Electronic oscillation counting timer

An electronic timer having an oscillator formed on a single IC chip, a time constant circuit connected to said oscillator and consisting of a resistor and capacitor connected in series, a counter which counts outputs of said oscillator up to a predetermined count value and thereupon generates an output, and an output circuit for generating an output signal in response to said output from the counter, said oscillator comprising

• a first input terminal for connection with said time constant circuit,
• a second input terminal adapted to be connected to a variable resistance for supplying a reference voltage,
• a dividing resistance circuit for developing a first upper limit voltage and a lower limit voltage,
• a first upper limit comparator connected to said resistance circuit and to said first terminal for comparing a potential at said first terminal with said first upper limit voltage,
• a second upper limit comparator connected to said second terminal for comparing said potential at first terminal with said reference voltage,
• an OR-circuit for receiving outputs from said first and second upper limit comparators,
• a lower limit comparator connected to said resistance circuit and to said first terminal for comparing the potential at said first terminal with said lower limit voltage,
• a flip-flop which is set by an output from said OR-circuit and reset by an output from said lower limit comparator, and
• a transistor for discharging said capacitor in response to an output generated from said flip-flop.