A touch pad with a simple structure to enable an electronic device to be manufactured more slimly and with low manufacturing costs. In the exhaust system, a liquid reducing agent is supplied into the exhaust gases intermittently. The PWM-to-digital circuit converts the PWM control signal into a sensing count value based on a clock signal. Described herein is a barrier that needs no splicing to be installed into a T-shaped joint space that is created by the convergence of three building structures. The systems and techniques have many uses including but not limited to secure document delivery, execution of legal documents, and electronic data interchange.