A single chip programmable microcomputer timer for use in car washers, air dispensing machines, pay showers, suntan salons, vacuum equipment and the like. The timer unit is designed with a 4,000 bit microcomputer chip and contains a large scale integrated (LSI) circuit comprising a central processing unit (CPU), a read only memory (ROM) for program storage and a random access memory (RAM) for general data usage. The microcomputer functions to display a friendly message to the user of the timer and to display a diagnostic message on the timer's visual display when an error is recognized by the computer. The computer will flash the visual display at a predetermined time near the end of the cycle. Two programming buttons on the timer permit the coin inventory to be examined and/or cleared in conjuction with a nonvolatile memory designed in the computer. The computer also performs other functions all of which make the timer a very useful device for its many possible applications.