
Make a grooving on the top of the plastic bottle and fix a straw in the hole in such a way that a portion of straw is present on the top, while the rest part of the straw lies inside the bottle. Attach four bottle caps to the ends of the straws with the help of glue. Cut a straw in half, insert both the straw pieces into the pair of grooves. First of all, place the bottle horizontally on the table and make two pairs of grooves on the curved surface of the bottle near the opening and the base. The main items required to make a balloon car include one plastic bottle, two straws, four bottle caps, one balloon, and glue.

The values of two capacitors C1 and C2 decide the feedback amount. The amplified signal is supplied to the tank circuit to meet out losses during the conversion of energy between the two capacitors and inductors. These oscillations at C2 are applied to the transistor base-emitter terminal which amplifies it and is obtained at the collector terminal.

When the power supply is provided to the circuit, both the capacitors C1 and C2 get charged and then discharge through the inductor which initially produces oscillations. The transistor BC547 works as an emitter follower where R1 and R2 resistors bias the CB (collector-base) terminals and BE (base-emitter) terminals while the collector and base terminals have a tank circuit in their feedback path. The inductor is connected in parallel to the series capacitors C1 and C2 (tapped capacitors). The Colpitts oscillator circuit contains only a few components arranged in the following order.
