MT8870 module is a low-power device DTMF decoder. It is a complete DTMF receiver integrating both the band-split filter and digital decoding functions. This module is suitable for modem interfaces, mobile radios, and other DTMF-related applications. DTMF (Dual Tone Multi-Frequency) signaling is used for telecommunication signaling over the telephone lines in the voice frequency band between communication devices (telephone, mobile).
DTMF is commonly found in tone-based dial pad devices such as mobile phones or telephone dial pads. When the dial pad is pressed, it produces a combination of two separate sine waves which is a unique frequency signal that can be decoded and produced as a binary output. MT8870 Decoder is integrated with an operational amplifier with user-adjustable Guard time. The embedded band-split filter uses switch capacitor techniques to distinguish and split low and high frequencies from the received signal.

MT8870D Key Features
- Complete DTMF (Dual Tone Multi-Frequency) Receiver
- Low power consumption
- Internal gain setting amplifier
- Adjustable guard time
- Central office quality
- Power-down mode
- Inhibit mode
- Backward compatible with MT8870C/MT8870C-1
- On-board voice input interface
- On-board LED it is very convenient to check the output state.
MT8870D Pinout

Pin Name | Pin Function | Description |
---|---|---|
Q1 | Binary Bit 1 | Binary Output Pin 1 |
Q2 | Binary Bit 2 | Binary Output Pin 2 |
Q3 | Binary Bit 3 | Binary Output Pin 3 |
Q4 | Binary Bit 4 | Binary Output Pin 4 |
StQ | Delayed String Output | Represents Binary Bit 0 |
StQ | Power Down Input | Triggers Power down sequence |
IN | Inhibit Input | Logic high inhibits the detection of tones representing characters A, B, C, and D |
VCC | DC Supply Input | 4.5V – 5.5V (5.0V Nominal) |
GND | Ground | Ground Pin of the Module |
MT8870D Specifications
- On-board MT8870 frequency decoder chip
- On-board audio input interface
- On-board LED lights for output state indication
- PCB Size: 26.5 x 24.5 mm
- Operating Voltage: 4.75 – 5.25 Volts
- Operating Temperature: -400C – 850C
- Oscillator Frequency: 3.579545 MHz
- Source/Sink Current: 10 mA
- Power Dissipation: 500 Watts
- Minimum Op-Amp Gain: 0.30 MHz
Applications MT8870D
- Receiver system for British Telecom (BT) or CEPT Spec (MT8870D-1)
- Paging systems
- Repeater systems/mobile radio
- Credit card systems
- Remote control
- Personal computers
- Telephone answering machine
Datasheet MT8870D
You can download the datasheet for the MT8870D Integrated ISO2-CMOS DTMF Receiver by clicking the link given below:
See Also: CD4059 Program Divide-by-N Counter | 74LS156 Dual 2 To 4 Line Demultiplexer (Open Collector) | HC12 SI4463 433Mhz Wireless RF Serial Port Module