ZOE-M8Q/SAM-M8Q - Low power mode?

GPS/GNSS Development Boards
1

Hi there,

I recently purchased the [SparkFun GPS Breakout - ZOE-M8Q (Qwiic) and [SparkFun GPS Breakout - Chip Antenna, SAM-M8Q (Qwiic). I’ve been tinkering with both receivers to try and achieve the lowest quiescent draw possible, but have hit a bit of a wall.

Gaining control over the receiver can be achieved by configuring UBX-CFG-PM2 to use EXTINT pin control in u-center. Below is a snippet from the [M8 Receiver Description.

13.2.2.10 EXTINT pin control

If both Force-ON and Force-OFF features are enabled at the same time, the receiver PSM operation will be completely in user control. Setting ‘high’ on the configured EXTINT pin will wake up the receiver to get a position fix and setting ‘low’ will put the receiver into sleep/backup mode.

The good news is I’ve been able to successfully control the ON/OFF operation of the receiver by enabling the EXTINT functionality and connecting a jumper from the INT pin of the receivers to a digital pin on the SparkFun Qwiic Micro - SAMD21 board I’m using.

The bad news is that despite both the ZOE-M8Q and SAM-M8Q datasheets listing a sleep/backup current draw of 15-20 uA, I am measuring 160 uA on both SparkFun M8Q receiver boards when turned OFF. This value is measured using a Fluke 287 between a couple Qwiic breakout cables.

I’m at a bit of a loss as to where the extra ~140 uA draw could be coming from and am curious if anyone has been able to achieve a lower power consumption than this with the receiver put to sleep. 140 uA is a pretty significant quiescent draw I hope to be able to eliminate in order to enable long-term, battery-based deployments.

Cheers,

Adam](https://www.u-blox.com/sites/default/files/products/documents/u-blox8-M8_ReceiverDescrProtSpec_(UBX-13003221)_Public.pdf)](SparkFun GPS Breakout - Chip Antenna, SAM-M8Q (Qwiic) - GPS-15210 - SparkFun Electronics)](SparkFun GPS Breakout - ZOE-M8Q (Qwiic) - GPS-15193 - SparkFun Electronics)

2

Hi Adam.

The current figures in the data sheets for both GPS’s are for the GPS chip itself rather than the assembly.

Both GPS breakouts have a battery on board that will be getting charged when power is applied. The extra current you’re seeing might be from that, or it could be parasitic draw from other parts on the board.

3

Thanks Chris,

It appears that the ML414H lithium battery is indeed the culprit. I left the receivers connected overnight to charge the batteries and the sleep/backup current dropped from ~160uA to ~30 uA. The current draw does tend to fluctuate, so the battery must be constantly discharging/charging. It’s too bad there isn’t a jumper allowing users to easily to disconnect the battery, but at least the quiescent draw is much lower now.

Cheers,

Adam