.......This phut-phut sounds like that of an idling engine. Now lfor throt-
V tling, turn the potentiometer gradually so that an increase inthe rate
of phut-phut is obtained.
The heart of the unit is a free running multivibrator. The fre
quency ofthe multivibrator is adjusted by the potentiometer, which
in turn produces the throttling effect. The ‘start’ push button con-
nects the supply across the condenser and when pressed, charges the
condenser to the supply voltage. The charge stored in the condenser
is sufficient to operate the unit for a few seconds after which it dis-
charges. This results
giving an effect of that of a starting engine. On switching the ON!
OFF switch to ‘on’ position, the power supply gets connected to the
unit; continuous low frequency phut-phut notes are produced which
indicate that the engine has started and now is idling. In order to
4 accelerate the engine, rotate the potentiometer knob. With the
decrease in resistance the phut-phut rate indreases. For stopping/}the
motor boat engine, switch off the power supply (ON/OFF switch).
The motor phut-phut then gradually dies oi?. The coupling capacitor
connected in series with the output prevents the DC from flowing
through it but lcts thc pulsc to pass through it. Thcvconncctions of
fha switches are also SHOWN IN THE FIG..
Parts Required for building this electronic boat sound effect generator circuit:
1. Transistors : AC 128 ><2 Nos.
2. Coudenscrs : 500 mfd 6 volts 1 No.
1000 mfd 6 volts-1No.
2 mfd 6 volts 2 Nos.
0.22 mfd >< 50 volts 1 No.
3. Resistanccs : (:1; watt)
1 K 2 Nos.
( – 10 K 2 Nos. _
68 K 1 No.
4. Potcntiomctcr; 100 K Lin. 1 N0.
5. Diode : ISM]
6. K Stcp down transformer : 3 volts 100 mA.
7. Push-on switch : ON/OFF switch.