MMR3 Powering through 5V connection ?

Hi there,

Please move this discussion if in the wrong section.

I was in discussion with one of your team members via email a few weeks ago about an issue not being able to use the new MMR3s on 5V alone. My understanding from these emails is that firmware 1.4.4 requires a Li-Po connected to the IMU, as compared to 1.3.8.

I have several MMR3s that have had their Li-Po's removed, and have been soldered onto PCBs. The IMU's only voltage in is a 5V supply into the 5V pin. The BATT input is disconnected.

These were running 1.3.6/8 firmware beforehand. The Diagnostic page of Metabase does not populate so I only have the raw values through the nRF Connect app:
Model String No.: 0x35
Hardware Rev String: 0x302E33
Firmware Rev String: 0x302E332E31

The operation fails when after pressing 'UPDATE FIRMWARE'. A loading circle briefly happens and the following message pops up
"Error Failed to connect to 'MetaBoot'. Would you like to try again? Operation Failed: Device disconnected unexpectedly"

I am using an iPhone 7 Plus with Metabase app 4.2.1, and have repeated this with a iPhone XS with the same results. I have also used a Google Pixel 3 and Samsung Galaxy S8, however these do not show up under the Metabase app.

As a result, two soldered IMU devices that I have attempted to update to 1.4.4 from 1.3.6/8 no longer work and are stuck in MetaBoot. These were working fine beforehand.

Does firmware 1.4.4 require the BATT connection to be utilized? If so, can the BATT and 5V input pins be bridged to fool the device into working?

What other solutions am I able to take?


  • edited February 2019

    Try updating the firmware as described in this post:

    Can you provide a circuit diagram showing how the MetaMotion is connected to your PCB?

  • Hello Leonard,

    None of the MMR series devices are specified to work without the battery connected. The only officially supported configuration includes the battery. This applies to all firmware versions.

    The issue is that the battery charge management IC is providing the down regulation from 5v, and unfortunately has a several millisecond timeout when switching the charge current on and off. This is too long for the device to operate the radio reliably off of the system capacitance and the voltage dips too low.

    The unofficial recommendation if you are mounting to a carrier pcb, is to add 100uF or more capacitance in place of the battery. If power requirements permit, adding a small static load (on the order of a mA) will help to keep the charger from switching off.

    Alternatively, if a 3V source is available, directly driving the 3V will shut off the internal regulator and supply power directly. All systems and subcircuits are powered by the 3V supply, so no functionality is lost.

    It may be okay to attach 5V directly to the BAT input, but we have not tested this configuration.

    None of these configurations are officially supported, doing so is at your own risk.


Sign In or Register to comment.