Most of the current mainstream respiratory devices for monitoring CO(2) concentration use the two-end structure combined with both reference-end and main testing-end. In this paper, we design a new single-end mainstream device for monitoring the carbon dioxide concentration that is breathed out of the human body. In this single end design, only the main testing-end will be involved. The mechanism is based on the low-cost digital processing method of blind source separation, which is used to separate the signal and then extract the reference signal. Meanwhile, in order to decrease the negative influence of device noise and the low sample precision caused by temperature drift, two steps are taken: one is wavelet denoising and the other is temperature drift compensation. These two steps are proved valid by clinical trials, thus improving the accuracy of devices.