A thermostat for generating control signals for a furnace, air conditioner, or the like, employs a constant frequency, periodically alternating electrical source and an oscillator incorporating an element having a thermal-sensitive electrical characteristic so the oscillator frequency varies as a function of the ambient temperature. A comparator receives the two outputs and generates a signal representative of the ambient temperature. The stable output is also provided to dividing circuits to generate a signal representative of the time that is used to interrogate a digtal memory storing a desired temperature-time period, such as a week or month. The ambient temperature signal is compared with the desired temperature signal to generate an output control signals. A display provides a read-out of time and temperature and is used along with a keyboard or the like in programming the memory.