How expandable is the GPIO pin set for CM4? What good accesories and connectors are out there?

Was wondering this for the CM4 as there are 40 pins, but I couldnt find any accesories thst go from flat serial to rpi type bigger pins. Also, while reading DevTerms forums, there was a lot of disappointing talk of how most of the pins are already taken by the custom clockwork board.

J3 - 40 pin FPC header

GPIO 0 - 27
all clockwork cards us pins 0-5, and 8-11 to control the power, headphones, backlight, etc.
the remainder of these pins, 6-7 and 12-27 are not connected on the CM4 module.

MINI_PCIE - Ext Module

GPIO 28 - 45, Camera Pins, 2x USB, Speaker L/R
all of these pins are connected to the CM4 and A06, but using them requires a custom ext module board that will expose them.

Note these pin numbers are the common clockworkpi notation, they don’t map 1:1 with the CM4 pins.
I made a table yesterday, but haven’t double checked it yet, the numbers i mention above are the SODIMM GPIO numbers.

Pin/GPIO #
CM4 SODIMM Connection Purpose
2 2 PMU_IRQ Power
3 3 WL_REG_ON Unused, to keep Wifi module off
4 4 WL_HOST_WAKE Unused, to keep Wifi module off
5 5 BT_REG_ON Unused, to keep BT module off
6 38 EXT MOD
7 39 EXT MOD
8 8 LCD_RESET Display
9 9 BL_CTRL Display
10 10 HP_DET Audio
11 11 PA_EN Audio
12 12 AUD_PWM0 Audio
13 13 AUD_PWM1 Audio
14 32 EXT MOD
15 33 EXT MOD 4g Module, RESET_MCU
16 40 EXT MOD
17 41 EXT MOD
18 28 EXT MOD
19 29 EXT MOD
20 30 EXT MOD
21 31 EXT MOD
22 IGPIO0 PWR_ON Power
24 34 EXT MOD 4G Module, POWER_MCU
25 35 EXT MOD
26 36 EXT MOD
27 37 EXT MOD
28 43 EXT MOD

nice work! amazing detective work - I’m still leaning toward linking by wifi to external devices via esp32… although some in the group are designing an Ext module that will have more USB ports similar to the DevTerm.

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I wonder if you know whether any of the pads on the default expansion board are actually routed to pcie? I noted from the uPico schematics that SCL/SDA (I2C) seem to be on pins 50/52 of the mini pcie connector. I’m hoping those 52 pins are available on the pads (middle in the picture). Any ideas?

Also, that’s not PCIe, just a board-to-board connector using the same connector with mini PCIe…

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Ok, so the ‘default’ expansion board I have is an unpopulated 4G card. The schematic then assumes a SIM7600G-H in the middle? UART, speakers, SIM USB that’s all clear. From it does look like it’s that layout. So, it could be ‘abused’.

Ah, found a layout: page 11