RoadTest: EFM32™ Zero Gecko Starter Kit w/ Sensor Card
Author: nermash
Creation date:
Evaluation Type: Evaluation Boards
Did you receive all parts the manufacturer stated would be included in the package?: True
What other parts do you consider comparable to this product?: null
What were the biggest problems encountered?: There is nagging issue when pluging the board in the USB 2.0 port, windows keep reporting "this device can perform faster". I tried J-Link update 4.95b, but the issue remains.
Detailed Review:
First of all, I would like to thank Silicon Labs and Element14 for providing me with a review unit of EFM32 Zero Gecko development board with BRD8001A EXP EVB weather station expansion board.
I have been interested in Silicon Labs (former Energy Micro) products for some time now, ever since I saw a review of Giant Gecko board by Eevblog on Youtube.
What is in the box?
In the box you get the EFM32 Zero Gecko board and the sensor board, with the ubiquitous mini USB cable. One noticeable thing missing is the lithium button cell CR2032, probably due to silly regulation preventing air transport of any type of lithium batteries, whether it is a lonely small CR2032 or a complete battery pack for Tesla car...
This is the Zero Gecko board itself. Very nicely laid out, black solder mask with white silk screen and gold plated solder pads.
Top left side of the board is occupied with the USB interface, J-Link debugger and Advanced Energy Management circuitry. On the bottom left is the CR2023 battery holder and switch for selection of powering via battery or the debugger. Centre of the board is reserved for a nice Sharp 128x128 pixel memory TFT LCD, with two push buttons PB1 and PB0 below it. My guess is that board controller IC is siting underneath the lcd. User interface is expanded with two leds LED1 and LED0 and two capacitive touch buttons. There is also a reset push button which is always welcomed feature on development boards. On the far right there is expansion header, labelled EXP, with standard 2.54 mm header spacing.
Just below the EFM32 Zero Gecko silkscreen sign there is a ARM M0+ core EFM32ZG222F32 MCU with 32 KB Flash and 4 KB RAM, with its high frequency 24 MHz oscillator and low frequency 32.768 kHz crystal.
On the top and bottom of the board there are labelled breakout pad of all the microcontroller pins for easy access to external devices.
This is the expansion sensor board that comes with the kit.
Board features pass through expansion connectors, Si1147 UV and proximity sensor (U4 top centre), Si7013 humidity and temperature sensor (U2 centre right), and three IR leds for 2D gesture recognition (marked DS1, DS2 and DS3) placed in triangular pattern for optimum coverage. There is also a ribbon connector (J6) for routing of I2C bus to external devices.
Here is the picture of the complete setup running the weather station demo program.
Simplicity studio
Silicon Labs is offering for free IDE called Simplicity Studio. It is based on Eclipse IDE, and it supports their 8051 and EFM32 mcus,and it is about a 1 GB download just for the EFM32 family.
One nice thing for easy start is the first screen when you start it. It is sort of a central point for all development and tinkering endeavours, since you can access the IDE itself as well as other tools, software and documentation. I like this easy, polished and clear gateway.
Main tools are:
Simplicity IDE
Another great asset is Kit Documentation, easy access for all kit documents: manuals, schematics, assembly drawings, bill of materials.
Advanced Energy Management
This is the feature that I have been interested in the most. It employs impressive engineering scheme to give you the highly accurate and precise current consumption measuring (when working on +5V USB power, of course)
How does it work?
Well, they really went to town on this one, and here is the part of schematics displaying this feature.
Voltage supply first goes through a linear low-dropout regulator dropping the voltage from 5V to 3.3V. Current goes through 4.7 Ohm shunt resistor R701 with two lines sensing the voltage drop going to the current measurement section.
Here the two sense lines are connected as differential inputs to the precision zero drift current sense amplifier U703.
The signal then goes through second stage of amplification, depending on the current range being selected, through either one of two low noise precision CMOS op amps.
Current ranges are 0.1-250 uA with 1 uA accuracy and 100 nA resolution, and 250 uA - 50 mA with 0.1 mA accuracy. ADC sample rate for current measurements is 6250 samples/s.
This all exercise in precision amplifiers is done to avoid having a large value shunt resistor for current measurement, which would allow for a much simpler measuring setup, i.e. feeding directly to ADC,
but large value of shunt resistor would also increase burden voltage, reducing the available voltage headroom for normal operation.
For more details on burden voltage please refer to Eevblog videos on Youtube, and his uCurrent project (basically the same thing as this AEM).
And another nice bit of engineering, on every startup this AEM system is first calibrated via 4 resistors for precise current measurement, in the ranges of 3.3 uA up to 3.3 mA. This is done to eliminate any offset errors in the amplifiers, giving the best possible accuracy for the session.
Is it accurate?
Here is the screenshot of the Energy profiler window while running temperature measurement of the weather station demo program.
Average current measured is 3.60 mA RMS, I have tested this with my Fluke 287 meter on AC mV range (100 kHz BW) acros the 4.7 ohm shunt resistor.
Results were between 17.0 and 17.6 mV, which would translate to 3.61-3.74 mA current. I would say that the AEM measurement is pretty much spot on!
To be continued...
