This crystal or galena radio uses a germanium diode. C1 is an old radio variable and L1 has 100 turns of 26 or 28 wire in a 1 inch PVC pipe. The antenna must be a long wire.
Found in a Popular Electronics from the 90s, this circuit uses thermistors for low noise...
The Buck-type DC-DC converter (voltage lowerer) shown in figure 11 is suggested by Analog Devices...
This 4-20 mA current interface was found on a 90's EDN. The components used are not common today and...