Matchbox Radio – No Battery
A coil discovery that may be of use to fellow amateur radio builders.
The use of a 1000uH axial inductor enabled the building of a good performance tiny radio, fitting inside a small matchbox.
Solar cell powered and able to run from the light of a CFL desk lamp when indoors, the radio does suffer from some mains noise if next to the power cord (as in the video due to having only 1 hand free) but otherwise offers great reception of AM stations.
It is based around the TA7642 AM chip, which resembles a transistor.
The application datasheet shows a couple of transistors and other parts on the output section, so those had to be worked around. The output from Pin 3 now goes through a decoupling cap (1uf) and out to a crystal radio type telephone speaker.
Audio volume is perfectly adequate for general listening.
TA7642 AM chip
0.01uF ‘103’ capacitor
0.1uF ‘104’ capacitor
140pF variable capacitor
1.5V ‘calculator’ solar cell