Control Four LEDs using Keypad of a Mobile Phone through Audio Jack
The MT8870DE is a complete DTMF receiver which can be used to get the binary coded decimal corresponding to each switches of mobile phone key pad for external interfacing. If four LEDs are connected to the output pins Q4 (14), Q3 (13), Q2 (12) and Q1 (11) of MT8870DE, binary coded decimal corresponding to each switch will be displayed in the LEDs. If ‘1’ is pressed, output will be 0001. If ‘2’ is pressed, output will be 0010. If ‘3’ is pressed, output will be 0011. If ‘4’ is pressed, output will be 0100.
Click here to get the datasheet of MT8870DE. After completing the circuit, connect your mobile phone to circuit through audio jack. Type of phone is your choice. But, I used a mobile phone which have keypad as shown in the following video. Capacitors connected to the terminals of crystal oscillator should be of 22pF. Output pins Q1, Q2, Q3 and Q4 can be used to control motors, relays etc. These pins can also connected to microcontrollers for doing some large projects. Watch the following video demonstration.