Robert Werner has developed a solar-powered tide clock using my Arduino tide prediction libraries (GitHub link) I previously described here and here. The Instructables page shows how Robert used a servo motor to actuate a pair of hands on a dial face. The red and blue hands give you the time of the next high tide and low tide, respectively.
In Robert’s tide clock, an Arduino programmed with the tide prediction library for Anchorage Alaska keeps time with a real time clock (RTC) chip. At set intervals, the Arduino checks the current time, and makes a series of tide height calculations by feeding the date and time to the tide height function in my library. By feeding a set of times in the future as well, you can generate a table of the rising and falling tide for the next few hours or days. It’s then a matter of finding the time of the next maximum tide value, and the time of the next minimum tide value (actually by checking for a change in the slope between subsequent predicted tide heights), and you end up with the times you need the clock to display.