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Sensors, Electronics and Prototyping

UM7 Calibration Procedure for Firmware Revisions U71D, U72A

** If you are using firmware revisions (U71A, U71B, U71C) look here.

All Redshift Labs UM7’s and UM7-LT’s are pre-loaded with firmware revision U72A or newer.

Equipment and parts required

The following equipment is required for the calibration of your UM7 or UM7-LT

  1. 5-Pin 2-Way Cable (Comes standard with a USB Serial Converter)
  2. UM7 or UM7-LT
  3. Redshift Labs USB Serial Converter
  4. Serial Interface Software (Pre-installed with latest FTDI drivers)
  5. Anti-static wrist band
  6. USB A PLUG TO USB MINI B

Instructions

1. Preparation

Get all equipment and layout neatly, ensure anti-static wrist strap is worn at all times.

2. Connect USB Converter

Attach the 5-Pin 2-way cable into the UM7’s or UM7-LT’s, 5 pin JST header, plug the other end into USB Serial Converter’s 5-Pin JST connector.

3. Attach USB Cable

Plug USB MINI B end into serial converter PCB, plug USB A end into PC (we recommend using USB 2.0 ports if possible)

4. Start Interface Software.

Launch Redshift Labs serial interface software by double clicking the icon on your desktop.

5. Set COM Ports

You will need to configure which virtual COM port has been allocated to your USB serial converter PCB. Select “Serial Interface > Serial Settings > Port > COMX” (where X is the allocated COM port number on your PC, in our case it was COM3):

6.  Connect to your UM7 or UM7-LT

Select “Serial Interface > Serial Settings > Connect”.

7. Read Data

Read the data from within your UM7 or UM7-LT, select “Serial Interface > Configuration > Read”. A progress bar should load and once it’s finished the configuration data should be displayed.
Press the + button next to “Broadcast Rates – Raw Data” now select “All Raw Broadcast Rate”, verify that it’s set to 20 Hz. If not, type 20 into the corresponding text box and press “Serial Interface > Configuration > FLASH”.

8. Plot Data (Optional)

We usually start plotting some data about now, so we can watch the following calibration steps in real time.

  1. From the tabs select “Data”
  2. Click the + icon next to “Euler Angles”
  3. Tick Roll, Pitch and Yaw checkboxes
  4. Press “Serial Interface > Data > Create Graph from Selected”.
  5. A real time graph should be displayed in a separate window of Roll, Pitch and Yaw. We suggest using your mouse to expand the window a little.

9. Start Magnetometer Calibration

To begin magnetometer calibration select “Serial Interface > Mag Calibration > Start Data” you should notice that the “Collected Data Points:” begin counting up. While the software is taking samples, rotate your UM7 or UM7-LT around in a spherical position capturing as many different samples of the surrounding magnetic field as possible. Keep well away from anything that will produce magnetic distortions in your sample set, i.e. ferrous metal or powerful magnets.

10. Stop Collecting Data

When you see that the “Collected Data Points:” number turns green, that’s an indication that you have collected the minimum samples required to perform a calibration. I usually collect about 500samples. Now select “Serial Interface > Mag Calibration > Stop Data”.

11. Compute Biases

You are now ready to compute the biases for calibration, select “Serial Interface > Mag Calibration > Compute”. You should now see some computed data in the “Calibration Matrix”. Select “Serial Interface > Mag Calibration > Write to RAM”.

12. Write Calibration Data

You will want your calibration data to persist, so now select “Serial Interface > Configuration > FLASH”. This will write the calibration data into your UM7 or UM7-LT, the calibration matrix will be stored even if the power is turned off and back on.

13. Zero Rate Gyros

This is needed in the later sets of firmware. It will initialise your new calibration correctly.
Select “Serial Interface > Commands -> Zero Rate Gyros”.

14. Set Magnetic Reference Vector

Point your UM7 or UM7-LT exactly North on the UM7 (it’s the X direction on the top label), now press “Serial Interface > Commands > Set Mag Reference Vector”.

15. Reset EKF

You will now need to reset the EKF for the process to work correctly. You may notice that the graphs on your data plot are displaying incorrectly. Select “Serial Interface > Commands > Reset EKF”. Now look at the data plot of Roll, Pitch and Yaw. If you point the X orientation of the sensor North and hold the unit as level as possible, you should see the Roll, Pitch and Yaw converge to zero.
Video of the calibrations steps outlined above:

** Note

If you are running an earlier version of firmware (U71A, U71B, U71C), please refer to this video of Caleb Chamberlain from CH Robotics showing how to get started with the UM7, configure its communication settings, and calibrate its magnetometer.