Sound or Tone input to a Pi

[spmathis]

Not sure if the beginner forum is the right place to post this but I'm a beginner with the Pi so I hope the is the right place.

I'm finding a lot of information about sound on the PI, specifically about sound generation but I haven't been able to find anything on reading sound, specifically any abilities to read tones and recognize their frequencies. I'm working on having the ability to read touch tone off of the standard phone system and was wondering if anyone has worked with or knows about any hardware that can translate (or read) tones, either from a mic or directly off of a phone receiver.

Would appreciate any help in this area.

Thanx!

[DougieLawson]

There's no sound input device on a RPi. So you're either going to need a sound card that connects on the GPIO pins or you'll need a USB sound card.

[spmathis]

There's no sound input device on a RPi. So you're either going to need a sound card that connects on the GPIO pins or you'll need a USB sound card.

Thanx Doug - I'll have to look for a USB sound card (though I don't think I've ever seen or heard of one...

[Douglas6]

I'll have to look for a USB sound card (though I don't think I've ever seen or heard of one...

There are a ton out there, I have a couple based on the CM108 chipset that are good and cost around $5. But I would research tone detection chips first. 35 years ago Radio Shack had one for DTMF. Coding tone detection software is not trivial; do some research on the Raspberry Pi and FFT. You might also look at the 'Aubio' Python library.

[SiriusHardware]

If your interest is purely in decoding DTMF tones like those used by touch tone telephones then it would be much, much easier to use a dedicated DTMF decoder chip to handle the tone side of the tone input.

For example, there's the MT8870, which has a 4-bit parallel data interface (+ strobe) or the MT3370 which has a simple 'serial' data output format.

Typically, ICs like this use just a few components and a commonly available 3.57Mhz crystal. All of them output digital-level signals which represent the tones being received, although you might want to look for a chip which is specifically 3-volt friendly, otherwise you will have to use level converters or dividers between the chip and the Pi.

[ame]

I'll have to look for a USB sound card (though I don't think I've ever seen or heard of one...

There are a ton out there, I have a couple based on the CM108 chipset that are good and cost around $5. But I would research tone detection chips first. 35 years ago Radio Shack had one for DTMF. Coding tone detection software is not trivial; do some research on the Raspberry Pi and FFT. You might also look at the 'Aubio' Python library.

DTMF decoding is trivial using the multimon program. The DTMF decoding chips are hard to get these days and quite obsolete.

As for USB sound cards:
http://www.dx.com/s/usb%2bsound?PriceSort=up

Starting at about $2.

[Douglas6]

Yikes, I seem to be targeted. But there you go, try multimon.

[ame]

Yikes, I seem to be targeted. But there you go, try multimon.

No. I could easily have replied to SiriusHardware.

[SiriusHardware]

Yikes, I seem to be targeted. But there you go, try multimon.

No. I could easily have replied to SiriusHardware.

Indeed, but we use several different DTMF decoder ICs in quite a lot of the products we make where I work - I haven't noticed that we are suffering from any shortage of them and we make tens of thousands of such products every year.

The manufacturers spent a lot of time over the years honing these things to reject false signals, cope with a wide range of input signal amplitudes, etc - that's a lot of useful work which your software then doesn't have to care about.

Any and all working solutions are valid but for a from-scratch effort, a hardware decoder IC combined with relatively simple reader code is always going to be easier than trying to write your own two-tone decoder software from scratch.

If there are prebuilt software modules or solutions etc already out there, then that's great.

[Navyscourge]

There is this blog: http://asliceofraspberrypi.blogspot.co. ... evice.html

I have this device (a pack of 3! - cheap) but have not yet tried to get it working. Maybe soon

[spmathis]

Thanx everyone the has responded to this post. a lot of things for me to look into but that's what I'm here for.

Thanx again. I'll post back with what I find.

[jwl]

Decoding DTMF in software is not difficult and does not require a lot of processing power.
Here is an example which generates and decodes the tones.

https://github.com/wb2osz/direwolf/blob/master/dtmf.c