If you have been developing an IoT device that requires positioning, such as smart watches or trackers, you might have come across the Zoe M8 series GNSS SIP (System-In-Package) from u-blox. The M8G, which is very small, and so suits the above mentioned applications, has been on the market for some time. According to the data sheet it has a typical current consumption of 40 mA in full-power continuous tracking mode and 12.5 mA in the 1 Hertz power save mode. This current consumption is measured at 1.8V and with GPS and GLONASS enabled.
There’s now a new member of the family called Zoe-M8B. It is pin-to-pin compatible with the M8G but what is interesting is that it has a new power mode called Super-E which is short for Super-Efficient. According to the data sheet the mode gives a typical 1 Hertz Super-E tracking current consumption of 8.3 mA in the same configuration with GPS and GLONASS enabled. Since we’re curious about the new Super-E technology, we decided to check it out in two scenarios.
In the measurement setup, we used the Zoe-M8B evaluation board connected to Otii Arc, to power the board and measure the system level power performance. To monitor the GNSS/GLONASS receiver status, we used the u-blox u-center software.
The first scenario was a typical office environment, actually our developer corner. For this indoor scenario we used an active antenna, positioned close to the window to make sure that we received a good signal. Please note that the antenna power consumption was not taken into account in the measurements.
Once the measurement started, the board went into Super-E mode (as indicated by Power Optimized Tracking in the u-center software) and an average current consumption of 15 mA was measured. We were not able to get down all the way to the 8.3 mA as stated in the data sheet, even though Super-E kicked in. The building for the indoor scenario is fairly RF tight (floor 5 in a 6 floor building, with coated windows facing North), which does cause problems with the reception quality.
After indoor measurements, we decided to use a more realistic environment and moved our setup outdoors. Once outside, the Zoe-M8B evaluation board, (now with a passive antenna) but in the same setup as for the previous case, entered Super-E Power Optimized Tracking mode and we could verify the average power consumption to be close to the data sheet indicative values, at approximately 8.5 mA.
During the power measurements in these two particular scenarios, we discovered that the receiver entered Super-E mode but with different duty cycles, which has a direct impact on power consumption. In the indoor scenario a lower signal to noise ratio with fewer tracked satellites was acquired resulting in longer duty cycle compared to the outdoors one. The measurements showcase the low power performance of u-blox M8B as well as the importance of testing your IoT device in different scenarios. It is crucial to take into consideration that different components of your device will be behaving differently depending on the surrounding environment. This is why it is always a good idea to regularly check the performance in realistic environments during development in addition to testing every time when updating your software and firmware.
Download the full Otii project linked below in Downloads to check out the above discussed measurements.
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The Qoitech Team