Part A: DTMF Tone Generation The DTMF tone generator | Chegg.com
Durable Tone Generators | American Time
16 Tone DTMF Generator Keypad 1234567890*#ABCD, 1750Hz tone burst, and CTCSS functionality:Amazon.com:Appstore for Android
DTMF Generator Click
Taidacent DTMF Decoder/Encoder Full Form Dial Tone Generator Dual Tone Multi-Frequency Audio Decoding Digital Display: Amazon.com: Industrial & Scientific
DIY - DTMF Tone Generator and Decoder Circuits
DTMF Decoder / Encoder
Arduino DTMF Generator
Generate DTMF Tones Only Using Arduino - Hackster.io