radio-keychain

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!

Motivation

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.

How to use

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!

Schematic and PCB

https://kicanvas.org/?repo=https://github.com/alx-alexpark/radio-keychain

Zine

Bill of Materials

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