Engineer Ivan Kuleshov has shown off an ultra-minimal carrier board for the Raspberry Pi Compute Module 4 system-on-module, connecting to just one of the two high-density ports on its rear: the MinCab.
Launched late last year, the Raspberry PI Compute Module 4 and Compute Module 4 Lite — the latter lacking the eMMC storage of the former — offer performance equivalent to a Raspberry Pi 4 Model B single-board computer in a compact system-on-module form factor. Designed as a successor to the earlier Compute Module 3 range, the CM4 does away with the SODIMM edge connector in favour of two high-density connectors on the back — and, it transpires, you technically only need one.
At least, that's the approach taken by Iven Kuleshov for an ultra-minimal carrier board dubbed the MinCab, brought to our attention by CNX Software. Rather than connecting to both, the MinCab connects to the upper of the two high-density connectors in order to break out a USB Type-C connector for power and to provide access to 5V, 3.3V, ground, and eight general-purpose input/output (GPIO) pins with UART, I2C, PWM, and digital IO.
The idea, Kuleshov explains, is to create an easy and low-cost way of using a CM4 in smart home systems and other embedded projects — without having to go to the complexity, expense, and size of a full carrier board.
The design also leaves the second connector free for additional expansion, though with one caveat: Power would be required from the first connector, meaning the creation of what Kuleshov describes as a "an additional 'bridge' between boards" would be required — but this could be as simple as a wire running from board to board.