Progress_2_x - Engineering for Change

Soundless Horn

Source section

Astable

Multivibrator

•
The TSOP 1738(IR sensor) requires an incident
signal with a centre frequency of 38khz.

•
So the Infra red LED must be illuminated by a
signal that has a frequency of 38khz.

•
This is accomplished by generating the
required signal using an
atable

multivibrator
.


Source section

Advised data format

•
The main intricacy involved with the TSOP
1738 is that a continuous signal of 38khz is
treated as noise.

•
There is a suggested data format of sending IR
pulses to the sensor.

•
They should be in the form of bursts of cycles.

•
The bursts should have 10
-
70 cycles

Data format
(contd.,)

•
There should be a gap of at least 14 cycles
between the bursts.

•
While all these criteria being satisfied, the
frequency of the pulse train must be kept at
38khz.

Monostable

multivbrator

#2

•
As the format consists of bursts, to produce a
burst of cycles the
astable

should be on and
for the gap between the bursts it should be
off.

•
This can be achieved by drawing the
supply(
Vcc
) of the
astable

from the output of
the
monostable

multivibrator
.


Monostable

multivbrator

#2
(contd.,)

•
As there should be 10
-
70 cycles/burst based
on the frequency of the
astable

output signal
its time period can be calculated and hence
the time required for 20 cycles is determined.

•
This becomes the on time of the
monostable

multivibrator

#2.

•
Similarly based on the gap between the bursts
reqiured

the Off time should be adjusted.

Monostable

multivbrator

#1

•
This
multivibrator

forms the initial block of the
source section.

•
A driver while blowing a horn excites this
multivibrator
. This is nothing but the trigger to
the
multivibrator
.

•
It generates a signal that sustains for a
duration of 0.5 sec.

•
This forms the supply of the
monostable

#2.

Source section using Microcontroller

•
The circuit using
multivibrators

is only for
testing purpose

•
For accuracy and to reduce bulkiness, the same
can be implemented using Microcontroller