Author |
Message |
Christoffer
Joined: May 16, 2015 Posts: 16 Location: Denmark
|
Posted: Mon Sep 11, 2017 3:10 pm Post subject:
touch tone /dtmf rythm synth |
|
|
Hi! I'm currently in possession of fairly few synth voices, and am looking for cheap, interesting ways to create some more.
That got me looking at DTMF encoders - 12/16 buttons matrix'd in, two-tone sound out. adding some signal processing from the synth world,
VCA/VCF, and then a transistor instead of each switch in the matrix as gate input for the different sounds.
I think having a phone sound sequencer running low passed in the background as rythm could be worth exploring.
Has anybody else done similar? Google sais no.
Any ideas as to what could be added? Any reason why this is a crap idea? _________________ **************
--Christoffer |
|
Back to top
|
|
|
Grumble
Joined: Nov 23, 2015 Posts: 1294 Location: Netherlands
Audio files: 30
|
|
Back to top
|
|
|
PHOBoS
Joined: Jan 14, 2010 Posts: 5591 Location: Moon Base
Audio files: 705
|
|
Back to top
|
|
|
Christoffer
Joined: May 16, 2015 Posts: 16 Location: Denmark
|
Posted: Tue Sep 12, 2017 1:21 pm Post subject:
|
|
|
well, in reality, any landline phone has the beeps. One could just use the existing phone, enclosure and all, and break out the handset speaker to a jack and solder some transistors across the buttons. I'm sure there'd be space for some perfboard in there.
It'd be nice to make a cool eurorack module of it, though.
Maybe keeping the original button input, so you'd have a panel-mount 0..9#* keypad on there too. _________________ **************
--Christoffer |
|
Back to top
|
|
|
PHOBoS
Joined: Jan 14, 2010 Posts: 5591 Location: Moon Base
Audio files: 705
|
Posted: Tue Sep 12, 2017 3:04 pm Post subject:
|
|
|
I guess that's true at least as long as it isn't an old model with a dial. I do recall earlier phones with a key matrix
having a a switch for pulse or tone. What I am mostly wondering about is how to power it, I guess google can help
me there. If I remember correctly it is a fairly high voltage though which is higher when the phone rings. I once
got zapped installing a wall socket and somebody called at the very same moment. However, if there is a chip inside
the voltage for it is probably lower and maybe I can find a datasheet. (I haven't checked the links grumble posted,
maybe there is some info in those) _________________ "My perf, it's full of holes!"
http://phobos.000space.com/
SoundCloud BandCamp MixCloud Stickney Synthyards Captain Collider Twitch YouTube |
|
Back to top
|
|
|
Grumble
Joined: Nov 23, 2015 Posts: 1294 Location: Netherlands
Audio files: 30
|
Posted: Wed Sep 13, 2017 3:11 am Post subject:
|
|
|
At Aliexpress search for DTMF and the treasure box opens up _________________ my synth Last edited by Grumble on Wed Sep 13, 2017 4:19 am; edited 1 time in total |
|
Back to top
|
|
|
Grumble
Joined: Nov 23, 2015 Posts: 1294 Location: Netherlands
Audio files: 30
|
Posted: Wed Sep 13, 2017 4:14 am Post subject:
|
|
|
Datasheet MT8870D << CLiCK (is the receiver)
HT9200 << Datasheet of the transmitter _________________ my synth |
|
Back to top
|
|
|
PHOBoS
Joined: Jan 14, 2010 Posts: 5591 Location: Moon Base
Audio files: 705
|
|
Back to top
|
|
|
PHOBoS
Joined: Jan 14, 2010 Posts: 5591 Location: Moon Base
Audio files: 705
|
Posted: Thu Sep 14, 2017 7:54 am Post subject:
|
|
|
PHOBoS wrote: | It was a bit harder to find the datasheet for it but I found one
for a EM91401CP which looks like it's the same chip but a different brand. |
Apparently it isn't the same chip. I thought it might be as it has the same number, are both DTMF encoders, have the same amount of pins
(at least the CP version) and the Xtal is connected to the same pins. So I connected it and all I got was a bit of hum. Luckely no smoke
and the chip didn get warm either. So I retraced the connection on the PCB, which was a bit tricky as it has >50 SMD components on the
backside, to figure out how to connect it. By looking at how it connected to the other chip I did manage to find what would most likely be
the power pins, the DTMF output pin and of course the key matrix. Tried it again and this time I did get sound out of it
Apparently DTMF signals are designed to be used with a 4x4 keypad but often the last column is omitted. This telephone however has a
3x5 keypad, the bottom row doesn't produce any sounds though but it is connected to the DTMF chip so I wonder what the functions of the
buttons are. The telephone also has a switch to select tone or pulse which is also connected to the chip but I haven found the pulse output
pin yet. I think I might need to add a pullup resistor to one of the undefined pins to get that working.
So it produces sounds and they are actually quite nice. It's been a while since I used a telephone connected to a land line and I thought all
the buttons produced a distinct tone (I remember playing simple melodies on it) but that's not the case. They actually produce a combination
of 2 sinewaves.
here are the frequencies for future reference:
Code: | 1209 Hz 1336 Hz 1477 Hz 1633 Hz
697 Hz 1 2 3 A
770 Hz 4 5 6 B
852 Hz 7 8 9 C
941 Hz * 0 # D |
I was wondering why those frequencies where chosen as I didn't really see any connection between them and I found an answer here:
Quote: | The frequencies were chosen to avoid harmonics : no frequency is a multiple of another, the difference between any two frequencies does not equal any of the frequencies, and the sum of any two frequencies does not equal any of the frequencies. Although DTMF works in normal human voice range, the combination of inharmonic frequencies makes it hard for the human voice to impersonate |
I'll try to figure out what the pulse output is and I think there should be a redial function too. For that you probably have to disconnect so I also
have to figure out how that switch is connected. I do have at least 2 more telephones which I could look into and I also have a couple of toys with
telephone sounds which I've been planning ot put together in a box, so this might be a nice addition. _________________ "My perf, it's full of holes!"
http://phobos.000space.com/
SoundCloud BandCamp MixCloud Stickney Synthyards Captain Collider Twitch YouTube |
|
Back to top
|
|
|
Christoffer
Joined: May 16, 2015 Posts: 16 Location: Denmark
|
Posted: Thu Sep 14, 2017 4:15 pm Post subject:
|
|
|
Wow! nice going! I haven't even found a suitable phone yet!
Looking forward to seeing what you come up with! _________________ **************
--Christoffer |
|
Back to top
|
|
|
PHOBoS
Joined: Jan 14, 2010 Posts: 5591 Location: Moon Base
Audio files: 705
|
Posted: Sat Sep 16, 2017 6:40 am Post subject:
|
|
|
I tested a chip from another telephone, the UM91610A. This time I was able to find some scans of a datasheet and
an example circuit. I connected it, powered it up but it didn't seem to do anything at least I didn't get anything from
the tone output. This output isn't used in the example circuit I found, as a matter of fact it is attached to GND which
I found rather odd. It also has a pulse output so I tried that and I do get pulses from it so the chip does work. I
noticed in the datasheet that the tone output can be used to drive a piezo directly. It could be that this piezo has to
be connected between that pin and Vdd which means it only pulls it to GND. So I added a pullup resistor and this time
I did get a tone out but it just gives a (squarewave) beep with the same frequency whenever you press a key. This is
actually what it says in the datsheet and as a it turns out the UM91610A isn't a DTMF chip
I could still use it for the pulse outputs but there is a delay between pressing a key and getting the pulses out. It does
have a redial function though which could come in handy. Also the oscillator it uses is created with two resistors and a
capacitor which makes me think it just has two built in inverters similar to the CD4060. This means I can easily adjust
the frequency and as a result the timing of the pulses and the frequency of the tone output. It might even be possible
to connect an external oscillator to it but I did notice the oscillator only starts running whenever you press a key and it
stops a couple seconds after you release it. I'm not sure what to use it for yet, I could use the pulse output to turn the
tone output on/off but you could do something similar and probably more useful with a quad NAND chip. Hmm, maybe
I could use the pulse output to 'fill' a shifregister which in turn is used to 'press the keys' and maybe change the
frequency as well. _________________ "My perf, it's full of holes!"
http://phobos.000space.com/
SoundCloud BandCamp MixCloud Stickney Synthyards Captain Collider Twitch YouTube |
|
Back to top
|
|
|
|