Introduction. DTMF (Dual Tone Multi-Frequency) signaling is used for telecommunication signaling over telephone line in the voice frequency band between. DTMF Decoder MT on | This circuit detects the dial tone ( DTMF Tone) from a telephone line and decodes the keypad. Using MT DTMF Decoder With Arduino: DTMF DECODERS Are used to detect DTMF TONES Genrated by mobile phone DTMF this project we .

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I tried unplugging the power and plugging it back in.

DTMF Decoder MT |

Deoder will try using a potentiometer to see what is the highest resistance that will still let the chip recognize the signal and see dtmt that stops it from locking up. In this article, we are use the IC MT, the main component to decode the input dial tone to 5 digital output. Possibly the capacitor between tip and the now 10k resistor? It does take a certain amount of time for the chip to identify the tone; no less than milliseconds, I think.

It’s a minor point, but the way the cap is in the circuit, it is not filtering noise, it is filtering DC signal, so if the audio from the phone has a DC offset, the DC is blocked and only the AC audio gets through. When you are not pressing buttons, the output will be DC and the capacitor will look like an open circuit, decodr phone will think there are no ear phones connected, so it is shutting off the output a few seconds after you stop pushing buttons. It uses electronics deckder computer to assist in the phone line connection.


This seemed to cause a slight “lag” in the response time, but it still locked up the same. This digital output will be read in by a computer, which will then act as a operator to connect the caller’s telephone line to the designated phone line. So I tried using less resistance between decover and pin 2. Notice that there are key tone for A B C and D. Leave a Reply Cancel reply You must be logged in to post a comment.

Problems with MT DTMF Decoder

These digital bits consists of pressed key code 4-bit and 1-bit to tell that data is available. November 18, Logic 0 ‘0’ press and hold TOE: Logged jwatte Supreme Robot Posts: As it stands, the circuit will work for a few seconds, and then lock up.

Well, it was worth a shot. This LC Meter allows to measure incredibly small inductances making it perfect tool for making all types of RF coils and inductors. You could also confuse this high side driver with a capacitor in series with the output, just as you’re doing to the phone.

Using the multimeter, all voltages and continuities on the board are appearing correct.

May 09, Schematics and BOM is provided below for your reference. May 01, Here is a link to the datasheet for the MT http: Logic 0 ‘1’ press and hold TOE: I understand that the resistors at the top left of the diagram are for controlling the op-amp, but I don’t understand exactly how they do that. After a few seconds of playing with the buttons, the whole thing suddenly stopped responding.


Decoding Stmf was originally decoded by tuned filter banks. The circuit is relatively simple and straight forward, and all components can be easily found.

MT8870 DTMF Audio Decoder Module

Its decoder uses digital counting techniques to detect and decode all 16 DTMF tone pairs into a 4- bit code. Very small, roughly about my thumb size. But, again, after a few seconds it stopped responding.

It’s not late until its two, then it’s too late. It’s small, power efficient, yet customizable through onboard 2 x 7 perfboard that can be used for connecting various sensors and connectors. The problem is something with the decoded.

After a lot of googling, an obscure forum post in an indian forum stated that the k resistor between tip and pin 2 works for old Nokias, decpder is too strong for modern phones. Try using a K resistor and see if that clears it up. VegaObscura Robot Overlord Posts: Logic 0 release from button ‘2’ TOE: Logged asif Beginner Posts: Get Your Ad Here.


I need to do this with a modern smartphone. Do you have an oscilloscope or logic analyzer that you can connect to diagnose what is going on when it’s locking up? Again because when you’re not pushing buttons it decides there are no longer ear phones connected.