1. Construction
Cellphone-Operated
Land Rover
 P Raghavendra PRASAD and
. no interference with other controllers Parts List
K. Susram Rahul and up to twelve controls.
Semiconductors:
Although the appearance and
C
IC1 - MT8870 DTMF decoder
onventionally, wireless-con- capabilities of robots vary vastly, IC2 - ATmega16 AVR
trolled robots use RF circuits, all robots share the features of a me- microcontroller
which have the drawbacks of chanical, movable structure under IC3 - L293D motor driver
IC4 - 74LS04 NOT gate
limited working range, limited fre- some form of control. The control of
D1 - 1N4007 rectifier diode
quency range and limited control. Use robot involves three distinct phases:
of a mobile phone for robotic control preception, processing and action. Resistors (all ¼-watt, ±5% carbon):
R1, R2 - 100-kilo-ohm
can overcome these limitations. It Generally, the preceptors are sensors R3 - 330-kilo-ohm
provides the advantages of robust mounted on the robot, processing is R4-R8 - 10-kilo-ohm
control, working range as large as the done by the on-board microcontrol-
Capacitors:
coverage area of the service provider, ler or processor, and the task (action) C1 - 0.47µF ceramic disk
is performed using C2, C3, C5, C6 - 22pF ceramic disk
motors or with some C4 - 0.1µF ceramic disk
other actuators. Miscellaneous:
XTAL1 - 3.57MHz crystal
Project XTAL2 - 12MHz crystal
overview S1 - Push-to-on switch
M1, M2 - 6V, 50-rpm geared
In this project, the DC motor
robot is controlled Batt. - 6V, 4.5Ah battery
by a mobile phone
that makes a call to a tone corresponding to the button
the mobile phone at- pressed is heard at the other end of
tached to the robot. In the call. This tone is called ‘dual-tone
the course of a call, if multiple-frequency’ (DTMF) tone.
Fig. 1: Block diagram of cellphone-operated land rover any button is pressed, The robot perceives this DTMF tone
Fig. 2: Circuit diagram of microcontroller-based cellphone-operated land rover
6 2 • j u ly 2 0 0 8 • e l e c t ro n i c s f o r yo u w w w. e f y m ag . co m

2. Construction
with the help of the phone stacked in decoder decodes the DTMF
the robot. tone into its equivalent bi-
The received tone is processed by nary digit and this binary
the ATmega16 microcontroller with the number is sent to the micro-
help of DTMF decoder MT8870. The controller. The microcontrol-
ler is preprogrammed to
Table I take a decision for any
Tones and Assignments given input and out-
in a DTMF System puts its decision to motor
Frequencies 1209 Hz 1336 Hz 1477 Hz 1633 Hz drivers in order to drive
the motors for forward
697 Hz 1 2 3 A
or backward motion or
770 Hz 4 5 6 B
a turn.
852 Hz 7 8 9 C T h e m o b i l e t h a t Fig. 3: Top view of the land rover
941 Hz * 0 # D makes a call to the mo-
bile phone stacked in the gebraic summation, in real time, of
Table II robot acts as a remote. So the amplitudes of two sine (cosine)
DTMF Data Output this simple robotic project waves of different frequencies, i.e.,
does not require the con- pressing ‘5’ will send a tone made
Low High Digit OE D3 D2 D1 D0
group (Hz) group (Hz) struction of receiver and by adding 1336 Hz and 770 Hz to the
transmitter units. other end of the line. The tones and
697 1209 1 H L L L H
DTMF signaling is assignments in a DTMF system are
697 1336 2 H L L H L
used for telephone sign- shown in Table I.
697 1477 3 H L L H H aling over the line in the
770 1209 4 H L H L L voice-frequency band to Circuit description
770 1336 5 H L H L H the call switching centre. Fig. 1 shows the block diagram of the
770 1477 6 H L H H L The version of DTMF microcontroller-based mobile phone-
852 1209 7 H L H H H used for telephone tone operated land rover. The important
852 1336 8 H H L L L dialing is known as components of this rover are a DTMF
852 1477 9 H H L L H ‘Touch-Tone.’ decoder, microcontroller and motor
941 1336 0 H H L H L DTMF assigns a spe- driver.
941 1209 * H H L H H cific frequency (con- An MT8870 series DTMF decoder
941 1477 # H H H L L sisting of two separate is used here. All types of the MT8870
tones) to each key so series use digital counting techniques
697 1633 A H H H L H
that it can easily be to detect and decode all the 16 DTMF
770 1633 B H H H H L
identified by the elec- tone pairs into a 4-bit code output. The
852 1633 C H H H H H
tronic circuit. The signal built-in dial tone rejection circuit elimi-
941 1633 D H L L L L
generated by the DTMF nates the need for pre-filtering. When
— — ANY L Z Z Z Z encoder is a direct al- the input signal given at pin 2 (IN-) in
single-ended input configuration is
Table III recognised to be effective, the correct
4-bit decode signal of the DTMF tone is
Actions Performed Corresponding to the Keys Pressed
transferred to Q1 (pin 11) through Q4
Number Output of HT9170 Input to the Output from Action (pin 14) outputs.
pressed DTMF decoder microcontroller microcontroller performed
Table II shows the DTMF data
by user
output table of MT8870. Q1 through
2 0×02 0×FD 0×89 Forward motion Q4 outputs of the DTMF decoder (IC1)
00000010 11111101 10001001
are connected to port pins PA0 through
4 0×04 0XFB 0×85 Left turn
PA3 of ATmega16 microcontroller
00000100 11111011 10000101 Right motor forwarded
Left motor backwarded (IC2) after inversion by N1 through N4,
6 0×06 0XF9 0×8A Right turn respectively.
00000110 11111001 10001010 Right motor backwarded The ATmega16 is a low-power,
Left motor forwarded 8-bit, CMOS microcontroller based on
8 0×08 0XF7 0×86 Backward motion the AVR enhanced RISC architecture. It
00001000 11110111 10000110 provides the following features: 16 kB
5 0×05 0XFA 0×00 Stop of in-system programmable Flash pro-
00000101 11111010 00000000 gram memory with read-while-write
w w w. e f y m ag . co m e l e c t ro n i c s f o r yo u • j u ly 2 0 0 8 • 6 3

3. Construction
Fig. 4: An actual-size, single-side PCB layout for cellphone-operated land rover Fig. 5: Component layout for the PCB
capabilities, 512 bytes of EEPROM, 1kB their inputs are active. Similarly, en- mobile does not have the auto answer-
SRAM, 32 general-purpose input/out- able input EN2 (pin 9) enables drivers ing facility, receive the call by ‘OK’
put (I/O) lines and 32 general-purpose 3 and 4. key on the rover-connected mobile
working registers. All the 32 registers An actual-size, single-side PCB and then made it in hands-free mode.)
are directly connected to the arithmetic for cellphone-operated land rover is So after a ring, the cellphone accepts
logic unit, allowing two independent shown in Fig. 4 and its component the call.
registers to be accessed in one single layout in Fig. 5. Now you may press any button
instruction executed in one clock cy- on your mobile to perform actions as
cle. The resulting architecture is more Software description listed in Table III. The DTMF tones
code-efficient. The software is written in ‘C’ language thus produced are received by the
Outputs from port pins PD0 and compiled using CodeVision AVR cellphone in the robot. These tones are
through PD3 and PD7 of the mi- ‘C’ compiler. The source program is fed to the circuit by the headset of the
crocontroller are fed to inputs IN1 converted into hex code by the compil- cellphone. The MT8870 decodes the
through IN4 and enable pins (EN1 er. Burn this hex code into ATmega16 received tone and sends the equiva-
and EN2) of motor driver L293D, AVR microcontroller. lent binary number to the microcon-
respectively, to drive two geared DC The source program is well com- troller. According to the program in
motors. Switch S1 is used for manual mented and easy to understand. First the microcontroller, the robot starts
reset. The microcontroller output is include the register name defined spe- moving.
not sufficient to drive the DC motors, cifically for ATmega16 and also declare When you press key ‘2’ (bi-
so current drivers are required for mo- the variable. Set port A as the input nary equivalent 00000010) on your
tor rotation. and port D as the output. The program mobile phone, the microcontroller
The L293D is a quad, high-cur- will run forever by using ‘while’ loop. outputs ‘10001001’ binary equiva-
rent, half-H driver designed to pro- Under ‘while’ loop, read port A and lent. Port pins PD0, PD3 and PD7
vide bidirectional drive currents of test the received input using ‘switch’ are high. The high output at PD7 of
up to 600 mA at voltages from 4.5V to statement. The corresponding data the microcontroller drives the motor
36V. It makes it easier to drive the DC will output at port D after testing of the driver (L293D). Port pins PD0 and
motors. The L293D consists of four received data. PD3 drive motors M1 and M2 in
drivers. Pins IN1 through IN4 and forward direction (as per Table III).
OUT1 through OUT4 are input and Working Similarly, motors M1 and M2 move
output pins, respectively, of driver 1 In order to control the robot, you for left turn, right turn, backward
through driver 4. Drivers 1 and 2, and need to make a call to the cell phone motion and stop condition as per
drivers 3 and 4 are enabled by enable attached to the robot (through head Table III.
pin 1 (EN1) and pin 9 (EN2), respec- phone) from any phone, which sends
tively. When enable input EN1 (pin DTMF tunes on pressing the numeric Construction
1) is high, drivers 1 and 2 are enabled buttons. The cell phone in the robot When constructing any robot, one ma-
and the outputs corresponding to is kept in ‘auto answer’ mode. (If the jor mechanical constraint is the number
6 4 • j u ly 2 0 0 8 • e l e c t ro n i c s f o r yo u w w w. e f y m ag . co m

4. Construction
of motors being used. You can have ei- Motors are fixed to the bottom of this Further applications
ther a two-wheel drive or a four-wheel sheet and the circuit is affixed firmly This land rover can be further im-
drive. Though four-wheel drive is more on top of the sheet. A cellphone is also proved to serve specific purposes. It
complex than two-wheel drive, it pro- mounted on the sheet as shown in the requires four controls to roam around.
vides more torque and good control. picture. The remaining eight controls can be
Two-wheel drive, on the other hand, is In the four-wheel drive system, configured to serve other purposes,
very easy to construct. the two motors on a side are control- with some modifications in the source
Top view of a four-wheel-driven led in parallel. So a single L293D program of the microcontroller.
land rover is shown in Fig. 3. The driver IC can drive the rover. For this Note. The source code of this arti-
chassis used in this model is a robot, beads affixed with glue act as cle has been included in this month’s
10×18cm2 sheet made up of parax. support wheels. EFY CD.
Robot.C
Source program: case 0x02: //if I/P is 0x02 }
Robit.c { case 0x06:
#include <mega16.h> PORTD=0x89;//O/P 0x89 ie Forward {
void main(void) break; PORTD=0x8A; // Right turn
{ } break;
unsigned int k, h; case 0x08: //if I/P is 0x08 }
DDRA=0x00; { case 0x05:
DDRD=0XFF; PORTD=0x86; //O/P 0x86 ie Backward {
while (1) break; PORTD=0x00; // Stop
{ } break;
k =~PINA; case 0x04: }
h=k & 0x0F; { }
switch (h) PORTD=0x85; // Left turn }
{ break; } 
6 6 • j u ly 2 0 0 8 • e l e c t ro n i c s f o r yo u w w w. e f y m ag . co m