Circuit descriptionThe entire hardware circuit of safety guard
for blind is divided into four major sections. i.e. transmitter,
receiver, switching section, and the voice processing
section.Transmitter section:-The logic of this section is simple
and is built around most versatile IC NE555 (IC1), configured as
astable multivibrator to produce frequency about 38 KHz. This is
so, because IR module receiver used here works in range of 38 KHz
frequency. Timing component of this circuit is resistor VR1and
R1and capacitor C2, determine the range of oscillating. Where,
formula of generated frequency (F) from transmitter section is
given byF = 1.443 / (R1+ 2R2) C2The output frequency from pin 3 of
IC1is fed to base of transistor T1through resistor R3. Transistor
T1is configured as Darlington pair with transistor T2in order to
drive pair of IR LED connected in series as shown in figure 2.
LED1is used as transmitted signal indicator and resistor R5is used
as current limiter.
Receiver section:-When transmitted signal from transmitter is
obstructed by any object lies in its path then the transmitted
signal is reflected. The reflected signal is received by IR
receiver module (TSOP1738) and is fed to base NPN transistor
T3through resistor R6for amplification. Amplified signal is again
amplified by pair of transistor T4and T5up to necessary level. The
output from emitter of transistor T5is fed through resistor R13to
pin 2 (non-inverting input) of comparator (IC3) where inverting
input is connected to zener diode ZD1. The output is taken from pin
7 and is fed to I/O port P1.0 of microcontroller AT89c51 (IC4). The
output of pin 7 of IC3goes high only when non-inverting input is
more the inverting input (2.2V).
PARTS LISTResistors (all -watt, ~+mn~ 5% Carbon unless stated
otherwise)
R1, R2, R9, = 1 KR3, R6, R11, R13= 22 R4= 47 R5, R7= 100 R8= 15
R10= 68 R12= 4.7 KR14, R15, R16= 470 R17a= 620 R17b, R22, R23= 100
KR24= 5.1 KR26, R27= 10 KVR1= 2K (preset)VR2= 4.7 K (preset)
Capacitors
C1, C4= 100 F/25V (electrolytic)C2, C3= 0.01 F (ceramic disc)C5,
C6= 33 pF (ceramic disc)C7= 0.001 F (ceramic disc)C8, C14= 4.7
F/16V (electrolytic)C9, C10, C11, C13= 0.1 F (ceramic disc)C12= 220
F/16V (electrolytic)
Semiconductors
IC1= NE555 (timer IC)IC2= LM7805 (+5 Volt regulator)IC3= LM311
(comparator)T1, T2, T3, T4, T5= BC548 (NPN transistor)T6= BC558
(PNP transistor)ZD1= 2.2 volt, 1/4 watt (zener diode)D1= 1N4001
(rectifier diode)IR LED1, IR LED2= Infrared LED (5 mm
diameter)IRX1= TSOP1738 (IR receiver module)LED1, LED2, LED5= Red
LED (5 mm diameter)LED3= Green LED (5 mm diameter)LED4= Yellow LED
(5 mm diameter)
Miscellaneous
B1, B2= 9 Volt (battery)SW1, SW2= ON/OFF SPST (Single Pole
Single Throw) switchSW3, SW4= Push-To-On switch
