Arduino library for MT8870 DTMF decoder (breakout).
This library reads the signals of the MT8870 chip. If data is available one can read it raw or as text.
DTMF = Dual Tones Multiple Frequency. These are the tones you hear when you press buttons on your phone.
DTMF tones, uses one frequency from A..D and one frequency from E..H.
| Name | Frequency |
|---|---|
| A | 697 Hz |
| B | 770 Hz |
| C | 852 Hz |
| D | 941 Hz |
| E | 1209 Hz |
| F | 1336 Hz |
| G | 1477 Hz |
| H | 1633 Hz |
| char | low freq | high freq |
|---|---|---|
| 1 | 697 Hz | 1209 Hz |
| 2 | 697 Hz | 1336 Hz |
| 3 | 697 Hz | 1477 Hz |
| A | 697 Hz | 1633 Hz |
| 4 | 770 Hz | 1209 Hz |
| 5 | 770 Hz | 1336 Hz |
| 6 | 770 Hz | 1477 Hz |
| B | 770 Hz | 1633 Hz |
| 7 | 852 Hz | 1209 Hz |
| 8 | 852 Hz | 1336 Hz |
| 9 | 852 Hz | 1477 Hz |
| C | 852 Hz | 1633 Hz |
| * | 941 Hz | 1209 Hz |
| 0 | 941 Hz | 1336 Hz |
| # | 941 Hz | 1477 Hz |
| D | 941 Hz | 1633 Hz |
Feedback as always is welcome.
#include "MT8870.h"- MT8870() constructor
- void begin(uint8_t STQ, uint8_t Q1, uint8_t Q2, uint8_t Q3, uint8_t Q4)
defines which pins to use.
Technically it is possible to have readout multiple decoders
with one MT8870 object by calling begin() with other pins.
- STQ = data available signal
- Q1..Q4 = data pins.
- Calling begin resets the lastRead char
- bool available() returns true if there is a DMTF signal
- char read() reads the character available. Returns MT8870_NOKEY == 255 if no signal available.
- uint8_t readRaw() returns 0 .. 15 or MT8870_NOKEY == 255 if no signal is available.
- uint8_t lastRaw() returns the last code read 0 .. 15 or MT8870_NOKEY == 255 if no signal available. Note this is a cached value from a readRaw / read call.
- uint32_t lastTimeRead() returns the timestamp of last read() or readRaw().
- improve documentation
- keypad matrix, which key generates which tones.
- test setup
- add examples
- DMTF with a PCF8574
- DMTF as secret key
- DMTF with less keys (less pins)
- DMTF over interrupt triggered by STQ line
- buffer like Serial? (how to fill? interrupt? example sketch?)
- read part of stream interface?
- DMTF tone generation?
- MCP_DAC
- PWM + HW?
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Thank you,
