Hi. I have this dual tone multi function encoder for over 30 years, now I need a few more. The keypad on one side, a small speaker on the other side emits the tones, works with AA cells :
12 or 16 keys. Do you know of a source ?




And looking for a DTMF decoder either with microphone or earphone level input. Turns on a relay when a certain sequence of few digits is sensed. Or, what terms to use in a search ?

 

A similar device used to be sold by RADIO SHACK, a while back. I have never seen a battery powered stand-alone receiver marketed.

 

Hello,

Here are a couple of pages with decoder circuits:
http://www.electronics-diy.com/dtmf-decoder-using-mt8870.php
https://www.instructables.com/DTMF-Touch-Tone-Decoder-Using-Microchip-PIC-Microp/

Bertus

 

I have played around with a few both Encoders and Decoders. Here is an Encoder example and here is a Decoder example. I like the linked decoder because it offers the Q1, Q2, Q3 and Q4 outputs easily read by just about any uC. Note that those modules I linked to do not require a Uc to function, they work fine stand alone.

Ron

 

Are you watching a keyboard encoder or a decoder? I wrote an encoder for my C64 back in the day.
Search “ dial tone keypad”. You will still have to make it but it gets you very close to what you're after.
Dial Tone Keypad

 

Are you watching a keyboard encoder or a decoder?

Thanks;
Solved the encoder part; now am after a non-microcontrolled DTMF decoder that will open an entry gate when the proper sequence of DTMF shows up within a time window. Like long ago, entering a key sequence to retrieve answering machine messages...
I have one for 30 years from a defunct manufacturer, unable to find the same. Uses a SSI-202 + CD4514 + LS7220. Not easy to find lately and have not found a modern 'breakout' board/module or kit.

 

Thanks;
Solved the encoder part; now am after a non-microcontrolled DTMF decoder that will open an entry gate when the proper sequence of DTMF shows up within a time window. Like long ago, entering a key sequence to retrieve answering machine messages...
I have one for 30 years from a defunct manufacturer, unable to find the same. Uses a SSI-202 + CD4514 + LS7220. Not easy to find lately and have not found a modern 'breakout' board/module or kit.

I gave you a link to a decoder which is a plain jane stand alone as in no uC is needed as I pointed out. It has a Q1, Q2, Q3 and Q4 output. You will need to make a gate array using discrete components if that is what you want. Here is an example. Since the decoder outputs a BCD format you want to get to a decimal output and any of several BCD to Decimal converter chips will work just fine. Common 5 volt logic chip like the 7442 will get you 0 through 9. Here is another example using a 7442 BCD to Decimal decoder IC.

Ron

 

I bought two of those DTMF decoders, quite cheap,on line. no hint as to the connections at all. Had to trace out to find the power connection, guessed at the signal input.

 

What is the application?
You can program any keypad to be a coded entry system. You don't need the DTMF function for this.

 

Hi. Yes, I want the DTMF to modulate RF and the receiver audio to unlock entry when the correct sequence of 4 tones matches within a time window.

Correct DTMF sequence received within time---->open lock---->start 5 minute timer---->lockup---->reset DTMF decoder

 

I saw several during my keyword search but I wasn't really sure what you were looking for at the time.

I think you missed several items in my previous post would you go back and review it one last time?

https://forum.allaboutcircuits.com/threads/looking-for-dtmf-gadgets.207766/#post-1996898

 

You can do it differently without DTMF.
Enter pass code on keypad. Send digital code to unlock.

 

I bought two of those DTMF decoders, quite cheap,on line. no hint as to the connections at all. Had to trace out to find the power connection, guessed at the signal input.

Same here. However, while inexpensive these Chinese modules aren't exactly bursting with data sheets. This is an example of what I played around with.

Fortunately the I/O pins are clearly marked up. The jack is just another signal in.

Hi. Yes, I want the DTMF to modulate RF and the receiver audio to unlock entry when the correct sequence of 4 tones matches within a time window.

Correct DTMF sequence received within time---->open lock---->start 5 minute timer---->lockup---->reset DTMF decoder

Then I suggest you Google "Cipher Locks Circuits". While I see no need for DTMF you can use it if you like.

While you oppose using a uC using a single simple uC with a module like I posted above would make this project much easier. However that is your call.

Ron

 

You can do it differently without DTMF.
Enter pass code on keypad. Send digital code to unlock.

Hi MrChips. I do not know how.
To open a bunker door at a 60Km distant hilltop housing a radio repeater for maintenance. Keying the sequence on a handy-talkie keypad transmits DTMFs to the repeater which unlocks the entrance. It is done it that way to turn on/off features at repeater sites; battery charger, solar source...

How is a "digital code" sent to a receiver ?

 

This might work for you. It says "four bits" when it means "four digits".

 

Just to give an example, I have built a light that can be turned ON and OFF remotely via bluetooth.

The control box transmits 8-bit codes, one for ON and another for OFF.
The actual codes do not matter much, except that I have chosen the codes to reduce the chances of false positives and false negatives. In other words, I don't want the light to miss valid transmissions (false negative) or to be activated on random noise (false positive).

 

Just to give an example, I have built a light that can be turned ON and OFF remotely via bluetooth.

The control box transmits 8-bit codes, one for ON and another for OFF.
The actual codes do not matter much, except that I have chosen the codes to reduce the chances of false positives and false negatives. In other words, I don't want the light is miss valid transmissions (false negative) or to be activated on random noise (false positive).

You are certainly correct that DTMF is not needed in the way it once was. But, it does have legitimate use cases and (unless I am mistaken) the TS has one of these.

The project has a constraint that would be much harder to satisfy with an arbitrary digital solution: the communications channel isn't just "wireless", it is regulated land mobile radio.

Just like the case of amateur repeater control, using audio passband signaling offers a greatly simplified, (and within the domain) universal, solution. FCC regulations limit the sort of remote control that can be used on various bands. DTMF's bandwidth requirements are very specifically the same as phone transmissions. This means there is no concern about bandwidth or radio modifications to make it work.

For many applications, digital signaling is superior. In this case, DTMF has some special strengths.

 

Keypad

 

Hi MrChips. I do not know how.
To open a bunker door at a 60Km distant hilltop housing a radio repeater for maintenance. Keying the sequence on a handy-talkie keypad transmits DTMFs to the repeater which unlocks the entrance. It is done it that way to turn on/off features at repeater sites; battery charger, solar source...

How is a "digital code" sent to a receiver ?

Years ago, during the early 80s a gent named Forrest M. Mims III published an Engineers Notebook for the old Popular Electronics magazine. The paperback book I mentioned actually shows you a simple and crude method for sending STMF tones using an old pair of Handi Talkies. The book can be found here. I suggest you look at page 108 of the linked book. You will need a simple encoder on one end and a decoder on the other end. Keep in mind this is all discrete components which is what you seem to want. The old 567 tone decoder chip is long obsolete but the concept holds true. Your 60 Km is a long way a little over 37 Miles and to cover that you will need a good Handy Talkie. They do make Handi Talkies with a DTMF keypad but they aren't cheap and operate in the business band. Then too, 37 miles (60 Kilometers) is a pretty long distance. If the receiver site has phone service using a phone may be the best way to go.

Ron

 

DTMF is handy for control schemes because it is quite resistant to false triggers from noise. Sensing four BCD/TT 4bit digits can be done with a lot of CMOS gates and FFs, or some really slick cheating. that includes a counter. That all depends on being creative, and the level of security needed.