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Category : " DTMF Decorder circuits "

DTMF RECEIVER IC MT8870 TESTER

Catagory : DTMF Decorder circuits
The circuit is configured in balancedline mode. To reject common-mode noise signals, a balanced differential amplifier input is used. The circuit also provides an excellent bridging interface across a properly terminated telephone line. Transient protection may be achieved by splitting the input resistors and inserting zener diodes (ZD1 and ZD2) to achieve voltage clamping. This allows the transient energy to be dissipated in the resistors and diodes,and limits the maximum voltage that may appear at the inputs. [...]

DTMF Generator and Decoder

Catagory : DTMF Decorder circuits, DTMF Generator
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. [...]