A fully-functional FM receiver in a 3x3cm footprint, perfect for a keychain.
It uses the connected headphones as an antenna, and is powered off a CR2032 coin cell. The FM tuner used is the Si4702, which supports the 76-108MHz frequency range.
Based on the CH32v003, this radio runs on RISC-V!
I love radio, and I wanted to make the tiniest keychain radio possible. I also thought it would be interesting to learn how radios work.
First, connect a pair of headphones or an aux cable, this is your antenna. There are 4 buttons on the device, a volume up/down, and a frequency up/down. First, set the volume to a confortable level, and then use the frequency up/down buttons to step up and down 0.1MHz until you find a station. Then, enjoy listening to the station!
https://kicanvas.org/?repo=https://github.com/alx-alexpark/radio-keychain
| Designator | Footprint | Quantity | Value | LCSC Part # |
|---|---|---|---|---|
| BT1 | BAT-SMD_MY-2032-12 | 1 | MY-2032-12 | C964833 |
| C1, C6 | 0402 | 2 | 100nF | C1525 |
| C2 | 0402 | 1 | 100pF | C1546 |
| C3, C4 | 0603 | 2 | 0.47uF | C1623 |
| C5, C7, C8 | 0603 | 3 | 1uF | C1592 |
| C9 | 0402 | 1 | 22nF | C1532 |
| CN1 | PJ-320D | 1 | PJ-320D | C431535 |
| D1 | 0402 | 1 | LED | C2286 |
| FB1, FB2 | 0603 | 2 | BLM18BD252SN1D | C77668 |
| J1 | PinHeader_1x03_P2.54mm_Vertical | 1 | Conn_01x03_Pin | — |
| L1 | 0603 | 1 | LQW18ANR27J00D | C98093 |
| OSC1 | CRYSTAL-SMD_4P-L3.2-W2.5-BL | 1 | SX2M32_768KM20F30TNN | C2901603 |
| R1, R2, R3, R4, R5, R6 | 0603 | 6 | 10k | C25804 |
| R10, R9 | 0402 | 2 | 2k | C4109 |
| R11 | 0402 | 1 | 330 | C25104 |
| R7, R8 | 0402 | 2 | 2.2k | C25879 |
| SW1, SW2, SW3, SW4 | SW-SMD_4P-L4.2-W3.3-P2.15-LS5.1 | 4 | SW_Push_45deg | C455282 |
| SW5 | SW-SMD_MST22D18G2 | 1 | K3-2235S-F1 | C223858 |
| U1 | QFN-20-1EP_3x3mm_P0.4mm_EP1.65x1.65mm | 1 | CH32V003F4U6 | C5299908 |
| U2 | QFN-28_4x4mm_P0.5mm | 1 | TPA6130A2RTJR | C130046 |
| U3 | MPS_QFN-16_3x3mm_P0.5mm | 1 | SI4702-C19-GMR | C2155666 |
