Little Bee

An affordable, high-performance current & magnetic field probe

Jul 02, 2021

Project update 9 of 9

Shipping Soon!

by Weston Braun

I am excited to announce that all 200 Little Bee units are on the way to Crowd Supply’s warehouse for final distribution! This means that orders will start shipping soon. Please take this time to check your delivery address, and update it through your Crowd Supply account if needed. Updating your shipping address helps avoid delays and get your orders shipped successfully. Once your order details have been sent to the warehouse team for processing, it can be hard or impossible to re-route a shipment. Please contact Crowd Supply Support with any shipping questions or concerns.

The last few weeks have spent making some last minute tweaks to firmware, reworking a number of board that had their sensors damaged at the PCBA house, and assembling and testing all 200 units. What do you call a big pile of Little Bee units? A bee hive?

Firmware Updates

The auto-zeroing functionality has been improved to reduce the time it takes the probe to auto-zero and to increase the auto-zeroing accuracy. The Little Bee now typically auto-zeros to a mV of true zero, which is close to the noise floor of many oscilloscopes. Additionally, I added an absolute field sensing mode that is triggered when both buttons are held down when the probe is turned on. In this mode the polarity of the sensor is flipped at 55Hz, generating an AC signal with a peak to peak amplitude of twice the magnetic field strength. This can be used to check for high ambient fields that could impact the normal operation of the probe or for sensing very small magnetic fields with some additional digital signal processing.

If you are ever lost without anything else besides a Little Bee and an oscilloscope it would also make it a bit easier to use the unit as a compass.

Production Testing

During production the gain of every Little Bee unit was calibrated and the frequency response was measured. Each Little Bee unit is serialized and you can find the test data on the project GitHub repo. Below is a plot of the production test data for all of the Little Bee units. The outliers in the data are from early production when the oscilloscope used for measurement had a 20MHz bandwidth limit on and when the frequency response was measured prior to gain adjustment. As seen in the plot, the -3dB bandwidth of 10MHz was vastly exceeded!

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