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DTMF Based Robot

Son Kumar




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DTMF is the acronym for Dual tone modulation frequency motor direction controlled based on DTMF technology is explained in this article. Here is a circuit that operates the motor without using a microcontroller. This circuit consists of simple ICs.

When a key is pressed from our mobile, it generates a tone combination of two frequencies from our keypad. In the two frequencies, one is high frequency and another one is low frequency. This frequency can be decoded by the decoder IC into binary sequence.




DTMF based motor direction controlledcircuit consists of DTMF decoder IC, driver IC l293D IC and motors.

DTMF decoder IC used is HT9107B. It has 18 pins. Tone from DTMF encoder is given to the DTMF decoder IC. The decoder IC internally, consists of operational amplifier whose output is given to pre filters to separate low and high frequencies. Then it is passed to code detector circuit and it decodes the incoming tone into 4bits of binary data. This data at the output is directly given to the driver IC to drive the two motors. These motors rotate according to the decoded output.

If the button pressed from mobile is ‘1’, it gives a decoded output of ‘0001’. Thus motor connected to the first two pins will get 0 volts and second motor will have 5 volts to one  pin and 0 volts to the another pin. Thus second motor starts rotating and first motor is off. So, robot moves in one direction either to left or right. If the robot is to rotate forward or backward then the binary value should be either ‘0101’ or ‘1010’.These values indicate that two motors rotates in the same direction i.e. either forward or backward. The following table gives the low frequency, high frequency and binary output value of each button pressed in the keypad.


DTMF Decoded Frequency Output Table

Circuit Components:

  • DTMF Decoder IC (HT9107B)
  • Motor Driver IC L293d
  • Motors 100rpm/6volt
  • Resistors – R1=100k, R2=100k& R3=330k
  • Capacitors – C1 =C4=100nf, C2=C3=22uf
  • Crystal =3.58mhz
  • Mobile jack

How DTMF based Motor direction controlled Circuit Works?

  • Arrange the circuit mechanically i.e. connect the wheels to the motors, place the circuit on the mobile fixed to it.
  • Now press ‘5’ from your mobile, starts moving forward direction of motor.
  • Now press ‘0’ from your mobile, robot starts moving backwarddirection of motor.


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Software Requirement :   Dip Trace, Tina Pro

Hardware Requirement :   Mobile, IC-HT9107B, L293D, Motor

Application :  

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