Jumpers

This guide is applicable to the following device / devices:

TMU CM4

CAN-FD Pro

CAN-FD Pro +IP67 casing

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Overview

A jumper is a small electrical connector used to short two header pins on a PCB. When installed, it electrically connects the pins and changes the behavior of the circuit by enabling or disabling specific hardware functions.

On AutoPi devices, the jumper is used to override the Smart Power Manager (SPM) and force the internal Raspberry Pi compute module to receive a constant 5 V supply.

This configuration is primarily intended for:

• Developing firmware interacting with the SPM
• Debugging unexpected shutdowns or sleep events
• Running long development workloads
• Testing boot processes or system initialization
• Performing low-level hardware diagnostics.

Because this configuration bypasses the normal power management mechanisms, it should only be used for development purposes.

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Power Architecture Context

AutoPi devices receive power from the vehicle battery through the OBD-II interface. Under normal operation, power flows through the Smart Power Manager (SPM) before reaching the Raspberry Pi compute module.

Normal Power Path

Vehicle Battery -> Smart Power Manager (SPM) -> 5V Regulator -> Raspberry Pi Compute Module

The SPM is responsible for:

• Ignition state detection
• Sleep and wake transitions
• Battery protection
• Power state management.

Power Path with Jumper Installed

When the jumper is installed, the Smart Power Manager is bypassed:

Vehicle Battery -> 5V Regulator -> Raspberry Pi Compute Module

In this configuration, the Raspberry Pi receives constant power, independent of ignition state or SPM control logic.

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Installing the Jumper

To use a jumper, you will need to open up your AutoPi device. On the inside of the device, you'll see two boards connected to each other. One of them being the Raspberry Pi and the other - the AutoPi board. On the AutoPi board, you should be able to see two pins on one of the four corners, next to which is written 'FORCE 5V'.

To see how you can attach a jumper to your specific device view the following pages for:

• Generation 2 devices
• Generation 3 devices

The FORCE 5V jumper forces the device to maintain a constant 5 V supply to the Raspberry Pi compute module. Installing the jumper electrically bypasses the SPM power gating circuitry.

• Recommended - Use the jumper when:

  • SSH sessions are interrupted by device sleep.
  • Running long debugging sessions.
  • Developing new system services or kernel modules.
  • Investigating boot-time issues.

• Do not leave the jumper installed in production environments because:

  • Battery protection mechanisms are bypassed.
  • Sleep mode is disabled.
  • Vehicle battery drain may occur.

Required Component

A standard 2.54 mm (0.1 inch) jumper cap.

Locating the Jumper Pins

To locate the jumper pins:

1. Open the AutoPi enclosure.
2. Inside the enclosure there are typically two stacked boards:
   • Raspberry Pi Compute Module
   • AutoPi carrier board
3. Locate the two-pin header labeled FORCE 5V on the AutoPi board. Here is an example from our AutoPi CAN-FD Pro device installed inside the IP67 casing:

The exact location may vary slightly depending on device model.

Installation Procedure

1. Power off the AutoPi device.
2. Open the device enclosure.
3. Locate the header labeled FORCE 5V.
4. Place the jumper cap across the two pins.
5. Reassemble the enclosure.
6. Power the AutoPi device again.

Effects of Installing the Jumper

When the jumper is installed:

• Smart Power Manager power control is disabled.
• The Raspberry Pi receives continuous power.
• Automatic sleep and hibernation are disabled.
• Ignition signals no longer control the device power state.

This mode ensures the system remains powered during development or debugging sessions.

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Removing the Jumper

To restore normal power management behavior:

1. Power down the AutoPi device.
2. Remove the jumper cap.
3. Close the enclosure.
4. Reconnect power.

After removal, the Smart Power Manager will again control power states.

Side Effects

Because the SPM is bypassed, several protections and behaviors are disabled.

Potential side effects include:

• The device will not enter sleep mode.
• The device may drain the vehicle battery.
• Ignition state changes will not affect power state.

For this reason, the jumper should not be used in production deployments.

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Summary

Feature	Normal Mode	Jumper Installed
Smart Power Manager active	Yes	No
Sleep mode	Enabled	Disabled
Ignition control	Yes	No
Continuous power	No	Yes
Recommended for production	Yes	No

The FORCE 5V jumper is a hardware override that disables the Smart Power Manager and supplies constant power to the Raspberry Pi compute module. This mode is useful for development and debugging but should not be used during normal device operation.