Homemade simplest radio

Single chip microcontroller STM32L151CCU6

0201 package SLP0603 ESD electrostatic diode 5V one-way ESD protection diode

Homemade Simplest Radio

(1) Structure:
On the front of the baseboard, there are three knobs. The left knob is a 365pf air variable capacitor, used for tuning. The middle one is a splitter for the old ore machine, featuring 8 lugs for switching the 8 taps of the tuning coil to achieve impedance matching with the detection input, thereby maximizing the detection output. The right knob is another 365pf air variable capacitor, used to adjust the resonant frequency of the frame coil. The frame coil is made from a glass tube with a diameter of 46mm and a length of 120mm (basically equivalent to an air-core coil, with minimal electromagnetic wave loss). Around this tube, 0.09*32 strands of enamelled wire are wound. Adjacent to the tuning coil is the antenna coil, without any gap between them. The winding of the tuning coil begins approximately 20 turns from the ground. A tap is drawn every 10 turns, totaling 8 taps, which will later be connected to the splitter. The antenna coil consists of 40 turns, 20 turns, and 30 turns respectively. The main contact of the splitter is connected to the end of the active ore, equivalent to the anode of the diode. Above the frame antenna, there are three arms measuring 600mm in length, while the lower arm measures 650mm in length. The longer arms are used to fix the structure onto the base. The upper three arms have 18 lower slots, and the lower arm has 19 lower trunk slots. During winding, the process starts from the lower arm near the middle lower slot. The wire used is 0.09*42 goose silk, wound around 18 turns and 1/4 turn, with the tail end fixed below the last slot in the arm. The active ore is of my own design (previously published in the production method). It has a larger head and looks very beautiful. Behind it is a transformer used to match the horn Speaker. The speaker is a 5W, 8-ohm model. During testing, it is connected to the double-pressure detection form, then connected to the half-wave detector. No difference in feel was observed compared to full-wave detection. Ultimately, to achieve the best effect, each 2AP9 and active ore were connected in parallel, allowing them to be converted into each other. Two output terminals are designed: one for high-impedance headphones, located on the left side behind the baseboard; the other is connected to the primary side of the transformer (impedance matcher), and the second is connected to the horn speaker. Both output terminals are equipped with a detection device, each having various filter capacitors. The transformer is also the original self-made power transformer, once used for 220V input and 10V*2 output, double-wire winding. The 220V side is connected to the detection output, while the two outputs are connected to the horn speaker. The horn speaker is a 5W, 8-ohm model. Each connection is evenly connected with a 1mm thick enamelled wire. (2) Effect:
In a quiet and safe environment, only one ground wire is connected (I am connected to the heating device). Within 4 meters, sound can be heard clearly. When an external antenna is connected (I am connected to the cable TV shielded online), sound can be heard within 5 meters. This radio is highly efficient. It is one of my favorite projects.