Coin Battery Operated Radio
This project is a one Transistor radio which uses a coin battery as a power supply!
The coin battery is described in project The Coin battery in Electric power section. You will want to experiment with different metals for your coin battery as well as different antennas and Antenna connections.
The test to determine the effectiveness of the coin battery is simple: compare the results when using the coin battery to the results when the coin battery leads are shorted together.
When experimenting with antennas, try both Antenna connections. The 10pF one generally works best with short Antennas. Try operation with and without a Ground connection, also. Sometimes the results are better without the Ground connection.
The transistor is operating as both the detector and audio amplifier. Detection is obtained by the non-linear (rectifying) characteristics or the B-E junction (base-emitter). The 220K Resistor supplies a small amount of initial base current to turn the Transistor ON. As radio signals are detected, the Transistor is turned ON harder.
This in turn causes more collector current and more loading on the battery. Strong stations may cause such a high loading on the coin battery that its voltage is decreased to the point where distortion is evident. Decrease antenna pick up to reduce this kind of distortion. You can also use this radio with the 3V Battery or even a 1.5V cell if you like. Have fun!