DTMF dead?

I have an upcoming project in which I might want to use dtmf transceiver chips as a simple means of communication. However, it seems that dtmf transceiver chips are quite hard to get these days. Even Digikey stocks none. Anyone knows a source that keeps making dtmf transceivers for the years to come?

--
Reply to nico@nctdevpuntnl (punt=.)
Bedrijven en winkels vindt U op www.adresboekje.nl
Reply to
Nico Coesel
Loading thread data ...

The DTMF chips were commercially viable for a few years a few decades ago. They lived on in some hobbyist projects much much longer and I'd expect the hobbyist surplus houses (BG Micro, Jameco, etc.) to still have some lying about in the bins. BG Micro seems to have the SSI-204 and 8870 decoders and the 5089 generator.

Most recent phone accessories that do DTMF decoding use custom ASIC's and aren't easily isolated to just find the DTMF parts (usually a single chip does not just the decoding but everything else too).

A DSP weenie would certainly tell you to do any DTMF decoding with a cheap DSP. 565's etc. still are around that's for sure!

Almost all recent radio-control stuff uses OOK with repeating pulse trains and seem to work pretty well. This is something easily done by tiny microcontrollers.

Tim.

Reply to
Tim Shoppa

On a sunny day (Sat, 07 Jul 2007 10:02:17 GMT) it happened snipped-for-privacy@puntnl.niks (Nico Coesel) wrote in :

There is some simple PIC code that generates DTMF tones on the Microchip site. I tried it. I am not sure if there is a decoder example too, worth having a look. I dunno if DTMF is dead, I know Ethernet and TCP/IP is alive.

Reply to
Jan Panteltje

It is possible to encode and decode the DTMF with pretty much any microcontroller. For example, you can do this:

formatting link

However, if the goal is the communication, I would rather implement a PSK or FSK modem using a microcontroller. It would be much better and even simpler then the DTMF.

Vladimir Vassilevsky

DSP and Mixed Signal Design Consultant

formatting link

Reply to
Vladimir Vassilevsky

I was hoping to use the analog front-end which is usually quite good (reception downto at least -30dB). Its hard to beat that with a microcontroller implementation (been there done that).

PSK / FSK is also an option. I just need something cheap and reliable that will communicate over a 2 wire system carrying both communication and power.

--
Reply to nico@nctdevpuntnl (punt=.)
Bedrijven en winkels vindt U op www.adresboekje.nl
Reply to
Nico Coesel

It depends mainly on the incoming SNR, not the absolute signal level. It is quite possible to over perform the standard 8870 decoder if the micro does have the internal ADC.

Been there, done that :) Perhaps, the most straightforward solution is running the UART over the power. There could be several possible ways to do that, depending on your system.

Vladimir Vassilevsky

DSP and Mixed Signal Design Consultant

formatting link

Reply to
Vladimir Vassilevsky

Tim's response is not making me happy :-(. I have to talk to a couple of hundred units connected with as little wiring as possible. In the end the communication gets concentrated into a unit which puts the messages on ethernet. However, an ethernet stack is just to big to put into a small device. Price is a big issue as is time. I hope I can use existing -proven- technology to cut development time and eliminate risks.

--
Reply to nico@nctdevpuntnl (punt=.)
Bedrijven en winkels vindt U op www.adresboekje.nl
Reply to
Nico Coesel

On a sunny day (Sat, 07 Jul 2007 21:24:53 GMT) it happened snipped-for-privacy@puntnl.niks (Nico Coesel) wrote in :

The old 8051 has a 9 bits UART, if bit 9 was set it was an address. I do not remember the name of the protocol, but you could address up to 256 units using a 2 or 3 wire system? These things were on the market long time ago.

Reply to
Jan Panteltje

If you have a DC return path beside the two wires I'd recommend using phantom power and going high speed RS-485.

You apply the DC (or AC) to the center tap and hte telemenry to the secondary. ON the two wires the power is on the common mode and the telemetry is on the differental mode.

On the other end just pick off the signals in the same order. (power on the center tap and telemetry on the secondary).

Reply to
Mook Johnson

The sort of wiring hasn't been nailed down yet, but at this moment I would prefer a system with 2 wires which carry both power and communication. RS485 is also in the picture, but we need to have up to several hundred devices on a short bus (say 20 meters / 60 feet). I think this would be stretching RS485 too much to its limits even at low baud rates. Also, the communication comes from a UART. Using a transformer on DC biased signals is not a good idea.

It also seems an NXP LPC2101 ARM micro is even cheaper ($1.65) than a NXp LPC935 8051 based micro ($1.82) so I think software FSK -which I've build before- is not out of the question. DTMF is a whole lot more complex to decode than FSK.

--
Reply to nico@nctdevpuntnl (punt=.)
Bedrijven en winkels vindt U op www.adresboekje.nl
Reply to
Nico Coesel

Is it a two way or one way communication? If it has to work in one way, the simplest way to transmit is by inversion of the polarity of the power.

It is not a problem to make a UART signal to be DC-balanced. You just have to encode the data to equalize the number of zeroes and ones.

Indeed PSK is even simple then FSK. Any microcontroller would do.

Vladimir Vassilevsky

DSP and Mixed Signal Design Consultant

formatting link

Reply to
Vladimir Vassilevsky

I think the cost of components to apply a modulation to power lines (presumably with several hundred regulators hung across them and a hefty power supply at one end) and demodulating the same is going to be a lot more than 1 or 2 extra pins on a plug and socket and an extra bit of cable. Because you were considering DTMF it sounds like you can afford to be dog slow (10 baud?). I think I would be looking at a single data line with 24v (or more) logic levels, pulled up at the master with open collector/drain drives. The receiver could probably be as crude as a high impedance voltage divider tapping down to processor logic levels. One extra connector pin, one LL MOSFET and 2 resistors - sounds cheap to me.

Reply to
nospam

Huh?

It is called power over ethernet, or poe for short.

Why reinvent the wheel when everybody else is betting on the obvious?

--
Many thanks,

Don Lancaster                          voice phone: (928)428-4073
 Click to see the full signature
Reply to
Don Lancaster

With that many devices on such a short wire, the limiting number you're seeing might just be leakage current in the drivers and it's not really being fair to take them all worst-case unless the tempurature is really 150C...

Again, don't ignore the least-common denominator of OOK. I'm not sure why you're all that worried about receiver dynamic range and the advantages of DTMF there. If you're really that price sensitive and can put enough overhead bits in to overcome noise and collisions, OOK really does work in bazillions of real world super-cheapo applications. DTMF made perfect sense for a while in the 60's when the limitations of no sequential digital logic met the bandwidth of a POTS circuit met the long-lines of a transcontinental haul. But although you haven't told us what you're doing or the full details of the environmnet, with a run of just 20M you're not in the same ballpark transmission-wise, and you are a half-century ahead in terms of microcontroller availability and ease. Use those advantages!

Tim.

Reply to
Tim Shoppa

Nico -

If your heart is set on DTMF, take a look at CML Micro.

formatting link

Click "DTMF" under the Telephony heading. Parts listed at left. Good luck. -mpm

Reply to
mpm

That is a very valid argument. But there many reasons (wiring, connectors, transformers, code size, etc ) why ethernet doesn't fit in this application.

--
Reply to nico@nctdevpuntnl (punt=.)
Bedrijven en winkels vindt U op www.adresboekje.nl
Reply to
Nico Coesel

Then make sure your application is both 8-track and ASR-33 compatible.

--
Many thanks,

Don Lancaster                          voice phone: (928)428-4073
 Click to see the full signature
Reply to
Don Lancaster

You can still use a PoE controller IC even if you don't have "real" Ethernet anywhere... they're really just your standard switching converter ICs with a simple "protocol" thrown on top to let the controller "handshake" with the power provider system.

Reply to
Joel Kolstad

WHAT? No "Model 15"?

--
Service to my country? Been there, Done that, and I\'ve got my DD214 to
prove it.
 Click to see the full signature
Reply to
Michael A. Terrell

But that still seems like an overkill for the project at hand. There is an ethernet connected device acting as a bus master. Using internet technology also comes with security issues so SSL or a similar encrypted tunneling technique is required. A proprietary bus is not easy to hack or interface (lets say it takes more than a laptop with ethereal) and thus requires less security measures. SSL alone takes about 90kB of flash and some processing power.

--
Reply to nico@nctdevpuntnl (punt=.)
Bedrijven en winkels vindt U op www.adresboekje.nl
Reply to
Nico Coesel

ElectronDepot website is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.