Conventionally, wireless-controlled robots use RF
circuits, which have the drawbacks of limited working range, limited
frequency range and limited control. Use of a mobile phone for
robotic control can overcome these limitations. It provides the
advantages of robust control, working range as large as the coverage
area of the service provider,no interference with other controllers and up
to twelve controls.
Although the appearance and capabilities of robots vary
vastly, all robots share the features of a mechanical, movable
structure under some form of control. The control of robot involves
three distinct phases: perception, processing and action. Generally,
the preceptors are sensors mounted on the robot, processing is done
by the on-board microcontroller or processor, and the task
(action) is performed using motors or with some other actuators.
Project overview:
In this project, the robot is controlled by a mobile
phone that makes a call to the mobile phone attached to the
robot. In the course of a call, if any button is pressed, a tone
corresponding to the button pressed is heard at the other end of the
call. This tone is called ‘dual-tone multiple-frequency’ (DTMF)
tone. The robot perceives this DTMF tone with the help of the phone
stacked in the robot.
The received tone is processed by the ATmega16
microcontroller with the help of DTMF decoder MT8870. The decoder
decodes the DTMF tone into its equivalent binary digit and this
binary number is sent to the microcontroller. The
microcontroller is preprogrammed to take a decision for
any given input and outputs its decision to motor drivers in
order to drive the motors for forward or backward motion or a
turn.
The mobile that makes a call to the mobile phone stacked
in the robot acts as a remote. So this simple robotic
project does not require the construction of receiver
and transmitter units.
DTMF signaling is used for telephone signaling over the
line in the voice- frequency band to the call switching
center. The version of DTMF used for telephone tone dialing is
known as ‘Touch-Tone.’
DTMF assigns a specific frequency (consisting of two
separate tones) to each key so that it can easily be identified
by the electronic circuit. The signal generated by the
DTMF encoder is a direct algebraic summation, in real time,
of the amplitudes of two sine (cosine) waves of different
frequencies, i.e., pressing ‘5’ will send a tone made by adding 1336
Hz and 770 Hz to the other end of the line. The tones and assignments
in a DTMF system are shown in Table I.
Circuit description:
Fig. 1 shows the block diagram of the microcontroller-based
mobile phone operated land rover. The important components of this
rover are a DTMF decoder, microcontroller and motor driver.
An MT8870 series DTMF decoder is used here. All types of the
MT8870 series use digital counting techniques to detect and decode
all the 16 DTMF tone pairs into a 4-bit code output. The built-in
dial tone rejection circuit eliminates the need for pre-filtering.
When the input signal given at pin 2 (IN-) in single-ended input
configuration is recognized to be effective, the correct 4-bit decode
signal of the DTMF tone is transferred to Q1 (pin 11) through Q4 (pin
14) outputs.
Table II shows the DTMF data output table of MT8870. Q1
through Q4 outputs of the DTMF decoder (IC1) are connected to port
pins PA0 through PA3 of ATmega16 microcontroller (IC2) after
inversion by N1 through N4, respectively.
The ATmega16 is a low-power, 8-bit, CMOS microcontroller
based on the AVR enhanced RISC architecture. It provides the
following features: 16 kB of in-system programmable Flash
program memory with read-while-write capabilities, 512 bytes of
EEPROM, 1kB SRAM, 32 general-purpose input/output (I/O) lines and 32
general-purpose working registers. All the 32 registers are directly
connected to the arithmetic logic unit, allowing two
independent registers to be accessed in one single instruction
executed in one clock cycle. The resulting architecture is
more code-efficient.
Outputs from port pins PD0 through PD3 and PD7 of the
microcontroller are fed to inputs IN1 through IN4 and enable pins
(EN1 and EN2) of motor driver L293D, respectively, to drive two
geared DC motors. Switch S1 is used for manual reset. The
microcontroller output is not sufficient to drive the DC motors, so
current drivers are required for motor rotation.
The L293D is a quad, high-current, half-H driver designed to
provide bidirectional drive currents of up to 600 mA at voltages from
4.5V to 36V. It makes it easier to drive the DC motors. The L293D
consists of four drivers. Pins IN1 through IN4 and OUT1 through OUT4
are input and output pins, respectively, of driver 1 through
driver 4. Drivers 1 and 2, and drivers 3 and 4 are enabled by
enable pin 1 (EN1) and pin 9 (EN2), respectively. When enable input
EN1 (pin 1) is high, drivers 1 and 2 are enabled and the outputs
corresponding to their inputs are active. Similarly, enable input EN2
(pin 9) enables drivers 3 and 4.
Software description:
The software is written in ‘C’ language and compiled using
CodeVision AVR ‘C’ compiler. The source program is converted into hex
code by the compiler. Burn this hex code into ATmega16 AVR
microcontroller.
The source program is well commented and easy to understand.
First include the register name defined specifically for ATmega16 and
also declare the variable. Set port A as the input and port D as the
output. The program will run forever by using ‘while’ loop. Under
‘while’ loop, read port A and test the received input using ‘switch’ statement.
The corresponding data will output at port D after testing of
the received data.
Working:
In order to control the robot, you need to make a call to the
cell phone attached to the robot (through head phone) from any phone,
which sends DTMF tunes on pressing the numeric buttons. The cell
phone in the robot is kept in ‘auto answer’ mode. (If the mobile does
not have the auto answering facility, receive the call by ‘OK’ key on
the rover-connected mobile and then made it in hands-free mode.) So
after a ring, the cellphone accepts the call.
Now you may press any button on your mobile to perform
actions as listed in Table III. The DTMF tones thus produced are
received by the cellphone in the robot. These tones are fed to the
circuit by the headset of the cellphone. The MT8870 decodes
the received tone and sends the equivalent binary number to the
microcontroller. According to the program in the microcontroller, the
robot starts moving.
When you press key ‘2’ (binary equivalent 00000010) on
your mobile phone, the microcontroller outputs ‘10001001’ binary
equivalent. Port pins PD0, PD3 and PD7 are high. The high output at
PD7 of the microcontroller drives the motor driver (L293D). Port pins
PD0 and PD3 drive motors M1 and M2 in forward direction (as per Table
III). Similarly, motors M1 and M2 move for left turn, right turn,
backward motion and stop condition as per Table III.
Construction:
When constructing any robot, one major mechanical constraint
is the number of motors being used. You can have either a two-wheel
drive or a four-wheel drive. Though four-wheel drive is more complex
than two-wheel drive, it provides more torque and good
control. Two-wheel drive, on the other hand, is very easy to construct.
Top view of a four-wheel-driven land rover is shown in Fig.
3. The chassis used in this model is a 10×18cm2 sheet made up of
parax. Motors are fixed to the bottom of this sheet and the circuit
is affixed firmly on top of the sheet. A cellphone is also mounted on
the sheet as shown in the picture.
In the four-wheel drive system, the two motors on a side are
controlled in parallel. So a single L293D driver IC can drive the
rover. For this robot, beads affixed with glue act as support wheels.
Tip and Ring:
Most of the readers cant pass this term 'Tip' and 'Ring'; so for
your convenience lets try to solve this. First of all identify the tip and ring
with the help of the figure, given below, then use the DMM and apply the short
circuit test to know the unknown wires.
For short circuit test select the 'buzzer' sign in the DMM then
connect the one lead tip and the other with the hand frees cut wires one by
one, when you hear the beep you got it! that is you wire, the tip wire.
Similarly, now connect the DMM lead to ring the other with the rest of the
wires and do the same. Cut the hand frees wire before the mike. I hope it ll
work for you guys.
Component Required:
IC1 -
MT8870 DTMF decoder
IC2 -
ATmega16 AVR microcontroller
IC3 -
L293D motor driver
IC4 -
74LS04 NOT gate
D1 -
1N4007 rectifier diode
R1, R2 -
100-kilo-ohm
R3 -
330-kilo-ohm
R4-R8 -
10-kilo-ohm
C1 -
0.47μF ceramic disk
C2, C3, C5, C6 - 22pF ceramic disk
C4 -
0.1μF ceramic disk
XTAL1 -
3.57MHz crystal
XTAL2 - 12MHz
crystal
S1 -
Push-to-on switch
M1, M2 - 6V,
50-rpm geared DC motor
Batt. -
6V, 4.5Ah battery
