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Mojo Quickstart

Mojo (short for “More Joules”) is a small, inexpensive Notecard companion device that measures energy usage in a battery-powered system. Inspired by the Joulescope and powered by a low-power coulomb counter, Mojo is designed to give product builders an inexpensive way of measuring the performance, charge, and state of deployed applications intended to operate on battery power over long periods of time.

The front of a Blues Mojo

In this quickstart tutorial you'll learn how to connect a Mojo to your hardware, configure a Mojo using a Notecard, and learn how to view Mojo data in Notehub.

Let's get started.

Before You Begin

To complete this quickstart, make sure you have access to the following:

Connect a Mojo

To use Mojo to measure energy consumption you must:

  • Connect a battery to Mojo's BAT JST connector.

  • Connect the device you want to measure energy consumption for to Mojo's LOAD JST connector. For this tutorial you can connect your Mojo's LOAD JST connector to your Notecarrier's LIPO or VBAT JST connector.

  • Connect Mojo to a Notecard over I2C, which is most easily done through one of Mojo's Qwiic connectors.

warning

Notecard will only detect the presence of a Mojo if they are connected prior to Notecard being powered on.

The image below shows one way to wire this up using a LiPo battery, a Notecarrier X, and a Notecard Cell+WiFi.

A Mojo connected to a LiPo battery and Notecarrier X

note

You can use either of Mojo's two Qwiic connectors to make an I2C connection with a Notecard. The Mojo offers two Qwiic connectors in case you want to daisy chain additional I2C peripherals.

Configuring Mojo with Notecard

Notecard detects the presence of a Mojo on the I2C bus automatically, without the need for any configuration. To get data from Mojo though you need to take one of two approaches.

Using the card.power Request

The Notecard offers a card.power request you can use to take a power consumption reading from Mojo at any time.

To try it, connect a USB cable from the Notecarrier's USB port to your computer's USB port, and then connect your Notecard to the In-Browser Terminal.

Once connected run the command below from the Terminal.

{"req":"card.power"}

You should see a response like the one below.

{
 "temperature": 19.154992675781273,
 "voltage": 4.201925659179688,
 "milliamp_hours": -74.61733499999998
}
note

To use Mojo your Notecard must be running a firmware version >= 8.1.3. You can check which firmware version you're using with the card.version request.

If you're running an older version you must upgrade your Notecard's firmware to continue. You can upgrade your Notecard's firmware from the In-Browser Terminal using the firmware install latest command.

Here, temperature is a reading from your Notecard's onboard temperature sensor, voltage is your current device voltage, and milliamp_hours is the number of milliamp hours (mAh) consumed by your device, as measured by Mojo.

It's likely that your initial milliamp_hours reading will be negative, as Mojo measures cumulative energy readings (aka both charge and discharge from the connected battery). All Blues Notecarriers have the necessary wiring to charge connected LiPo batteries when they have a powered USB connection, so your battery has likely charged more than discharged at this point in the tutorial.

The milliamp_hours field that Notecard tracks is cumulative. You can reset the counter at any time using the card.power request's reset argument.

{"req":"card.power","reset":true}

Enable Power Logs

Another approach you can take for taking readings from Mojo is to enable automated logging. With this approach, your Notecard will automatically take a reading from Mojo every time it powers its modem on and off, and will store that data in a _log.qo Notefile.

To enable power logs, you first need to set the _log environment variable on your Notecard. To do so complete the following steps:

  1. Ensure your Notecard is connected to a Notehub project. If you're new to Notecard and not sure how to do this, refer to the Notecard Quickstart tutorial.

  2. Open your Notehub project, double click on your device, and visit its Environment tab. The Environment tab in Notehub

  3. Create a new environment variable with a Key of _log and a Value of power. The Environment tab in Notehub with values provided

  4. Click the Apply changes button to save your new variable.

  5. Return to your Notecard in the In-Browser Terminal, and run a hub.sync request to pull down the new environment variable to your device.

    {"req":"hub.sync"}

  6. With the _log environment variable set, your Notecard will now automatically collect energy-usage data in _log.qo Notes every time its modem is powered on and off. To try it out, perform an additional hub.sync request on your device:

    {"req":"hub.sync"}

  7. After this sync completes, return to your Notehub project and visit the Events tab. You should see a new _log.qo event. An _loq.qo event in Notehub

Each _log.qo event contains the cumulative mAh count in the milliamp_hours field, as well as information on the energy consumed since the last modem power on/off in the text field.

If you'd like to take additional energy readings that are not tied to the device's modem, you can enable them with the card.power request's minutes argument. For example, the request below enables hourly _log.qo entries.

{"req":"card.power","minutes":60}

Testing Mojo

With power logs enabled, let's do one last test so you can see Mojo in action. In this section you'll use the card.temp request to take regular temperature readings, and monitor the energy used in the process.

  1. Run the command below on your Notecard using the In-Browser Terminal. This request tells your Notecard to take a temperature reading from its onboard sensor every minute, and to immediately synchronize that data to Notehub.

    {"req":"card.temp","minutes":1,"sync":true}

  2. Next, unplug your Notecarrier from your computer so your device is running on battery power.

  3. After that, wait a few minutes to give your Notecard some time to take and send a few readings.

  4. Finally, reopen your Notehub project and visit its Events page. You should see a list of _log.qo events with an increasing amount of milliamp_hours used. (Tip: You may wish to filter for _log.qo events as I'm doing in the screenshot below, as it allows you to see only your energy-consumption data.) List of _log.qo events in Notehub

  5. Once you've gathered enough data to see how Mojo works, you may wish to reconnect your Notecard to the In-Browser Terminal and run the following command, which turns off automated temperature reporting.

    {"req":"card.temp","stop":true}

Next Steps

Now that you know the basics of how Mojo works, you're ready to start using it to measure energy consumption in your own projects. Here are some resources you may find useful as you start experimenting with Mojo.