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Raspberry Pi CM4 carrier delivers isolated Modbus, 1-Wire, and CAN

Mar 5, 2021 — by Eric Brown — 9509 views

On Kickstarter: an open-spec, $120 “CM Hunter” carrier for the RPi CM4 with GbE, HDMI 2.0, 2x USB 2.0, micro-USB OTG, LCD, relay, and isolated RS485/Modbus, 1-Wire, and CAN.

The Raspberry Pi Compute Module carrier scene has always been interesting, as different companies focus on different applications. With its expanded feature set, the Raspberry Pi Compute Module 4 has spawned even more innovation in carriers that range from imaging to storage to robotics. The latest entry is a $99 Euro ($120) CM Hunter board that focuses on isolated industrial I/O.



CM Hunter with RPi CM4 and optional fan (left) and with optional touchscreen
(click images to enlarge)

The CM Hunter (which sounds like a good name for a cop show) is available on Kickstarter through Mar. 25, with shipments due in June. The all-or-nothing campaign has a long way to go to make its $15K goal. The board is being launched by Andreas Eberle, the head of Swiss embedded prototyping firm Quick Pick AG.

The CM Hunter supports all models in the Raspberry Pi CM4 line. The CM4 switches to dual (low speed and high speed) 100-pin connectors, enabling a smaller 55 x 40mm footprint than the CM3.

The $25 to $90 CM4 has the same Broadcom BCM2711 SoC with 4x 1.5GHz Cortex-A72 cores used by the Raspberry Pi 4. The CM4 ships with 2GB to 8GB LPDDR4-3200 RAM and 0GB to 32GB eMMC. There is a GbE controller with PoE support and optional 802.11ac with BT 5.0.

The 97 x 79mm CM Hunter is billed as an all-purpose industrial carrier that combines features that would otherwise require HATs. Unfortunately, there is no 40-pin GPIO connector so if the product mix is not right for you, you are out of luck.



CM Hunter block diagram (left) and closeup of space under CM4 with USB and CAN controllers
(click images to enlarge)

The CM Hunter provides RS485/Modbus, 1-Wire, and CAN 2.0B terminal plugs, as well as a 10Amps rated relay. The 4-layer PCB integrates GbE, HDMI 2.0, and 2x USB 2.0 ports. There is also a micro-USB OTG for 5V input, as well as a real-time clock and a microSD slot.

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An LCD connector supports optional 3.5- and 4-inch Raspberry Pi resistive touchscreens from Waveshare that stack on top. There is also an optional cooling fan. The board ships with a custom Raspbian (Raspberry Pi OS) stack with Python packages for Modbus, CAN, and 1-Wire.

The CM Hunter shares some traits with the recent, and similarly open-spec Tofu board, which is sold for $110 by another Swiss firm, Oratek. The Tofu boasts M.2 and micro-SIM slots to tap the CM4’s PCIe 2.0 interface.

Other RPi CM4 carriers with M.2 include Altium’s Gumstix Raspberry Pi CM4 Development Board and an upcoming Piunora carrier. There is also a $134 Over:Board Mini-ITX carrier that offers a full-size PCIe card.

Like the CM Hunter, most of the other CM4 carriers lack PCIe expansion. These include Sourcekit’s $14.50 PiTray mini, as well as other Gumstix carriers, including a Gumstix Raspberry Pi CM4 PoE Smart Camera board. There is also an upcoming Wiretrustee SATA Board for Raspberry Pi CM4 carrier.

Further information

The CM Hunter is available on Kickstarter through Mar. 25, with shipments due in June. More information may be found on the extensively detailed CM Hunter Kickstarter page.

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