This page details the step by step instructions for taking accurate deep sleep current measurements of the EM250/EM260 chips by using an InSight adapter, the appropriate RCM, a 3.3V power supply, and a current meter. 

This tutorial will detail how to make deep sleep current measurements of the EM250/EM260 chips using the development kit hardware. 

Introduction

The Ember development kit is designed for rapid prototyping of application software for use with the EM250/EM260. Unfortunately, the original versions of this development kit hardware were not designed for taking accurate sleep current measurements. Peripherals required for effective software design will drain significantly more current than the EM250/EM260 even in the deepest sleep. Further, there exists no way to isolate the current consumption of the EM250/EM260 on their respective development kits. Finally, the RCM designs require a small re-work to achieve the best possible deep sleep current performance. In deep sleep, one of the debug lines requires a pull-down resistor (absent in some older versions of the RCM board design) to prevent it from floating to an intermediate value and needlessly consuming micro amps of current. (If you are unsure whether the resistor is present, you can check the schematic for your RCM, found at the end of the RCM Technical Specifications for your board, located in the EmberZNet release that came with your kit. Ensure that the revision of the board in the schematic matches the revision noted on the silkscreen for your hardware.)

This document details how to use the EM250/EM260 modules supplied with their respective development kits to obtain accurate deep sleep current measurements.

Step 1: Hardware Modification

 As alluded to in the introduction, the EM250/EM260 require the addition of a pull down resistor on one of the pins of the 10 pin debug header . You need to solder a 10k resistor between pin 4 (SIF_MOSI) and pin 5 (GND) of the 10 pin debug header.

 Step 2: Software Upload

 As part of this HOW TO, there are two ZIP files with special versions of rangetest. They differ from the version of the rangetest application shipping with 2.5.3 and earlier versions of our node software in that the command to enter deep sleep, or "SHUTDOWN" command now takes a parameter. This parameter specifies the number of seconds before the deep sleep mode activates. This is important because InSight Adapters, when connected to the EM250/EM260, constantly poll the device through the debug port. This polling will wake the device from deep sleep. In order to successfully put the EM250/EM260 into sustained deep sleep, the command must be issued, the InSight Adapter must be disconnected from the module, and then the command must execute.

 To upload the software, download the appropriate rangetest image for your specific module, either EM250 or EM260 and unzip the .xdv and .xpv images to a known directory. Connect the module to your InSight Adapter, making sure that the RCM Power Select on the front of your InSight Adapter is switched to the rightmost or "Int" power mode. This will force the InSight Adapter to supply the power to your RCM. Power cycle the InSight Adapter (this is not necessary if you only have an EM250 or EM260 development kit). Connect to the InSight Adapter using InSight Desktop. Use InSight Desktop to upload the rangetest image to your module.

 
Step 3: Test Setup

After uploading the appropriate range test image, it is time to isolate the RCM and power it from an external power supply. Unplug the RCM from the breakout board, and supply a 3.3V power source directly to the VCC and GND pins on the underside of the module. You will need to refer to the module pinout in the module technical specification to select the correct pins. Make sure to put your current meter in series with the RCM. Make sure to switch the RCM Power Select from "Int" to "Ext" so that the InSight Adapter does not attempt to power the RCM in parallel to the external power supply.

Step 4: Putting the Node into Deep Sleep

Now that the module is running rangetest, and the hardware is set up to make a current measurement, it is time to put the module into deep sleep. Accomplish this by connecting to the rangetest application via the virtual serial port. To do this, you will need to telnet into the InSight Adapter's port 4900. If you are unsure of your InSight Adapter's IP address, you can easily look it up in InSight Desktop in the Adapters pane. Expand the information of your InSight Adapter by clicking on the " " side to the left of the InSight Adapter's name, and look for the "Address:" line. 

 Once you are connected to the virtual uart, issue the command "shutdown 8". This gives you 8 seconds to disconnect the InSight Adapter before the RCM enters deep sleep mode. After the RCM enters deep sleep mode, you may take your deep sleep measurements.

 
Step 5: Exiting Deep Sleep

There are two ways to exit deep sleep. Plugging in the InSight Adapter should eventually wake up the RCM by simulating an interrupt to the EM250/EM260. Additionally, power cycling the RCM will cause it to wake up from deep sleep.