The tone generator (top) uses the 5589 chip and a DIP switch. You can actually hear the tones through the speaker. The bottom circuit uses the 8870 to decode a tone and display its associated number on the 7-segment LED. source

The circuit presented here enables you to detect any object capable of reflecting the IR beam and moving in front of the IR LED photodetector pair up to a distance of about 12 cm from it. The circuit uses the commonly available telephony ICs such as dial-tone generator 91214B/91215B (IC1) and DTMF decoder CM8870 (IC2) in conjunction with infrared LED (IR LED1), photodiode D1..source

Here is the DTMF (Dual Tone Multiple Frequency) application is associated with digital telephony, and provides two selected output frequencies (one high band, one low band) for a duration of 100 ms. A benchmark subroutine has been written for the COP820C/840C microcontrollers, and is outlined in detail in this application note.source

This circuit outlines two different methods of DTMF generation using a COP820C/840C microcontroller clocked with a 3.58 MHz crystal in the divide by 10 mode. This yields an instruction cycle time of 2.79 ms. The application note also provides a low true row/column decoder for the DTMF keyboard. The first method of DTMF generation provides two PWM (Pulse Width Modulation) outputs on pins G3 and G2 of the G port for 100 ms. These two PWM outputs represent the selected high band and low band frequencies respectively, and must be combined externally with an LM324 op amp or equivalent feed back circuit to produce the DTMF signal. The second method of DTMF generation uses ROM lookup tables to simulate the two selected DTMF frequencies.source