VEGAKIT
(14ELECTRONIC CAR HORN (TBA 810+555)
This project describes the Modulation of the master tone capacitors C12.
constructional and working is governedby IC1,which runs
details of an electronic at 1Hz. the frequency fixing cONSTRUCTION
horn.primarily designed for components are R1,R2 and During assembly of the com-
cars. It can however also be C1. With the values used for ponents, extrem are should be
used effectively as a novel R1 and R2 almostequal mark taker for the polarities or
door-bell. space ratio (square wave) is electrolytics and semiconduc-
The horn presented here is of obtained at pin 3. tors. IC socket are recom-
2-note (modulated sound) mended for IC1 and IC2. IC3
type and delivers about 4w Coupling between IC1 and may be soldered directly on
musical power at 12volt. IC2 is provided by capacitor the PCB and over the T03
While using it as a call bell, C3,IC1 connects capacitor Power transistor type cooling
6VDC supply is enough. C3inparallel to C4 during the lip should be clamped. Be-
Which can be derived either 'on' period and disconnects it fore soldering IC3,its pin
from dry battery cells or a bat-
during the 'off' period. Value should be straightened so
tery eliminator. The systemsof C3 is so chosen that when that they fall in straight lines,as
is flexible enough to work it is connected in parallel to in a DIL type IC The cooling
offright from 6V to 18V sup-
C4 through IC1,the output of tab of IC3 should also be
Ply, Ic2 is around 200 Hz Since pulled slightly upwords, so
without change of any com- IC1 is runhing at 1 Hz,the re- that it forms a good electrical
ponents in the circuitry. sultant output of IC2 is 400Hz contact with the colling clip
However,it is important to use for half second and 200 Hz for above it. A bit of heatsink
a speaker of the jright rating. the next half second and so compound pay be applied on
The speaker should be rated on. the top of IC3 to reduce the
one watt for 6V,5watt for 12V thermal resistance between
and 7watt for 18V. Capacitors C2 and C3 are IC and the cooling lip.
the functional components for
Circuit IC1 and IC2. Modulate 1 out After wiring the circuit com-
The circuit works around three put of IC2, available at its pin pletely and checking it up thor-
ICs. While IC1 and IC2 are 3 is attenuated through the oughly, connect the card to
fortone generation, IC3 works potential divider comprising 12V DC supply, giving due
as power amplifier. Supply to R5 and R6 and fed to the care to the polarities and
the system is derived from amlifier through capacitor measures the voltages en-
12V car battery and fed di- C6. Power amplifier is circled at various points. If the
rectly to IC3,IC1 and Ic2 re- formed around IC3 and the voltages are quite near the
ceive the regulated supply of components around that 1C values shown, connect a rated
5.1volt derived through zener are its functional components. loudspeaker across output
D1 and resistor R7. terminals. You are sure to
While R9 fixes the input sen- hear the modulated horn.
The master tone of approx. sitivity, C10 and C11 fix the Slight changes in note and
400 Hz generated by IC2 is frequency response of the rhythm can be afffected by
fixed by R3, R4 and C4. The amplifier. Output of IC3 avail- varying the values of capaci-
ratio of R3 to R4 fixes the able at its pin 12 is fed to the tors C4 and C1 respectively,
softness'in the sound output. loudspeakerthrough coupling to suit the individual taste.
The module may be housed in one in on positlon and to PART LIST
in a suitable enclosure and fit- this electronic horn in the other
ted within the car's engine position. RESISTORS:
compartment (under the bon- R1 -1K
For using the horn as a door- R2.3.8 -100K
net, be
sufficiently away from the en- bell, the PCB may RA -4.7K
The mounted within the loud- R
gine and its heat. -10K
speaker can be mounted on speaker cover,together with R6 -470E
the engine ventilation gril from battery eliminator. Main sup- R7,10 -100E/1WATT
within. The negative supply is ply to the eliminator should be Ra -10E
to be given directly by screw- controlled through a bell-push
ing the negative lead of cord switch. You are thus sure to CAPACITORS :
to the car's metallic frame have a novel attraction for the C 4.7uF/6V
(assuming the car has a bat- vistors. C2,5 -01uF/50v
tery with its negative C3 022uF/50V
grounded). Whereas positive C4 -033uF/50V
supply may be given to it C6 4.7uF/6V
through the car's horn relay. C7 -470uF/16V
C8,9 -100uF/16V
In crowded areas. Such mu- C10 -1.5Kpf
sical horns become ineffec- C11 -5.6Kpf
tive. It is therfore suggested C12 -1000uF/25V
that a changeover switch may
beprovided in the dashboard, SEMICONDUCTORS
which would allow the positive IC1,1 -555
supply to the car's normal IC3 TBA 810S
horn D1 -5.1V/1N
MISC.
IC SOCKETS FOR IC1,2
SPEAKER
HEAT SINK FOR IC3
R7
-06 18V
R R3 RIO
2IC1 c3 IC2 T8A 2
65553HH 555
6
LS
