Abstract: A single-tone receiver for a device which only needs simple data which can be encoded in the seven or eight single tones which can be generated by an ordinary pushbutton telephone is provided. A telephone line interface circuit receives a signal from the telephone line. The input signal is not filtered to separate the high-frequency tones from the low-frequency tones prior to their detection. A zero crossing detector coupled to the telephone line interface detects zero crossings of a received single-tone input signal. A microprocessor coupled to the zero crossing detector counts the number of zero crossings in a period and compares the count to counts corresponding to each of the seven single-tone frequencies.