Faux Pi Zero

Open hardware RP2040 dev board in a Raspberry Pi Zero compatible form factor. Includes Mini HDMI (via bitbanged DVI) and microSD.

Description

This board aids with migrating a project from the Pi Zero to the RP2040 while retaining the option of moving back to the Pi Zero in the future. It has the same footprint as the Pi Zero and a partially compatible pinout, making it convenient to support both the RP2040 and Pi Zero in the same design.

Status

Works, but 1 of 2 boards received by JLCPCB had a solder bridge on the RP2040. Looking at JLCPCB's EasyEDA footprints, it looks like JLCPCB used longer pads for the RP2040. I'd recommend using a custom footprint and extending the pads, which hopefully will avoid defects.

A couple other things I'd change in retrospect:

• Expose UART TX/RX on the debug header and reorder pins so you can plug a picoprobe into the board w/o wires.
• Remove the hacky activity LED from the microSD since the lib already blinks GP25.
• Try for a 2 layer board to reduce cost
• Reduce buttons to 6 x 3.5 and maybe try to squeeze in an optional wireless module

DVI and microSD both appear to work with a basic test. I've exercised DVI, USB (host), SPI1, and the debug header quite a bit (all good). Other functionality is either lightly tested or untested.

Features

• Compatible footprint:
  • Mini HDMI (via bitbanged DVI)
  • Micro SD (via SPI mode. Cards must be <2TB)
  • Micro USB
  • Power (via Micro USB)
• Partially compatible pinout
• 16MB Flash
• Green status LED on GP25 (same as Pico)
• Red SD activity LED on GP9
• BOOTSEL and RESET buttons
• SWD Header

Pinout

See schematic for more details.

Mapping from Pi Zero to Faux Px Zero

Pi Pin	Pico Pin	Pi GPIO	Pico GP	Function	Notes
1, 17	36		3V3 (Out)
2, 4	39		VSYS
2, 4	40		VBUS
3	4	GPIO 02	GP 02	I2C_SDA
5	5	GPIO 03	GP 03	I2C_SCL
6, 9, 14, 20, 25, 30, 34, 39	3, 8, 13, 18, 23, 28, 33, 38, DBG-2		GND
7		GPIO 04	GP 24
8	1	GPIO 14	GP 00	UART0 TX
10	2	GPIO 15	GP 01	UART0 RX
11	12	GPIO 17	GP 09	SD_CSn	Can be used as GP with SD card removed. Note 10k pullup.
12	17	GPIO 18	GP 13	SPI1_CSn	Can be used to share SPI1 with SD card.
13	11	GPIO 27	GP 08	SD_DET	Can be used as GP with SD card removed.
15	14	GPIO 22	GP 10	DVI_CEC	DVI_CEC when JP3 closed. See schematic.
16	15	GPIO 23	GP 11
18	DBG-3	GPIO 24	SWD
19	6/10	GPIO 10	GP 04/07	SPI0_RX/TX	Select controller or peripheral via JP1 and JP2. See schematic.
21	10/6	GPIO 09	GP 07/04	SPI0_TX/RX	Select controller or peripheral via JP1 and JP2. See schematic.
22	DBG-1	GPIO 25	SWCLK
23	9	GPIO 11	GP 06	SPI0_SCLK
24	7	GPIO 08	GP 05	SPI0_CSn
26		GPIO 07
27	34	GPIO 00	GP 28	I2C_SCL	DVI_SDA when JP4 closed. See schematic.
28		GPIO 01	GP 29
29	31	GPIO 05	GP 26
31	32	GPIO 06	GP 27	I2C_SDA	DVI_SDA when JP5 closed. See schematic.
32		GPIO 12
33		GPIO 13
35	16	GPIO 19	GP 12	SPI1_RX / SD_DAT	Can be used as GP with SD card removed. Note 10k pullup.
36		GPIO 16	BOOTSEL
37	30	GPIO 26	RUN
38	20	GPIO 20	GP 15	SPI1_TX / SD_CMD	Can be used as GP with SD card removed.
40	19	GPIO 21	GP 14	SPI1_SCLK / SD_CLK	Can be used as GP with SD card removed.
		GP 23	DVI_D2+
	21	GP 16	DVI_CK-
	22	GP 17	DVI_CK+
	24	GP 18	DVI_D0-
	25	GP 19	DVI_D0+
	26	GP 20	DVI_D1-
	27	GP 21	DVI_D1+
	29	GP 22	DVI_D2-
35		N/C
37		3V3_EN
LED		GP 25

Schematic

(Click image to view PDF)