitudinal resonance mode and resonance frequency of the photoacoustic cell are obtained through finite-element simulation. For a modulated output from the LED light source, a hardware drive circuit is designed. On the basis of the above work, a photoacoustic detection setup for carbon dioxide gas with an automated process is built. Experimental results reveal favorable linearity between photoacoustic signals and sample concentrations, and the noise-equivalent concentration (volume fraction) is 1.24×10^-4. The Allan deviation is used to evaluate the stability of the setup. When the average time is 200 s, the detection sensitivity of the setup is 1.8×10^-5.