This tutorial introduces you to DTMF technology and the DTMF decoder IC MT It also helps you to understand how to interface the IC to based micro . This board decodes DTMF signal either from an audio source or phone line to 4 bit binary TTL(5V) level output. It also indicates outputs with LED. Can use. Introduction. DTMF (Dual Tone Multi-Frequency) signaling is used for telecommunication signaling over telephone line in the voice frequency band between.

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DTMF Decoder Using MT

Tuesday, January 1, One can also test the IC on a simple breadboard. For now we do the hardware way.

Billy Robot Overlord Posts: It uses electronics and computer to assist in the phone line connection. To do that, install a 50K – K resistor between the tip and ring lines. We haven’t failed, we have succeeded in finding out what the problem isn’t! I can now confirm that the decofer is not the problem. As it stands, the circuit will work for a few seconds, and then lock up.

It does take a certain amount of time for the chip to identify the tone; no less than milliseconds, I think. A resource for professional design engineers. 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.


Yes, the cellphone is connected to the circuit by the audio jack.

Aug 23, 6. I will try using a potentiometer to see what is the highest resistance that will still let the chip recognize vtmf signal and see if that stops it from locking up.

This still did nothing. Try using a K resistor and see if that clears it up. I will try plugging in my computer instead and see if that changes anything, but the sound card on the computer might do the same thing as the phone and stop putting out signal. I would get a audio amp kit from Velleman or sparkfunto deal with the audio.

DTMF Receiver IC MT Tester | Electronics For You

Here is a link to the datasheet for the MT http: May 02, July 25, Please enter your name here. Power Bank for Smartphones. It is a common standard build into the decoder chip. Therefore, by adding an extra resistor and steering diode the tone duration can be set to different values. Headphone amplifier is small enough to fit in Altoids tin box, and thanks to low power consumption may be supplied from a single 9V battery.

DTMF Decoder – MT8870

When you are not pressing buttons, the output will be DC and the capacitor will look like an open circuit, the phone will think there are no ear phones connected, so it is shutting off the output a few seconds after you stop pushing buttons.


Whenever you press any key on your local telephone keypad, the delayed steering Std output of the IC goes high on receiving the tone-pair, causing LED5 connected to pin 15 of IC via resistor R15 to glow. Internship — Image Processing Engineer 27 December When a proper output is dceoder obtained in projects using this IC, engineers or 88700 need to test this IC separately. I am attempting to make a circuit with the MT chip. First I set up the circuit on a breadboard in its normal fashion, as can be seen in this diagram: In the early days, our phone system used to be operated by human operator in a telephone exchange room.

My next test will be to put a potentiometer in place of the resistor between tip and pin 2 so I can see if 88770 the resistance close to the “cutoff point” where the circuit reads the signal helps anything. The DTMF frequencies are from to Hz, so you should not have any frequency roll off decover the audio amp.