Dual Tone Multi Frequency (DTMF) is also known as touch tone. The DTMF system uses a set of eight audio frequencies transmitted in pairs to represent 16 signals, with numbers 0 through 9, the letters A to D, and the symbols # and *. See chart below. The signals may be generated on your ham radio by pressing the push to talk (PTT) button and one of the keys on the key pad. The audible signals can be transmitted to another radio to control an action such as turning on a lightbulb miles away.
Decimal Binary Key 0 0000 D or Exit 1 0001 1 2 0010 2 3 0011 3 4 0100 4 5 0101 5 6 0110 6 7 0111 7 8 1000 8 9 1001 9 10 1010 0 11 1011 * 12 1100 # 13 1101 A or UP 14 1110 B or DOWN 15 1111 C or MENU
I used a Baofeng radio with a male 2.5 mm tip, ring, sleeve (TRS) stereo audio plug connected from the radio speaker jack to the input of the MT8870 DTMF Voice Decoder Module. (Click here for a pinout diagram of the Baofeng plug.) The Q1 output pin from the DTMF decoder is connected to the input pin of the Relay Module. The common (COM) and the normally open (NO) connections on the Relay Module are connected to the severed "hot" smooth wire of the AC extension cord.
The DTMF Decoder Module and the Relay Module requires a 5 Volt Direct Current (VDC) source. I supplied the 5 VDC with a 9 volt battery and a Step Down Buck Converter to reduce 9 VDC to 5 VDC. You can also use any USB connector for the 5 volt supply.
When you press the PTT button and the number "1" key on the local or remote radio, the relay will be energized, turning on what ever is plugged into the electrical cord, like a 120 VAC light bulb. Pressing the "Exit" key will turn it off.
Parts List at Amazon.com (you only need one of each) MT8870 DTMF Voice Decoder Decoding Module $ 7 for 2 5V One Channel Relay Module Relay Switch $ 6 for 2 MP1584EN DC-DC Buck Converter $11 for 6 TRS Male Plug 3 Pole Stereo 2.5mm Connector $ 7 for 4
This project uses a Baofeng radio, a DTMF decoder, and an Arduino to control 4 relays and transmit a voice confirmation message.
The dual tone is transmitted from a distant radio to the local radio via the PTT button and the key pad. The tone is decoded by the MT8870 DTMF module and translated to 4 digits, displayed by 4 light emitting diodes (LEDs). The output from the DTMF module is fed into the Arduino where it determines which relays to turn on. The Arduino sends a voice message through the local radio to the distant radio informing the user which relays were turned on.
A male 2.5 mm TRS stereo audio plug is used to connect the output from the radio speaker to the input of the DTMF decoder. A male 3.5 mm TRS stereo audio plug is used to connect the radio's PTT button and microphone to the Arduino.
A PC817 optocoupler, and a 200 ohm resister, are used as an electronic switch for the radio's PTT button. A 1 uF capacitor is used to connect the voice output from the Arduino to the microphone input of the radio via the 3.5 mm plug.
The voice comes from the Talkie Library at https://github.com/going-digital/Talkie. The website explains how to download the code and include it into your Arduino libraries folder.
Click here for the Voice Library.
Click here for the Arduino code.
Click here for the Schematic.
For more information, please email me at: WO4ROB@gmail.com
Check out the video at the following YouTube website to see a demonstration on how it works: https://youtu.be/b9nXncWf5vg
Parts List at Amazon.com (you only need one of each) MT8870 DTMF Voice Decoder Decoding Module $12 for 10 Arduino Nano $20 for 4 4-Channel 5v Relay Module $ 8 for 1 PC817 Optocoupler $ 5 for 10 TRS Male Plug 3 Pole Stereo 2.5mm Connector $ 7 for 4 TRS Male Plug 3 Pole Stereo 3.5mm Connector $ 9 for 10 200 ohm resister $ 5 for 25 1uF capacitor $ 4 for 50 9v battery $11 for 8
