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DTMF 8870 decoder from NOKIA 3310

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aljamri

Member
I am trying to get a 4-bit data sent by mobile (Nokia 3310), using DTMF decoder MT8870 through the headset.
That is in short my project. I am in the stage of components collection. Is it possible to get this project work or not? Please all your advice is appreciated, and any small tips may make difference.
salam
 
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mramos1

Active Member
I worked for Mitel (MT) for 15 years. You lost me on the "through the headset".

Can you give more details?
 

aljamri

Member
Sorry, this shows how much I don't know about the subject. I'm trying to connect the mobile earphone wire into the decoder input terminals, and I'll put my mobile on auto answering mode ( after 3 rings) then I'll press the numbers of my mobile to give beeps, is that signal clear and strong enough to be decoded or not? Thanks for trying to help me.

salam
 
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akg

New Member
aljamri said:
Sorry, this shows how much I don't know about the subject. I'm trying to connect the mobile earphone wire into the decoder input terminals, and I'll put my mobile on auto answering mode ( after 3 rings) then I'll press the numbers of my mobile to give beeps, is that signal clear and strong enough to be decoded or not? Thanks for trying to help me.

salam
Yes tha would work, provided you have a good mobile signal strength
 

aljamri

Member
mramos1 said:
There are many DTMF decoders. Ramsey has a kit based on another chip.
.
Thanks mramos for your interest to answer, but two things I've not put clear, those places are remote and no land line is provided

mramos1 said:
What is the range you are tring to control things from? A 2 mile walkie-talkie would save on the monthly phone bill. Make a DTMF generator and receiver.
In my country we have prepaid service (SIM) that will last for one year for less than $60 credit. and by the end of the year you can transfer your credit into another SIM account ( the balance ), with no any other bills.

Regardless all of these things, building a project and seeing it functioning is a great childish pleasure I'm ready to lose money for.

Thanks a lot
 

mramos1

Active Member
Should be a challenge. I assume the phone is in a good environment, your auto-answer will get amplified to a DTMF decoder. Then a PIC of something will process the digits and do something?

Did you see the PIC only DTMF page I put up?
 

aljamri

Member
I'm KG1 in PIC

mramos1 said:
Did you see the PIC only DTMF page I put up?
Thanks again mramos1, I'm in my 6th grade in electronics, but in microcontroller, I'm just KG1 (ask my dear teacher Mr. Nigel Goodwin ). So that I am quite sure that using PIC will make it much pro, that is in my mind and I'll include it in my next version of this project. At this stage, what I need is to get 4-bit output (16 options). Then I'll connect some relays and that will do my project.

mramos1 for sure I'll need your suggestions during my progress in PIC study and many of my doubt will need your valuable answers

thanks again and again
 
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mramos1

Active Member
Even with the 4 bits from the DTMF decoder, you will need to read them and have a processor deal with them, if you are doing real control apps.
Also have an interface to the decoder chip.

Is this is a school project? Maybe just light up 4 LEDs.

So you are in the 6th grade? Wish my kids here in the US were doing electronics in the 6th grade. I have scopes, just sold my 8051 emulator.
PICs and Atmel chips and programmers all over..

They like sports and video games. I will fix the video game part soon though.. Too many hours wasted.
 

aljamri

Member
akg said:
Yes tha would work, provided you have a good mobile signal strength
Thanks akg for your answer. Today I've measured the output of the mobile earphone while I'm pressing numbers on the telephone I used to call and found it nearly 300mV. Is that strong enough?

I tried to measure the frequency for different digits using my FLUKE 79 with Hz meter but they seem not stable and nearly the same, that's may be because its composed of two frequencies. Any Idea.... Any body...?

thanks for all
 

Nigel Goodwin

Super Moderator
Most Helpful Member
aljamri said:
Thanks akg for your answer. Today I've measured the output of the mobile earphone while I'm pressing numbers on the telephone I used to call and found it nearly 300mV. Is that strong enough?
If not it's simple to amplify it - but how did you measure it?, a multimeter may not measure it very well.

I tried to measure the frequency for different digits using my FLUKE 79 with Hz meter but they seem not stable and nearly the same, that's may be because its composed of two frequencies. Any Idea.... Any body...?
As you say, it's two frequencies, so you can't measure it with a frequency meter.
 

akg

New Member
aljamri said:
Thanks akg for your answer. Today I've measured the output of the mobile earphone while I'm pressing numbers on the telephone I used to call and found it nearly 300mV. Is that strong enough?

I tried to measure the frequency for different digits using my FLUKE 79 with Hz meter but they seem not stable and nearly the same, that's may be because its composed of two frequencies. Any Idea.... Any body...?

thanks for all
i would suggest you to construct the decoder and work with it , rather than fiddling with the o/p signal strength too much..after all , as suggested above , if reqd we can very well amplify that. well my concern is ,if you send a sequence of tone to the mobile and there is signal fading , then the decoder will miss some tones , that can cause unintentional working of your device.
 

aljamri

Member
We are both in the same thought !

mramos1 said:
Even with the 4 bits from the DTMF decoder, you will need to read them and have a processor deal with them, if you are doing real control apps.
Also have an interface to the decoder chip.
Yes that is correct all that in my mind. In later stages, all these issues will be discussed thoroughly.

mramos1 said:
Is this is a school project? Maybe just light up 4 LEDs..
No it will be put in actual process control of remote pumping stations.

mramos1 said:
So you are in the 6th grade?
Nooooooooooo .... That's a joke. I spent almost 4 decades enjoying this life, started knowing about electronics (series and parallel resistors) since 1984, but not in depth.

mramos1 said:
I have scopes, just sold my 8051 emulator.
PICs and Atmel chips and programmers all over..
As you see, while you are thronging your emulator, I've just started learning what is the emulator, that's what I call KG1

thanks a lot..
 

aljamri

Member
:confused:
Nigel Goodwin said:
a multimeter may not measure it very well.
As you say, it's two frequencies, so you can't measure it with a frequency meter.
Thanks Nigel, as I said I connected my multimeter in parallel with my earphone wires. The reading was so stable after sending digits from sending telephone on almost 300 mV. Then I tried all the keypad of the sending telephone and got same voltage with same stability.
When I tried to measure the frequency the same way, I could not get stable readings. After many attempt I got no any two similar readings. However, it is clear that there is a range started from almost 600 Hz (Key 1) up to 1.1 kHz (key 0).
 
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aljamri

Member
Don't worry !

QUOTE=akg]i would suggest you to construct the decoder and work with it , rather than fiddling with the o/p signal strength too much. after all , as suggested above , if reqd we can very well amplify that. well my concern is ,if you send a sequence of tone to the mobile and there is signal fading , then the decoder will miss some tones , that can cause unintentional working of your device.[/QUOTE]

thanks for your series of replays that made me more excited. I like it when you used We in your replay this is one reason why I enjoyed being a member Electro Tech this what i call Team Sprit

about service shading I don't think it is big concern since I need only a press to just one key to control the process. In later stage I'll use the mobile mic ( not earphone ) to give sort of feed back. But let us keep this for later discussion.

thanks and bye for now
 

aljamri

Member
Please helpl my again

hello everybody, again im here asking for help again, i could not find the recomended crystal oscillator for this project (3.579545 MHz). is there any alternative to this ?

Thanks
 

Nigel Goodwin

Super Moderator
Most Helpful Member
aljamri said:
hello everybody, again im here asking for help again, i could not find the recomended crystal oscillator for this project (3.579545 MHz). is there any alternative to this ?
Assuming this is for the DTMF chip?, it obviously has to be exact - as everything is derived from the crystal. It should be available from sources that stock the chip, or you may need to have one made.
 

mramos1

Active Member
The 3.58Mhz xtal is old but around. It was used for color burst in TV.

Here is am 8870 schematic, the first gif.

ftp://members.aol.com/pdrunen/schematic/

EDIT: gif2 is closer to what you want. Also, that is a crystal, you called it an oscillator, that is why Nigel said you can build one.
 
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HarveyH42

Banned
Could you post a schematic when you are done? I'm sure there are a few muslims that would love this circuit... (sorry, about that :) )

Actually, I work irregular hours and it would be great to dial up the home phone and turn on/off stuff. Mostly I'd like to control some of my home security functions remotely. Like arm/disarm the alarm and select which cameras are being recorded.

Sorry about the terrorism crack, but I got razzed pretty good last month for helping on a robotics project, that some people though was inappropriate. I thought it improbable that it would never be built (time, money, and practical function), so I outlined the various sub-systems that this guy would need to develop, then all hell broke loose.
 
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