Solar Bug

Hide this solar-powered circuit
suitably and see the reaction
of your friends to the chirpy
sound produced by it every few minutes.
In all probability, it will coax
them to find out where the sound is
coming from.
The circuit runs off a miniature solar
power panel, which can be taken
out from an old calculator such as Citizen
CT-500. A panel giving 1.5V to
2.5V is required. Note that the circuit
can work properly from a panel as
small as 3 cm2.
If a digital voltmeter is connected
across capacitor C2, a slow build-up
of voltage can be observed when the
panel is exposed to light. Transistors
T1 and T2 form a relaxation oscillator.
When C1 charges to 0.6V, transistor
T1 conducts and the charge built up
in C2 is discharged through the
piezobuzzer to produce a short beep.
While testing the circuit, the value
of resistor R1 can be reduced to, say, 1
kilo-ohm. Use a good-quality buzzer
to ensure that the sound produced is
loud enough.