In the latest versions of battery powered device firmware (released Q4 2019) we have implemented an Under Voltage Lockout (UVLO). This will power down the device when the batteries are supplying too low a voltage to operate reliably.
Without this feature there are circumstances where the device may have enough power to boot up, but as soon as the modem/GPS is turned on and draws more power - the device will brown out.
The UVLO avoids cases where the device will be stuck in a Boot/Reboot loop. Additionally it helps protect the modem and other sensitive electronic components from damage.
Without the UVLO, on low voltages, the LED may also be able to flash. The UVLO ensures that a device that won't be able to connect reliably due to low voltage will also show no 'signs of life' - prompting the user to use a fresh set of batteries which will allow the device to operate correctly.
UVLO Thresholds and Behaviour
- If <2.8V (3.2V/cell LTC ) is detected on start up, the device will not start due to the UVLO
- In practice this is closer to 3V (3.3V/cell LTC), as a load such as switching on the modem causes the battery voltage to drop, and this could trigger the UVLO threshold if operating in this range.
V1: If the voltage dips below 2.8V total for LiFeS2 or 3.3V/Cell LTC while running, the device will sleep for 3hrs to attempt to allow it to recover.
V2: As of October 2020 a couple of changes to the UVLO firmware were made
- This feature was adjusted to also keep track of how many times the device goes to sleep. This count is stored in flash. If the device has a reset due to under voltage 10 times, it will then sleep for 1 week after this 10th reset. A hard reset (i.e. battery change) will reset this count. Make sure to remove the batteries when changing for 20-30 seconds to allow the device to completely reset.
- Additionally, if a UVLO reset occurs, the 'battery good' flag in the digital input data will be set to '0' (i.e. battery is bad). This will mean if the device wakes up again after 3hrs and manages to upload, a low battery alert will be sent. For more information on this flag and low battery alerts see Battery Life, Battery Capacity Estimate & Low Battery Flag.
- These updates apply to the following firmware versions
- Falcon - 2.11/3.11
- Remora2 - 2.16/3.16
- Oyster2 - 2.14/3.14
- Eagle - 2.9/3.9
- Yabby GPS - 2.17/3.17
- Yabby Wi-Fi - 2.8/3.8
Min operating voltage
- The cellular modem requires at minimum around 3.1V or 3.3V LTC to operate reliably.
Yabby GPS/Yabby Wi-Fi/Oyster v1
- Device won't start with <3V according to UVLO
- As per the above for the Remora2/Oyster2/Falcon/Eagle.
- Yabbies Won't run with <2.8V according to UVLO
- The Oyster v1 UVLO threshold is 2.5V, turning on the modem causes the battery voltage to drop quite significantly, so the threshold is set a bit lower in firmware. So effectively the threshold is around 2.8V like the Yabby for what the batteries must supply.
The fact that the device will sleep for 3hrs when the batteries are running low will make it appear that the device is having trouble connecting. Usually the first thing that is noticed is the fact heartbeats/uploads are missed - but then recovering.
Without the UVLO - this device might have simply dropped out. Check the battery level/percentage. If it is low it is likely the reason the device is not operating reliably.
A UVLO reset is indicated by the reset code 0x14 in the device logs in OEM.
For information about other reset codes, see Common Reset Reasons