A versatile DTMF Decoder unit with on board relay

Interrogateable opto coupled input. 

Selectable 4 digit security code to prevent unauthorised  operation

Optional Morse transpond gives feedback that relay has switched or on the condition of the input



Out of stock

Our DTMF Opto kit is a very versatile DTMF Decoder.

There is one relay output offering clean contacts, and one Opto coupled input offering complete isolation from the circuit being monitored.

You can switch the output on/off remotely with or without a 4 digit security code. The decoder also has a TX keying output to key a transmitter for transponding a Morse confirmation. There is also an audio output for the Morse audio tones.

The PCB has been designed to allow 3 input configurations – unbalanced audio, an Electret microphone or balance audio to be connected. The built version has the unbalanced input configuration.

The Opto input can be interrogated and a Morse confirmation received confirming the current state (on or off).

It’s easy to turn the output on/off. Just send the decoder its ID followed by 0 and * for ON or # for OFF e.g. 12340* turns the output on and 12340# turns the output off.

And if you want to toggle the output, just send for example 12340A and the state of the output will be changed to the opposite of its previous state. The Morse transpond will be confirmation of the new state. If you want to pulse the output send e.g. 12340B and the output will turn on for 0.5 seconds – the Morse transpond will be 0 P.

PLUS you can now use 9 for A and 8 for B with 12 key DTMF pad.


For confirmation of the switching of the output the decoder will key a Transmitter and respond in Morse code. Turning on the output will respond as 0 ON in Morse, and turning off the output will respond as 0 OFF. There is a 2 second transpond delay followed by a 400ms link establishment delay to allow for CTCSS (if used).


You can also interrogate the current state of the Opto 1 input by sending the ID followed by 1* e.g. 12341* and the decoder will transpond in Morse 1 OFF or 1 ON depending on the input state.


It’s easy to change the 4 digit security ID. Simply fit a jumper to the middle 2 pins of CN3, powering up the decoder and sending it a new 4 digit ID with DTMF. Remove power, remove jumper, then power-up and your new ID is set. If no ID is required then simply program the ID as 0000 and on next power-up no ID will be needed and e.g. 0* will turn on the output.


You can choose to turn off the Morse transpond. When setting the 4 digit identity, just add a fifth digit as 9 and the Morse transpond will be turned off. Any other character in the fifth position turns the Morse transpond on. When supplied the identity is 1234 and the fifth digit is set as 0. You do not need to program the fifth digit if transpond is desired, the fifth digit is not used as part of the identity.

The PCB is a high quality Gold Plated double sided PTH (plated through hole) 1.6mm FR4 (Fibreglass) board 64 x 38mm in size.

CN3 can also be used for in-circuit re-programming of the PIC with your own code.


  1.  How about using the kit as a DTMF code lock; use a mobile phone’s keypad tones and use the microphone option for pick up. Or…
  2.   DTMF remote control with relay O/P over radio or mobile phone, with input interrogation or…
  3.   Repeater remote close down?



2 x 10K resistors for alternative configuration, a compact Gold Plated PCB, kit components and pre-programmed PIC. See the PDF for instruction details and component list.


pdf_symbol[1]Download DTMF Opto Kit PDF 


pdf_symbol[1] Laden Sie DTMF Opto Decoder Bausatz PDF


pdf_symbol[1]HT9170 datasheet


pdf_symbol[1]Amateur Radio TNC Connector to DTMF wiring information

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