The DTMF decoder 2 is a useful tool used for decoding DTMF (Dual Tone Multi frequency) generated by telephones. The decoded digits are viewed on a 16x2 LCD screen. The DTMF decoder can be directly connected to a Serial port to view the digits in HyperTerminal on a computer. The decoder stores the last 234 received digits in EEPROM. The contents of EEPROM can be viewed on the LCD screen via two scroll buttons. Total power consumption is 12mA. The DTMF decoder has two inputs. A RJ11 jack for connecting to the phone line and a 1/8" audio jack for connecting to a scanner, tape recorder or other audio output device.
The list includes parts for the DTMF Decoder. All part numbers are for Digikey unless their is a link to another supplier.
| Quantity | Value | Description | Digikey Part No. | Component |
| 1 | 78L05 | +5V Regulator | 296-1365-1-ND | U1 |
| 1 | MCP120 | Supply Supervisor | MCP120-450DI/TO-ND | U5 |
| 1 | AT90S2313 | Microprocessor | AT90S2313-10PI-ND | U2 |
| or | Alternative Micro | ATTINY2313-20PI-ND | U2 | |
| 1 | MT8870DE | DTMF Decoder | E-SONIC | U4 |
| 1 | 4N25 | Opto-isolator | 160-1300-5-ND | U3 |
| 1 | 10uF | Dielectric | P10316-ND | C1 |
| 4 | 4.7 uF | P1199-ND | C6,7,9,10 | |
| 3 | 0.1 uF | P4525-ND | C2,4,8 | |
| 2 | 18pF | P4840-ND | C11,C12 | |
| 1 | 4.7K | 1/4 Watt | 4.7KQBK-ND | R4 |
| 3 | 10K | 1/4 Watt | 10KQBK-ND | R1,2,6 |
| 2 | 47K | 1/4 Watt | 47KQBK-ND | R7,R8 |
| 1 | 390K | 1/4 Watt | 390KQBK-ND | R9 |
| 1 | 20K POT | Vertical POT | 36G24-ND | R5 |
| 1 | 16x2 | LCD | 73-1025-N | LCD |
| 1 | RJ 11 Jack | CCM9000-ND | Phone | |
| 1 | 1/8 Audio Jack | CP-3543N-ND | Audio | |
| 1 | 9V Connector | BS6I-HD-ND | Batt | |
| 1 | 20-pin Socket | A9420-ND | ||
| 2 | Push Buttons | P8006S-ND | S1,S2 | |
| 2 | 0.1" | 7-pin Header strip | WM4005-ND | |
| 1 | 3.579545 Mhz | 3.58 Mhz Crystal | 300-6001-ND | Y1 |
| 1 | Female | DB9 Connector | A2047-ND | DB9 |
